Myopia

Myopia is a refractive condition in which light entering the eye focuses in front of the retina when accommodation—the adjustment of the eye’s focusing power—is relaxed. Distant objects consequently appear blurred, while objects within a nearer range may remain clear. Most myopia results from an eye that is too long relative to its optical power, although changes in the cornea or crystalline lens can also produce a myopic refractive state. Its definition rests on optical principles, while its development involves both genetic susceptibility and environmental influences. (nei.nih.gov)

Myopia commonly develops during childhood and can progress through adolescence and into adulthood. Spectacles, contact lenses, and refractive surgery can correct its optical effects; interventions intended to slow progression address a different clinical objective. Higher degrees of myopia are associated with increased risks of retinal detachment, glaucoma, and other ocular complications. High myopia, defined by refractive magnitude, is distinct from pathologic myopia, which involves structural damage to the eye and may reduce vision even with optical correction. (nei.nih.gov)

The condition is an important public health concern because of its frequency, its contribution to uncorrected vision impairment, and the long-term consequences of myopia-associated disease. Understanding it requires consideration of eye growth, population patterns, inherited and environmental risk factors, diagnostic measurements, correction and progression-control methods, and the accessibility of eye-care services. (myopiainstitute.org)

Optical basis and refractive measurement

The cornea and crystalline lens form the eye’s principal image-focusing system. Their combined optical power must match the distance to the retina, determined largely by axial length—the eye’s front-to-back dimension. In an emmetropic eye, parallel rays from a distant object converge on the retina when accommodation is relaxed. In a myopic eye, they converge in front of it, so the retinal plane receives a defocused image rather than a sharply focused point. This mismatch can arise because the eye is too long for its optical power, because the cornea or lens has excessive power, or through both mechanisms. The International Myopia Institute’s 2019 report, led by Daniel Ian Flitcroft, therefore defines the optical state in terms of focus with accommodation relaxed, rather than eye length alone. (myopiainstitute.org)

The far point is the object position conjugate to the retina when accommodation is relaxed: effectively infinity in emmetropia, but a finite distance in front of an uncorrected myopic eye. In a simplified spherical model, neglecting spectacle vertex distance, its distance in metres is approximately $r=1/|R|$, where $R$ is the negative refractive error in diopters. Thus, calculated far points for $-1.00$, $-2.00$, and $-5.00$ D are approximately 1 m, 50 cm, and 20 cm, respectively. Objects beyond this point are blurred because their rays converge too far in front of the retina. Closer objects can be focused by accommodation, which increases lenticular power; the nearest clear position depends on the remaining accommodative amplitude. “Nearsightedness” therefore does not imply clear vision at every near distance, and stronger myopia shifts the uncorrected focusing range closer to the eye. (govinfo.gov)

A diopter (D) expresses optical power as the reciprocal of focal length in metres: $P=1/f$. In corrective-lens notation, positive power denotes convergence and negative power divergence. A negative myopic prescription does not mean that the eye itself has negative optical power; it specifies the diverging lens needed to compensate for excessive convergence relative to retinal position. Such a lens makes incoming distant rays diverge before entering the eye, allowing their retinal focus to shift backward onto the retina. The prescription measures an optical correction, not axial length or the condition of retinal tissue. (ncbi.nlm.nih.gov)

A spherocylindrical prescription records sphere $S$, cylinder $C$, and cylinder axis. Its spherical equivalent is $SE=S+C/2$, retaining the cylinder’s sign. For example, a sphere of $-2.00$ D with a cylinder of $-1.00$ D gives $SE=-2.50$ D. In regular astigmatism, the two perpendicular principal meridians have different refractive powers; their average gives the spherical equivalent. This is useful for summarizing refraction in population studies, but it discards cylinder magnitude and orientation. Consequently, two eyes with the same spherical equivalent can have different optical blur, and a spherical-equivalent lens does not reproduce a full astigmatic correction. (pmc.ncbi.nlm.nih.gov)

These optical states are distinct but not mutually exclusive. Emmetropia describes distance focus on the retina without accommodation; hyperopia describes a relaxed-eye focus behind the retina, which available accommodation may move forward. Astigmatism produces different focusing powers in different meridians and can accompany either myopia or hyperopia; in mixed astigmatism, one principal meridian is myopic and the other hyperopic. Presbyopia is the age-related loss of accommodative focusing ability, rather than the opposite of myopia. A person can therefore remain myopic while developing presbyopia: removing distance correction may permit clear viewing near the uncorrected far point, but does not restore the lost accommodation. (ncbi.nlm.nih.gov)

Definitions and clinical classification

The International Myopia Institute (IMI), in its 2019 report led by Daniel Ian Flitcroft, defined myopia quantitatively as an eye’s spherical equivalent refractive error of $\leq -0.50\ \mathrm{D}$, measured with accommodation relaxed. High myopia is $\leq -6.00\ \mathrm{D}$; low myopia spans $-6.00\ \mathrm{D} < \mathrm{SE} \leq -0.50\ \mathrm{D}$. Thus, exactly −6.00 D belongs to the high category. These are eye-specific, spectacle-plane measurements, not classifications automatically assigned to both eyes of a person. Relaxed accommodation is essential because active focusing can make measured refraction more negative, especially in children; detailed measurement procedures are distinct from the definitions themselves. (pmc.ncbi.nlm.nih.gov)

Axial myopia describes an eye whose front-to-back length is excessive relative to its corneal and lenticular optical power. Refractive myopia instead attributes the myopic state principally to the cornea or lens: their curvature, optical properties, structure, or position produces excessive focusing power relative to eye length. Both mechanisms can coexist. Secondary myopia is an etiological category: a specific cause, such as a medication, corneal disease, or systemic clinical syndrome, can be identified. Ordinary population risk factors do not qualify as such causes. Consequently, “secondary” and “axial” or “refractive” describe different dimensions of classification rather than mutually exclusive alternatives. (myopiainstitute.org)

High myopia and pathologic myopia are not interchangeable. The former records refractive magnitude; the latter identifies structural pathology associated with myopic axial elongation in the posterior eye, potentially reducing best-corrected visual acuity. Examples include posterior staphyloma—a localized outward deformation of the eye wall—and myopic maculopathy. An eye meeting the −6.00 D threshold need not have these lesions. Conversely, pathologic changes can occur without meeting that refractive threshold: posterior staphyloma has been documented in eyes shorter than 26.5 mm, including eyes of normal axial length. The IMI definition therefore imposes neither a minimum negative prescription nor a fixed axial-length cutoff for pathologic myopia. (pmc.ncbi.nlm.nih.gov)

Pre-myopia is a childhood risk category, not established myopia. Its refractive interval is $-0.50\ \mathrm{D} < \mathrm{SE} \leq +0.75\ \mathrm{D}$, but membership also requires an age-dependent combination of baseline refraction and other quantifiable risk factors indicating sufficient likelihood of future myopia to warrant consideration of preventive interventions. The interval alone is insufficient. Relevant factors include parental myopia and the trajectories of refraction and axial growth. The report’s longitudinal evidence illustrates the age dependence: predictive refractive thresholds ranged from below +0.75 D at age six to 0 D or less at age eleven. (pmc.ncbi.nlm.nih.gov)

Fixed thresholds standardize research without marking biological discontinuities. Measurement variation can move an eye across −0.50 D, while ocular-disease risk does not begin abruptly at −6.00 D. Studies using alternative thresholds therefore require explicit definitions and comparisons with standard categories. Older labels also mix incompatible dimensions: “school myopia” combines onset context and presumed cause, whereas “degenerative,” “malignant,” and “progressive” have variously described severity, structural damage, or change over time. “Physiologic myopia” misleadingly suggests absence of adverse consequences, and “moderate myopia” has no consistently applied interval. Separate descriptions of refractive magnitude, anatomical mechanism, onset, progression, and structural complications avoid these ambiguities. (pmc.ncbi.nlm.nih.gov)

Population distribution and epidemiological trends

Myopia prevalence varies markedly with age, location, and survey period. Alicja Rudnicka and colleagues’ 2016 synthesis of 143 articles, covering 374,349 children in 42 countries, estimated prevalence at age 15 at 69% among East Asian populations, compared with 5.5% among Black African populations; these were modeled age-specific estimates, not measurements from single representative regional surveys. In Europe, a 2015 European Eye Epidemiology Consortium analysis of 61,946 adults estimated prevalence at 47.2% among 25–29-year-olds and 27.5% among 55–59-year-olds. Its definition—spherical equivalent of $\leq -0.75$ diopters—was stricter than the $\leq -0.50$-diopter threshold frequently used in childhood surveys, limiting direct comparison. (pubmed.ncbi.nlm.nih.gov)

Ancestry alone does not explain geographical differences. Kathryn Rose and colleagues’ 2008 comparison of children of Chinese ethnicity aged six or seven found myopia in 29.1% of the Singapore sample but 3.3% of the Sydney sample. Both studies used cycloplegic autorefraction and the same $\leq -0.50$-diopter threshold; parental myopia was also similarly common, at 71% and 68%, respectively. The samples nevertheless differed in mean age and reported activities, including outdoor exposure. This comparison demonstrates substantial variation within an ancestry category, but its observational design does not isolate a single environmental cause. Singapore’s findings should likewise not be treated as representative of every Southeast Asian population. (pubmed.ncbi.nlm.nih.gov)

Repeated surveys document secular increases independently of the differences between age groups within one survey. Five nationwide Taiwanese school surveys conducted between 1983 and 2000 found prevalence rising from 5.8% to 21% at age seven, from 36.7% to 61% at age 12, and from 74% to 84% at ages 16–18. These comparisons show that successive groups reached the same ages with substantially different refractive distributions. European data also indicate birth-cohort differences: Katie Williams and colleagues’ 2015 analysis reported age-standardized prevalence of 17.8% among people born in 1910–1939 and 23.5% among those born in 1940–1979. Cross-sectional age gradients therefore combine life-course refractive changes with differences between generations rather than directly measuring individual progression. (pubmed.ncbi.nlm.nih.gov)

Urban–rural differences are another recurring feature. Rudnicka and colleagues estimated adjusted odds of childhood myopia to be 2.61 times higher in urban than rural settings, with a 95% credible interval of 1.79–3.86. This is an odds ratio, not a 2.61-fold prevalence ratio. Urbanization encompasses correlated differences in schooling, household circumstances, and visual environments; the association does not establish an independent effect of population density. Its magnitude also varied between study populations, making “urban” and “rural” imperfectly comparable exposure categories across countries. (pmc.ncbi.nlm.nih.gov)

Survey methods can alter apparent geographical and temporal patterns. Age composition requires particular attention because a sample dominated by adolescents cannot be compared directly with one dominated by younger children; age-standardization applies a common population distribution. Sampling frames, participation, and exclusion criteria also matter: the European consortium consisted largely of Northern and Western European cohorts and excluded participants with certain conditions or previous procedures affecting refraction. In children, cycloplegia temporarily suppresses accommodation, reducing the tendency for active focusing to produce overly negative measurements. Rudnicka’s analysis found approximately twice the adjusted odds of measured myopia in studies without cycloplegia. Different diagnostic thresholds, instruments, and rules for combining the two eyes introduce further measurement uncertainty. (link.springer.com)

Global totals are consequently estimates assembled from heterogeneous evidence, not a worldwide census of measured eyes. Brien Holden and colleagues’ 2016 modeling study estimated 1.406 billion people with myopia in 2000, or 22.9% of the global population, and projected 4.758 billion, or 49.8%, for 2050. The reported uncertainty interval for the 2050 proportion was 43.4–55.7%. The same model projected high myopia in 938 million people, or 9.8%, in 2050. Its estimate of 34.0% for 2020 was a projection made before that year, not an observed global prevalence measurement subsequently established in 2020. These figures depend on the underlying survey evidence, extrapolated time trends, and population assumptions. (aaojournal.org)

Onset, progression, and the life course

Myopia commonly becomes apparent during the school years and progresses through childhood and adolescence, but its onset is preceded by measurable changes in eye growth. A 2007 analysis from the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) study compared 605 children who became myopic with 374 children who remained emmetropic. Those who subsequently developed myopia had less hyperopic refractive error four years before onset and longer eyes three years before onset. The fastest changes in refraction and axial length occurred during the year immediately preceding detection; both continued changing afterward, although more slowly. Thus, crossing a diagnostic threshold marks a point within a developmental trajectory rather than the beginning of all associated ocular growth. (pmc.ncbi.nlm.nih.gov)

Earlier onset is associated with greater eventual myopia, reflecting both a longer period available for progression and, in some cohorts, faster subsequent refractive change and axial elongation. A 2020 report followed 443 first-born twins who developed myopia in Guangzhou, China, using data collected from 2006 through 2018. At the final examination, at age 17 or older, high myopia—spherical equivalent of −6.00 diopters (D) or more negative—was present in 53.9% of participants whose onset occurred at ages seven or eight, 32.4% with onset at nine, 19.4% with onset at ten, and 1.3% with onset at twelve or later. These are cohort-specific outcomes rather than universal individual probabilities; the earliest-onset group contained only 26 participants. Earlier onset was also associated with longer axial length at follow-up. (pmc.ncbi.nlm.nih.gov)

Progression generally slows rather than stopping abruptly at a particular birthday. In the United States Correction of Myopia Evaluation Trial (COMET), a 2013 analysis fitted longitudinal refractive curves for 426 participants. Stabilization was defined as reaching within 0.50 D of the curve’s estimated final refractive value, not as the complete absence of subsequent change. By this definition, an estimated 48% had stabilized by age fifteen, 77% by eighteen, 90% by twenty-one, and 96% by twenty-four. These estimates demonstrate considerable variation and depend on the study’s model and stabilization criterion; they do not establish eighteen as a biological endpoint. (pmc.ncbi.nlm.nih.gov)

New onset and continued progression also occur in young adults. In Samantha Sze-Yee Lee and colleagues’ 2022 report from the Western Australian Raine Study, examinations at approximately ages twenty and twenty-eight showed an eight-year myopia incidence of 14% among participants initially without myopia. Across the examined cohort, 38% experienced a myopic shift of at least 0.50 D in one or both eyes. Mean refractive change was approximately −0.04 D per year, substantially slower than typical childhood progression. The distinction between incidence among initially nonmyopic participants and refractive change across the whole cohort is important: becoming myopic and becoming more myopic are separate life-course outcomes. (pmc.ncbi.nlm.nih.gov)

Refractive progression, measured in diopters, and axial elongation, measured in millimeters, are related but not interchangeable. Refraction reflects the combined effects of eye length, corneal power, and crystalline-lens power; changing optical components can partly compensate for continued growth. A 2018 COMET analysis found that axial length stabilized later than refraction in both its younger and older progressing groups: mean ages were 16.5 versus 14.3 years and 16.2 versus 15.5 years, respectively. Its axial stabilization criterion was an annual modeled increase below 0.06 mm, based on measurement variability. Another 11.2% of participants had not reached axial stabilization after fourteen years of observation. An apparently stable prescription therefore does not necessarily indicate complete cessation of ocular elongation. (pmc.ncbi.nlm.nih.gov)

Later-life refractive changes need not represent renewed axial growth. In the Beaver Dam Eye Study, examinations conducted between 1988 and 2010 showed an overall shift toward more positive refraction through much of middle age, followed by a myopic shift after approximately seventy. A 2018 analysis identified nuclear cataract as the principal contributor to the latter pattern: participants with nuclear cataract shifted approximately −0.25 D over five years, whereas those with mild or moderate nuclear sclerosis shifted approximately +0.22 to +0.23 D. These lens-associated changes distinguish an increasingly negative prescription in an older adult from the predominantly axial progression characteristic of childhood myopia. (pmc.ncbi.nlm.nih.gov)

Eye growth and biological mechanisms

Emmetropization is the developmental coordination of ocular optical power and axial length, bringing distant images into focus on the retina without accommodation. During infancy, axial growth occurs alongside changes in corneal curvature and crystalline-lens power; normal enlargement therefore need not produce myopia. Experimental studies show that visual feedback regulates this matching process. Negative lenses place the image plane behind the retina—hyperopic defocus—and generally accelerate elongation in young animals; positive lenses produce myopic defocus, with the image plane in front of the retina, and generally slow elongation. Compensation is strongest early in development, although older animals retain some responsiveness. (pmc.ncbi.nlm.nih.gov)

Evidence for local control comes from experiments in chicks and other species in which growth responses persist after optic-nerve section, showing that communication with the brain is not indispensable for these responses. Restricting visual deprivation or defocus to one retinal region can produce regional changes in eye shape rather than uniform enlargement. Peripheral retinal signals can also influence axial length and central refraction. These findings distinguish visual regulation of ocular growth from accommodation: changing the eye’s dimensions is not simply a consequence of the muscular effort used to focus. (pmc.ncbi.nlm.nih.gov)

A proposed signaling sequence runs from the retina through the retinal pigment epithelium and choroid to the sclera. Defocus-dependent changes in gene expression and biochemical activity support this model, but the complete sequence has not been established. Retinoic acid, nitric oxide, and growth factors are candidate mediators rather than components of a single proven human pathway. The sclera’s extracellular matrix is a downstream target: fibroblasts alter the synthesis, degradation, and organization of collagen and proteoglycans, changing the mechanical properties of the eye’s outer coat. In tree-shrew experiments, matrix remodeling accompanies increased scleral “creep,” meaning progressive extension under sustained load; this may permit ordinary intraocular pressure to enlarge the vitreous chamber. (myopiainstitute.org)

Such remodeling is active rather than merely passive stretching. A 2000 tree-shrew study found that form-deprivation myopia was accompanied by a $36\% \pm 7\%$ reduction in glycosaminoglycan synthesis at the posterior sclera and a $3.7\% \pm 1.2\%$ reduction in scleral dry weight relative to fellow control eyes. After deprivation ended, synthesis increased within 24 hours; after three days of recovery it was $79\% \pm 15\%$ above control-eye levels, returning to control values after nine days. These reversible metabolic responses connect altered visual input with structural changes, without establishing identical responses in human childhood myopia. (pubmed.ncbi.nlm.nih.gov)

Retinal dopamine is an important experimental link between illumination and growth regulation. In a 2010 study, Regan Ashby and Frank Schaeffel exposed chicks to 15,000 lux rather than 500 lux. Bright illumination for five hours daily slowed compensation to negative lenses and accelerated compensation to positive lenses without changing the eventual compensatory endpoint. It also reduced form-deprivation myopia by approximately 60%; intravitreal administration of the dopamine-receptor antagonist spiperone abolished that protective effect. This supports dopamine involvement in this chick model, but does not establish that dopamine alone explains the association between outdoor exposure and reduced myopia onset in children. (pubmed.ncbi.nlm.nih.gov)

The choroid also responds dynamically to visual stimuli. Josh Wallman and colleagues demonstrated defocus-related changes in chick choroidal thickness in 1995: thickening can move the retina forward toward an image plane, while thinning moves it backward. Choroidal responses may additionally influence signals reaching the sclera. Human experiments have detected much smaller short-term thickness changes, commonly about 5–30 micrometers, with responses also affected by time of day, illumination, and other physiological conditions. The 2023 International Myopia Institute report led by Lisa Ostrin found insufficient evidence to treat brief choroidal thickening as a validated predictor of subsequent slowing of axial elongation. (pmc.ncbi.nlm.nih.gov)

Genetic susceptibility and inherited forms

Myopia aggregates in families, but parental myopia captures both inherited susceptibility and shared environments. In the Avon Longitudinal Study of Parents and Children, the number of myopic parents and a genetic score based on 149 variants independently predicted childhood refractive error; together they explained 7.0% of its variance at age 15. Genetic contributions are also evident in twin studies: Christopher Hammond and colleagues reported in 2001 that additive genetic effects accounted for approximately 84–86% of variation in spherical-equivalent refraction among 506 twin pairs aged 49–79 years. Such heritability estimates describe variation within a particular population and environment, not the proportion of an individual’s myopia “caused by genes.” Estimates depend on study design, age, and environmental variation; high heritability does not imply that environmental changes cannot alter population prevalence. (pubmed.ncbi.nlm.nih.gov)

Common myopia has a predominantly polygenic architecture: many variants contribute individually small effects rather than following a single Mendelian inheritance pattern. Genome-wide association studies test variants across the genome against measured refraction, myopia status, or related traits. In 2020, Pirro Hysi and colleagues analyzed 542,934 participants of European ancestry and identified 449 associated genomic regions, including 336 previously unreported regions. Axial length provides a complementary anatomical phenotype: Chen Jiang and colleagues’ 2023 multiethnic analysis of 19,420 adults identified 16 associated loci, five of them novel, with candidates including BMP3, RGR, and RBFOX1. The study estimated a genetic correlation of 0.80 between axial length and myopia, indicating substantial, but incomplete, overlap in their inherited determinants. (pmc.ncbi.nlm.nih.gov)

Association does not establish which variant is causal, which nearby gene mediates its effect, or how that effect changes eye growth. The International Myopia Institute’s 2025 genetics report noted that most associated loci still lacked functional validation. Experimental follow-up provides stronger mechanistic evidence in selected cases. GJD2, for example, encodes the neuronal gap-junction protein connexin-36. A 2021 zebrafish study found that loss of its ortholog gjd2a reduced axial length, produced hyperopia, and altered retinal electrical responses. These findings support a role for retinal intercellular communication in refractive development, but disrupting a gene in an animal does not by itself establish the mechanism of a common human risk variant near that gene. (myopiainstitute.org)

Rare inherited forms differ from this usual architecture. A pathogenic variant in a single gene can produce early-onset or high myopia, either as a predominantly ocular condition or within a broader syndrome. Examples include ARR3-associated myopia, retinal signaling disorders involving CACNA1F, NYX, or TRPM1, and connective-tissue disorders such as Marfan syndrome (FBN1), Stickler syndrome (COL2A1), and Knobloch syndrome (COL18A1). These conditions connect refractive abnormalities to defects in phototransduction, ocular development, or collagen and extracellular-matrix organization. The 2025 report summarized diagnostic yields of approximately 12–23% for whole-exome sequencing with ocular-disorder gene panels in selected high-myopia cohorts; yield varied with patient selection and panel composition. High myopia alone therefore does not establish a monogenic cause. (myopiainstitute.org)

Gene–environment interaction means that a variant’s association with refraction differs according to exposure. Rosie Clark and colleagues’ 2022 UK Biobank study identified evidence of education-dependent effects for variants near GJD2, RBFOX1, LAMA2, KCNQ5, and LRRC4C: university education was associated with larger effects of the myopia-predisposing alleles. The analysis used separate samples of 88,334 and 252,838 participants. Education was nevertheless a broad exposure indicator, not a direct measurement of near viewing or outdoor light; the biological pathways underlying these interactions remained unresolved. These results distinguish statistical interaction from a demonstrated molecular response to a specific environmental stimulus. (pubmed.ncbi.nlm.nih.gov)

Polygenic risk scores combine variant counts weighted by GWAS-derived effect estimates. A study published online in 2019 and in a 2020 journal issue validated such a score in 1,516 adults, obtaining areas under the receiver-operating-characteristic curve of 0.67 for myopia and 0.73 for high myopia, defined there as spherical equivalent ≤−5.00 D. This was adult classification, not prospective prediction of childhood onset. Performance depends on ancestry, phenotype definition, and validation population; a score developed in one ancestry group may transfer poorly to another. Although later models incorporated environmental and demographic information, the 2025 International Myopia Institute report still described these scores as research tools rather than clinically established tests. (pmc.ncbi.nlm.nih.gov)

Environmental and educational influences

Longer and more intensive education is associated with more myopic refraction, but years of schooling combine several exposures: close viewing, examinations, indoor study, and reduced outdoor time. Evidence extending beyond observational correlation comes from Edward Mountjoy and colleagues’ 2018 study of 67,798 UK Biobank participants. Using Mendelian randomization, which treats genetic variants associated with educational duration as instrumental variables, they estimated a refractive shift of −0.27 diopters per additional year of education, with a 95% confidence interval of −0.37 to −0.17 diopters. The reverse analysis found little evidence that myopic refraction increased educational duration. This supports a causal contribution from education-related exposures, without identifying which classroom practices mediate it; interpretation also depends on assumptions that the genetic instruments do not affect refraction through independent pathways. (bmj.com)

Near work includes reading, writing, and other activities performed at short viewing distances. Associations with total reported near-work duration are generally weaker and less consistent than those with education. Viewing patterns may matter independently of accumulated hours: Jenny Ip and colleagues’ 2008 Sydney Myopia Study analysis found that reading at less than 30 cm and reading continuously for more than 30 minutes were associated with higher odds of myopia among 12-year-olds, whereas total near-work time was not independently associated after adjustment. These were observational associations, not experimentally established distance or duration thresholds. Close viewing increases accommodation demand, and accommodative lag has been proposed to produce growth-promoting hyperopic retinal defocus; however, this pathway is not established as the principal explanation for human school-age myopia. Questionnaire estimates also poorly capture actual viewing distance, interruptions, and changes in behaviour before onset. (pubmed.ncbi.nlm.nih.gov)

Outdoor exposure is associated particularly with lower childhood myopia incidence, rather than simply with less sedentary behaviour. Kathryn Rose and colleagues’ 2008 Sydney study found lower myopia prevalence among 12-year-olds reporting more outdoor time, including both sport and leisure; indoor sport showed no corresponding association. Thus, physical activity and outdoor exposure are not interchangeable variables. Stronger evidence came from Mingguang He and colleagues’ school-cluster randomized controlled trial, published in 2015: adding a 40-minute outdoor class each school day, together with encouragement of outdoor activities at home, reduced three-year cumulative incidence among initially nonmyopic Guangzhou pupils from 39.5% to 30.4%, an absolute difference of 9.1 percentage points. This onset-prevention result does not by itself establish comparable slowing of already established myopia. Higher outdoor illuminance and light-dependent retinal signaling, including dopamine, are proposed explanations, but the relative contributions of these mechanisms in children remain unresolved. (pubmed.ncbi.nlm.nih.gov)

Digital-device use overlaps with near work and may displace outdoor exposure, making a screen-specific effect difficult to isolate. Ahnul Ha and colleagues’ 2025 meta-analysis included 45 studies and 335,524 participants; each additional daily hour of screen use was associated with 21% higher odds of myopia. Between-study heterogeneity was very high, with $I^2=99.0\%$, and the pooled incidence-only association was not statistically significant. The overall estimate therefore should not be interpreted as a 21% increase in an individual child’s probability of developing myopia. Devices viewed at different distances, educational and recreational use, self-reported exposure, and incomplete adjustment for outdoor time or conventional reading further complicate interpretation. The association does not establish that screen-emitted light itself causes myopic eye growth. (jamanetwork.com)

Urbanization and socioeconomic circumstances are broader exposure bundles rather than single biological causes. In a 2008 Sydney study, myopia prevalence among 12-year-olds ranged from 6.9% in outer suburban areas to 17.8% in the inner city, and regional differences persisted after adjustment for several measured factors. Such residual associations can reflect unmeasured educational intensity, housing conditions, outdoor opportunities, or measurement error rather than an independent effect of population density. Income and parental education likewise correlate with schooling and lifestyle, while parental myopia can represent both inherited susceptibility and shared family environments. Statistical adjustment reduces measured confounding but cannot eliminate unmeasured confounding or determine whether an adjusted variable is itself part of the causal pathway. Consequently, causal inference is stronger when observational patterns converge with longitudinal evidence, natural experiments, genetic instrumental-variable analyses, or randomized changes in exposure. (pubmed.ncbi.nlm.nih.gov)

Symptoms and visual function

Distance blur is the characteristic symptom of myopia: fine details on a classroom board, road signs, or distant faces become difficult to distinguish, while nearby objects may remain clear. The underlying optical defocus spreads the image of each point across the retina rather than forming a sharply focused image, reducing the visibility of edges and detail. Squinting can temporarily make distant objects appear clearer. Other reported symptoms include eyestrain—experienced as tired or sore eyes—and, less commonly, headaches. Neither eyestrain nor headache is specific to myopia; similar complaints occur in disorders of binocular coordination, including convergence insufficiency. Their presence alone therefore does not establish the cause of blurred vision. (nei.nih.gov)

Mild myopia may produce no recognized symptoms, particularly when everyday activities do not demand fine distance vision. Children may not realize that their vision is reduced and therefore may not report difficulty seeing. Reading material held nearby can remain clear even when writing across a classroom is blurred, so successful near work does not demonstrate normal distance vision. Unequal vision between the eyes can further conceal a problem: children with different refractive errors in the two eyes may keep both eyes open and make no complaint because the better-seeing eye compensates. Consequently, reported symptoms and measured visual function can differ substantially. (nei.nih.gov)

Unaided visual acuity describes the ability to resolve detail without spectacles or contact lenses. Presenting acuity describes vision with whatever correction is habitually worn, whereas best-corrected visual acuity describes the best result obtainable with an appropriate optical correction. These measures answer different questions: poor unaided acuity may reflect correctable defocus, while reduced best-corrected acuity indicates that optical correction does not fully account for the impairment. In Snellen notation, 20/40 means that the observer resolves at 20 feet a detail that a reference observer resolves at 40 feet; it does not mean “half of normal vision.” Acuity is also distinct from refractive power: an acuity result describes visual performance, not the lens prescription itself. (ncbi.nlm.nih.gov)

Chart acuity is only one component of everyday visual performance. Standard clinical charts generally use stationary, high-contrast targets under controlled lighting, whereas ordinary tasks involve varying illumination, contrast, viewing distance, and movement. Contrast sensitivity describes the ability to detect differences in brightness between a target and its background. Refractive defocus can reduce this sensitivity as well as fine-detail resolution. Low illumination and glare can make visual tasks more difficult than a well-lit chart result suggests; recognizing a faded sign at dusk, for example, is not equivalent to reading black letters on a white chart. Thus, identical chart-acuity scores need not imply identical performance under all viewing conditions. (ncbi.nlm.nih.gov)

In uncomplicated myopia, the principal functional limitation is refractive blur, which optical correction can substantially resolve. Vision loss associated with ocular disease differs because damage to retinal or neural structures may remain after the image is focused correctly. The International Myopia Institute’s 2019 definition of pathologic myopia explicitly includes structural changes that can cause loss of best-corrected visual acuity. Separately, amblyopia involves abnormal visual development and may also limit corrected vision. A stronger negative prescription and a lower best-corrected acuity therefore describe different aspects of the eye’s condition: the former measures refractive error, while the latter may reflect additional disease or developmental impairment. (ncbi.nlm.nih.gov)

Diagnosis and ocular assessment

Visual-acuity testing documents distance vision separately in each eye, both without correction and with the best available refractive correction. Letter charts are used in children who can identify letters; matching tests with standardized symbols, such as LEA symbols or HOTV letters, permit assessment in younger children. Chart distance, illumination, and whether symbols are presented singly or surrounded by other symbols affect comparability. Acuity testing identifies reduced vision but does not measure the refractive error itself. A comprehensive assessment also records the age at onset, previous prescriptions, ocular and general medical history, and family history, alongside examination of ocular alignment, accommodation, and anterior-eye health. (pmc.ncbi.nlm.nih.gov)

Objective refraction can be measured by retinoscopy or autorefraction. In retinoscopy, the examiner sweeps light across the pupil and observes the movement of the reflected retinal light, introducing lenses until the reflex is neutralized and accounting for the examination working distance. Because this method does not require judgments about image clarity, it is particularly useful in young children. Autorefractors provide instrument-derived estimates of spherical and cylindrical power and cylinder axis. Open-field instruments allow fixation on an external distant target, reducing instrument-induced accommodation compared with enclosed viewing systems. Subjective refraction subsequently refines lens power through the patient’s comparisons of clarity, establishing the correction that provides the best visual acuity without unnecessary minus power. (eyewiki.aao.org)

Cycloplegic refraction temporarily suppresses accommodation with topical medication, separating the eye’s resting refractive state from focusing responses during testing. This is especially important in children, whose accommodation can make measurements more negative, exaggerate existing myopia, or classify an emmetropic or hyperopic eye as myopic. The 2025 International Myopia Institute instrumentation report, led by Deborah Jones, described noncycloplegic measurements in myopic children as averaging approximately 0.6–0.8 diopters more myopic than cycloplegic measurements; differences were larger and more variable in children without myopia. Cyclopentolate and tropicamide are commonly used agents. Pupil dilation alone does not establish that accommodation has been adequately suppressed, and serial measurements require comparable examination conditions. (doi.org)

Axial-length biometry measures the eye’s anteroposterior dimension and provides a structural measure of growth alongside refraction. Noncontact optical instruments use partial-coherence interferometry, optical low-coherence reflectometry, or swept-source optical coherence tomography; A-scan ultrasonography instead derives distances from acoustic echoes. The 2025 instrumentation report summarized pediatric repeatability, expressed as a standard deviation, of approximately 0.02–0.06 mm for interferometry and reflectometry, and 0.01–0.05 mm for OCT-based biometry, depending on the instrument. Such measurement uncertainty matters when interpreting small longitudinal changes. Multiple readings and their variability help distinguish growth from measurement noise. Corneal topography maps the anterior surface, whereas tomography reconstructs anterior and posterior surfaces and corneal thickness; these measurements help characterize corneal shape and document changes associated with contact-lens fitting or corneal reshaping. (doi.org)

Dilated fundus examination assesses the optic nerve, macula, and peripheral retina for abnormalities that refraction cannot reveal. The 2019 International Myopia Institute clinical-management report, chaired by Kate Gifford, specified annual dilated central and peripheral retinal examination in high myopia, with examination in other patients according to clinical indications. Retinal photography supplies a reproducible record of visible findings for comparison over time. Optical coherence tomography provides cross-sectional structural imaging and helps detect or monitor myopia-associated retinal abnormalities. Enhanced-depth imaging can also measure the choroid, although the clinical-management role of choroidal thickness as a progression marker remained undefined in the 2025 instrumentation summary. (doi.org)

Secondary myopia and differential diagnosis

The International Myopia Institute’s 2019 report, led by Ian Flitcroft, defines secondary myopia as a myopic refractive state attributable to a specific cause—such as a drug, corneal disease, or systemic syndrome—rather than to a recognized population risk factor such as educational exposure. Secondary myopia may result from excessive axial length, altered corneal or lens power, or a combination of these mechanisms; it is not necessarily transient. Pseudomyopia, by contrast, is an apparent myopic shift caused by excessive accommodation: the ciliary muscle fails to relax fully during distance viewing, maintaining increased lens power. Cycloplegic refraction, which pharmacologically relaxes accommodation, reduces or abolishes this component. Persistent myopia remains after accommodation is relaxed, although persistent myopia and an additional accommodative component can coexist. A difference between non-cycloplegic and cycloplegic measurements must be interpreted in context, because some difference occurs normally, particularly in children. (pmc.ncbi.nlm.nih.gov)

Corneal and lenticular abnormalities can produce a strongly negative prescription without proportionate axial elongation. In keratoconus, progressive corneal thinning and outward protrusion alter corneal curvature, producing myopia and astigmatism; irregular optical distortion may limit spectacle-corrected acuity. Microspherophakia, a developmental abnormality in which the lens is unusually small and spherical, is another recognized cause of secondary myopia. Nuclear cataract can cause a myopic shift through changes in the lens’s refractive index, rather than continued eye growth. A 2008 longitudinal report from the Blue Mountains Eye Study found mean ten-year refractive changes of −0.96 D in eyes with baseline nuclear cataract and +0.26 D in eyes without it. Such lens-related changes distinguish a newly more negative prescription in an older adult from ordinary axial progression. (nei.nih.gov)

Medication-associated myopia provides a particularly clear example of an identifiable secondary cause. Topiramate, used for epilepsy and migraine prevention, can produce supraciliary or ciliochoroidal effusion, anterior displacement of the lens–iris diaphragm, and shallowing of the anterior chamber. The resulting myopic shift can accompany secondary angle-closure glaucoma, a mechanism distinct from excessive accommodation or axial elongation. U.S. prescribing information describes onset typically within one month of starting treatment and documents occurrence in both children and adults. Acute bilateral distance blur, ocular pain, and a recent medication exposure therefore form a different diagnostic pattern from gradually developing school-age myopia. Changes in lens refraction associated with diabetes mellitus are another potential cause of transient refractive shifts and should not automatically be classified as pseudomyopia. (dailymed.nlm.nih.gov)

High myopia in infancy or early childhood has a different distribution of causes from typical school-age myopia. The 2023 International Myopia Institute report found high myopia uncommon in preschool children, with prevalence below 1%, but emphasized the comparatively frequent involvement of prematurity and genetic disorders. Retinopathy of prematurity can be associated with myopia that is not primarily axial. Other diagnostic possibilities include Stickler and Marfan syndromes, inherited retinal dystrophies, developmental corneal or lens abnormalities, and congenital glaucoma. Birth history, family history, systemic features, ocular biometry, and anterior-segment and retinal findings help distinguish these conditions. For example, congenital myopia accompanied by abnormal vitreous structure and hearing or skeletal abnormalities is a different clinical pattern from isolated myopia beginning during school years. (pmc.ncbi.nlm.nih.gov)

Reduced distance acuity is not, by itself, evidence that refractive error accounts for all visual impairment. Uncomplicated myopic blur improves with accurate optical correction; persistent reduction in best-corrected acuity raises the differential of amblyopia, corneal or lens opacity, retinal disease, and other ocular abnormalities. Amblyopia reflects abnormal visual development, potentially following unequal refractive errors, severe uncorrected bilateral refractive error, strabismus, or deprivation from childhood cataract; it cannot be identified merely from prescription strength. Retinal dystrophy may coexist with high myopia, with impaired colour vision or other retinal findings providing additional clues. Assessment therefore separates the measurable refractive error from the cause of any residual loss of visual function. (nei.nih.gov)

Spectacles and contact-lens correction

Diverging spectacle lenses compensate for the excessive optical power of a myopic eye relative to its length. Their negative power makes incoming rays less convergent before they enter the cornea, moving the image focus backward from in front of the retina onto the retinal surface. This correction changes the refraction of entering light rather than the eye’s anatomical dimensions. A single-vision prescription supplies one distance-correction power, with a cylindrical component when astigmatism also requires correction; it does not incorporate a separate near-addition zone. Spectacles improve vision while worn but do not permanently eliminate the underlying refractive error. (nei.nih.gov)

Spectacles and contact lenses differ partly because of their position relative to the eye. Spectacle lenses sit in front of the cornea, whereas contact lenses rest on the tear-covered ocular surface and move with the eye. Strong negative spectacle lenses produce retinal-image minification, which is substantially reduced with contact lenses; contact lenses can also provide a wider unobstructed field of view. These differences become more noticeable with stronger prescriptions, but contact lenses do not invariably produce better visual performance: lens material, optical design, and the viewing task also affect the comparison. The separation between a spectacle lens and the cornea, called vertex distance, affects its effective power, so stronger spectacle prescriptions cannot simply be transferred unchanged to contact lenses. Contact-lens fitting calculations account for this difference. (sciencedirect.com)

Restoring a sharp retinal image is a different outcome from slowing axial elongation. Conventional single-vision spectacles and contact lenses correct distance blur but are not equivalent to optical designs specifically developed for myopia control. In a three-year randomized controlled trial published in 2008, Jeffrey J. Walline and colleagues assigned 484 children aged 8–11 years, with prescriptions between −1.00 and −6.00 diopters, to ordinary soft contact lenses or spectacles. The contact-lens group had a small additional refractive change averaging 0.06 diopters per year, but no statistically significant difference in axial-length change. Thus, changing the mode of ordinary correction did not demonstrate a meaningful reduction in eye growth. Specialized multifocal or dual-focus lenses have a different purpose, combining correction with an optical intervention intended to alter progression. (pubmed.ncbi.nlm.nih.gov)

Contact-lens fitting requires more information than refractive power alone. Relevant specifications include lens material or manufacturer, base curve, and diameter; toric lenses additionally require assessment of rotational stability because rotation changes the alignment of astigmatic correction. Soft lenses and rigid gas-permeable lenses differ in handling and adaptation: soft lenses are generally easier to adjust to, whereas rigid lenses may require a longer adaptation period. These fitting and tolerance constraints mean that identical nominal powers do not make different contact-lens products interchangeable. (fda.gov)

Documented adverse events include irritation, conjunctivitis, corneal abrasions, and microbial keratitis, an infection that can produce corneal ulceration, scarring, and permanent loss of vision. Water exposure has been associated with Acanthamoeba infection. In a 2018 report, Jennifer R. Cope and colleagues described six corneal infections associated with sleeping in contact lenses; some required surgical intervention or resulted in permanent damage. The report cited a six- to eightfold increase in infection risk associated with sleeping in lenses, including prescribed extended wear. Separately, an analysis of 1,075 contact-lens-related infection reports submitted to the US Food and Drug Administration during 2005–2015 found that 19.8% described eye damage. Because this was a passive adverse-event reporting database rather than a representative cohort of wearers, that percentage does not estimate the probability of damage among all contact-lens users or all infections. (fda.gov)

Refractive surgery

Corneal refractive procedures correct myopia by flattening the central cornea and reducing its focusing power. In photorefractive keratectomy (PRK), the surface epithelium is removed and an excimer laser ablates underlying stromal tissue; the epithelium subsequently regenerates. In laser-assisted in situ keratomileusis (LASIK), a femtosecond laser or mechanical microkeratome creates a hinged corneal flap, which is lifted for excimer-laser ablation of the exposed stroma and then repositioned. PRK therefore involves surface healing, whereas LASIK introduces a persistent flap interface. Small-incision lenticule extraction (SMILE) uses a femtosecond laser to delineate a lens-shaped piece of tissue within the stroma; surgical removal through a small incision changes corneal curvature without creating a LASIK-type flap. These procedures alter optical power rather than the length of the eyeball. (fda.gov)

Lens-based correction changes the eye’s internal optical system. A phakic intraocular lens is implanted in front of or behind the iris while retaining the natural crystalline lens. Retention preserves the anatomical mechanism of accommodation, distinguishing this approach from lens replacement. Phakic lenses can correct substantial myopia without removing corneal tissue, although their suitability depends on internal eye dimensions and other findings. Refractive lens exchange removes the natural lens and replaces it with an artificial intraocular lens, using essentially the same operation as cataract surgery but primarily to change refraction. Removal permanently eliminates natural-lens accommodation; multifocal implants provide more than one optical focus rather than restoring that physiological process. Lens exchange also carries intraocular surgical risks, including infection, capsular rupture, and retinal detachment, with particular relevance to highly myopic eyes. (fda.gov)

Preoperative assessment establishes refractive stability, achievable corrected vision, and procedure-specific anatomical limits. Stability is documented through previous prescriptions and repeated refraction measurements rather than inferred solely from age. For example, the FDA’s 2016 approval of the original VisuMax SMILE indication required patients to be at least 22 years old and to have a spherical-equivalent change of no more than 0.50 diopters during the preceding year. Corneal assessment includes thickness, curvature mapping, and screening for keratoconus or other abnormalities that increase the risk of postoperative weakening. Examination also considers tear-film disease, pupil size under dim illumination, and coexisting lens, retinal, or optic-nerve disease. Phakic-lens assessment additionally measures anterior chamber depth and corneal endothelial cell density, because inadequate space or a low cell count increases complication risks. (accessdata.fda.gov)

Documented adverse outcomes include residual refractive error, regression, dry-eye symptoms, glare, halos, double images, and reduced vision under low-contrast conditions. Some patients lose best-corrected visual acuity: the postoperative deficit cannot be eliminated by spectacles or contact lenses. In the FDA-associated Patient-Reported Outcomes with LASIK studies, published in 2017, up to 46% of participants without preoperative visual symptoms reported at least one new visual symptom three months after surgery, and up to 28% without preoperative dry-eye symptoms reported new dryness. Nevertheless, more than 95% reported satisfaction with their vision; fewer than 1% reported substantial difficulty or inability to perform usual activities because of any single visual symptom. These short-term LASIK findings do not establish equivalent rates for PRK, lenticule extraction, or lens-based procedures. Phakic implants have additional documented risks, including endothelial cell loss, cataract formation, increased intraocular pressure, and implant repositioning or removal. (fda.gov)

A postoperative refraction near zero does not mean that the anatomical basis of axial myopia has disappeared. Corneal reshaping or lens implantation compensates optically for an elongated eye but does not shorten it or reverse existing posterior-segment damage. Consequently, successful correction of distance blur does not remove the structural risks associated with high myopia, including retinal detachment. Refractive lens exchange can add a further retinal-detachment risk through lens removal itself; this is distinct from the risk already associated with the myopic eye. (fda.gov)

Interventions to delay onset and slow progression

Interventions address three distinct outcomes: delaying the first occurrence of myopia in a nonmyopic child, slowing the subsequent negative shift in spherical-equivalent refraction, and reducing axial elongation. The latter two are measured in diopters (D) and millimeters (mm), respectively, and need not show equivalent treatment effects. Ordinary single-vision correction restores clarity but is not itself a progression-control intervention. Reduced myopia incidence during a trial demonstrates delayed onset over that observation period, not necessarily lifelong prevention. Most intervention evidence concerns children rather than adults. (pmc.ncbi.nlm.nih.gov)

Specialized spectacles combine distance correction with additional optical elements intended to alter retinal defocus or image contrast. Defocus incorporated multiple segments (DIMS) lenses surround a central corrective zone with segments having +3.50 D of relative positive power; other designs use highly aspherical lenslets or contrast-modifying elements. In Carly Lam and colleagues’ two-year randomized controlled trial, published in 2019, children aged 8–13 wearing DIMS lenses had mean refractive progression of −0.41 D and axial elongation of 0.21 mm, compared with −0.85 D and 0.55 mm with single-vision spectacles. These designs modify the visual signals implicated in eye growth while retaining distance correction; their precise biological mechanisms remain incompletely established. (pmc.ncbi.nlm.nih.gov)

Multifocal and dual-focus soft contact lenses similarly combine distance-correcting regions with additional positive-power regions. In the 2020 BLINK trial, involving children aged 7–11, high-add multifocal lenses produced an adjusted three-year treatment difference of 0.46 D less progression and 0.23 mm less axial elongation than single-vision contact lenses. Orthokeratology instead uses overnight reverse-geometry rigid lenses to flatten the central cornea and steepen the mid-periphery, temporarily correcting daytime vision and altering peripheral optics. Pauline Cho and Sin-Wan Cheung’s 2012 ROMIO trial recorded two-year axial elongation of 0.36 mm with orthokeratology versus 0.63 mm with single-vision spectacles. Axial length is particularly important here because corneal reshaping changes refraction independently of eye growth. Contact-lens interventions carry ocular-surface and microbial-keratitis risks, especially with overnight wear. (pmc.ncbi.nlm.nih.gov)

Atropine is a muscarinic-receptor antagonist whose growth-inhibiting action is not explained simply by paralysis of accommodation. Effects depend partly on concentration: Jason Yam and colleagues’ 2019 LAMP trial reported one-year refractive changes of −0.27, −0.46, and −0.59 D with nightly 0.05%, 0.025%, and 0.01% atropine, respectively, versus −0.81 D with placebo; corresponding axial elongation was 0.20, 0.29, 0.36, and 0.41 mm. Pupil dilation and reduced accommodation can cause light sensitivity and near blur, with allergic reactions also reported. Rebound—accelerated progression after withdrawal—varies with concentration and age. In LAMP’s 2022 discontinuation study, stopping 0.05% atropine yielded third-year progression of −0.68 D and elongation of 0.33 mm, compared with −0.28 D and 0.17 mm during continued treatment; younger age was associated with greater rebound. (pure.eur.nl)

Outdoor-time interventions have clearer evidence for reducing onset than for slowing established myopia. Mingguang He and colleagues’ 2015 Guangzhou school trial added a 40-minute outdoor class each school day and encouraged outdoor activity at home: three-year myopia incidence was 30.4%, versus 39.5% under usual activity. Evidence for a comparable effect in already-myopic children is less consistent. Pharmacological onset delay was demonstrated in the 2023 LAMP2 trial: among initially nonmyopic children aged 4–9, two-year incidence was 28.4% with 0.05% atropine, 45.9% with 0.01%, and 53.0% with placebo. The 0.01%–placebo difference was not statistically significant. (pubmed.ncbi.nlm.nih.gov)

Combination studies test whether optical and pharmacological interventions provide additional effects. The International Myopia Institute’s 2025 review identified five randomized trials combining orthokeratology with 0.01% atropine, with a median additional reduction in two-year axial elongation of 0.12 mm relative to orthokeratology alone. Such findings do not establish that every combination is additive or synergistic. Outcomes vary with age, baseline refraction, lens design, drug concentration, adherence, and observation period; differences between separate trials cannot by themselves establish comparative superiority. (myopiainstitute.org)

Pathologic myopia and associated eye disease

Pathologic myopia denotes structural damage in the posterior eye, rather than simply a strong negative prescription. Its defining lesions include posterior staphyloma or myopic maculopathy at least as severe as diffuse chorioretinal atrophy; no fixed refractive-error or axial-length threshold is required. A posterior staphyloma is a localized outward bulge of the eye wall whose radius of curvature is smaller than that of the surrounding wall, distinguishing it from generalized axial elongation. Associated changes include thinning of the sclera and choroid, retinal degeneration, and deformation around the optic nerve. In a 2021 imaging study of 237 highly myopic eyes, eyes with staphyloma had thinner choroidal and scleral tissues than those without it. These anatomical differences are relevant to complications that persist despite correction of refractive blur. (pmc.ncbi.nlm.nih.gov)

Myopic maculopathy encompasses atrophic and neovascular lesions affecting central vision. The META-PM classification, published in 2015 by Kyoko Ohno-Matsui and colleagues, grades fundus photographs from category 0, no myopic retinal lesions, through category 1, tessellation; category 2, diffuse chorioretinal atrophy; category 3, patchy atrophy; and category 4, macular atrophy. Lacquer cracks, myopic macular neovascularization, and Fuchs spots are additional “plus” lesions. Lacquer cracks are yellowish linear lesions representing healed breaks in the retinal pigment epithelium–Bruch’s membrane–choriocapillaris complex. Their formation can produce subretinal hemorrhage without neovascularization. Neovascular lesions involve abnormal vessels beneath the retina and may subsequently leave a pigmented scar, termed a Fuchs spot, with surrounding atrophy. (scholars.duke.edu)

Myopic traction maculopathy results from mechanical forces involving the vitreous, surface membranes, and the deformed posterior eye wall. Its manifestations include retinoschisis, in which retinal layers split internally; localized foveal detachment; and partial- or full-thickness macular holes. Optical coherence tomography distinguishes these configurations. Retinoschisis is not synonymous with retinal detachment: the former separates layers within the retina, whereas the latter separates the neurosensory retina from the underlying retinal pigment epithelium. Nevertheless, a full-thickness macular hole can permit fluid to pass beneath the retina and cause detachment. Highly myopic eyes can also develop detachment from peripheral retinal breaks, independently of macular traction. (pmc.ncbi.nlm.nih.gov)

High myopia is associated with glaucoma and cataract, although neither complication alone defines pathologic myopia. In the Beijing Eye Study’s 2001–2011 follow-up, open-angle glaucoma developed in 13.3% of the high-myopia group, compared with 2.1% of the emmetropic/hyperopic group; the reported odds ratio was 7.3. Glaucoma assessment is complicated by myopic optic-disc deformation, peripapillary atrophy, and visual-field defects caused by macular disease, which can resemble or obscure glaucomatous damage. A 2013 report from the Blue Mountains Eye Study associated high myopia with increased 10-year incidence of nuclear cataract, with an adjusted odds ratio of 3.01, and posterior subcapsular cataract, with an odds ratio of 7.80. These are population associations, not individual predictions. (pubmed.ncbi.nlm.nih.gov)

Treatment targets particular complications rather than reversing ocular elongation. Intravitreal drugs inhibiting vascular endothelial growth factor suppress active myopic neovascularization. In the 2014 RADIANCE randomized trial of 277 patients, two ranibizumab regimens produced average gains of 10.5 and 10.6 visual-acuity chart letters over months 1–3, compared with 2.2 letters after verteporfin photodynamic therapy. Existing atrophy can still limit vision. Tractional disease may be treated with vitrectomy, membrane peeling, gas tamponade, or macular buckling, which supports and reshapes the posterior wall; retinal detachment has separate reattachment procedures, including vitrectomy and scleral buckling. Glaucoma treatments lower intraocular pressure but do not restore lost nerve tissue. Neither these interventions nor refractive correction regenerate established chorioretinal atrophy. (pubmed.ncbi.nlm.nih.gov)

Public health, service access, and economic burden

The public-health burden of myopia includes two distinct forms of visual impairment. Uncorrected or inadequately corrected myopia produces optical blur that can generally be removed by an appropriate spectacle or contact-lens prescription. Myopia-associated retinal degeneration and optic-nerve damage can instead reduce best-corrected vision: changing the prescription does not reverse damaged tissue. Consequently, access to refraction and spectacles addresses one component of the burden, whereas specialist assessment, complication-specific treatment, and visual rehabilitation address another. The International Myopia Institute’s 2021 impact report also distinguished visual acuity from quality of life, which encompasses dependence on correction, limitations in daily activities, psychosocial effects, and concern about future vision. These outcomes are not captured fully by the magnitude of a spectacle prescription. (myopiainstitute.org)

Evidence linking correction to educational outcomes includes Xiaochen Ma and colleagues’ 2014 cluster-randomized controlled trial in rural western China. Conducted during the 2012–2013 school year, it enrolled 3,177 fourth- and fifth-grade children needing spectacles across 252 schools; only 15% wore spectacles at baseline. Providing free spectacles in class, rather than a prescription alone, increased observed spectacle wear at follow-up from 26% to 41% and improved mathematics scores by 0.11 standard deviations, with a 95% confidence interval of 0.01–0.21. The result demonstrated an educational benefit in that setting, although it was smaller than the prespecified effect used to calculate sample size. The voucher arm illustrates why affordability alone does not eliminate access barriers: families still paid transportation costs to a county hospital, located a median of 30 km from their townships. (bmj.com)

Service barriers include insufficient trained refraction and dispensing personnel, concentration of services in cities, reliance on private providers, out-of-pocket costs, and low public acceptance of spectacles. These barriers affect routine correction and access to the referral services required when vision remains reduced after correction. School eye-health programmes therefore involve more than identifying children who fail an acuity test: screening must connect to refraction, spectacle provision, and referral pathways. WHO’s 2024 Vision and eye screening implementation handbook describes such pathways in community and primary-care settings. Integration into the health system also requires workforce planning, financing, quality standards, and monitoring rather than isolated screening campaigns. (pmc.ncbi.nlm.nih.gov)

The World Health Organization launched SPECS 2030 in May 2024, following the World Health Assembly’s adoption of a refractive-error coverage target in 2021. Its five pillars concern services, personnel, education, costs, and surveillance. The target is a 40-percentage-point increase in effective refractive error coverage by 2030, not merely a 40% relative increase. Effective coverage concerns people whose need for correction has been met with an adequate visual result, rather than the number of spectacles distributed. The initiative addresses refractive errors collectively, so its coverage statistics should not be interpreted as myopia-specific measurements. (who.int)

Economic estimates distinguish direct expenditure from potential productivity losses. Household expenses include examinations, spectacles, contact lenses, transport, and treatment of complications. A Singapore study published in 2008, involving 377 schoolchildren aged 12–17 years, reported mean annual direct myopia costs of S$221.68 per child, equivalent to US$148 at the study’s conversion rate; the median was S$125. These historical, setting-specific values are not current prices or globally representative costs. (pubmed.ncbi.nlm.nih.gov) Kovin Naidoo and colleagues’ modeling study, published in 2019, estimated potential global productivity losses for 2015 of US$244 billion from uncorrected myopia and US$6 billion from myopic macular degeneration, with respective uncertainty intervals of US$49–697 billion and US$2–17 billion. The model combined visual-impairment estimates with disability weights, labor-force participation, employment rates, and gross domestic product per capita; spectacle coverage was modeled using development, urbanization, and age. These figures represent modeled economic output potentially lost, not measured reductions in individual wages or employment, and do not quantify children’s educational losses. (sciencedirect.com)

Development of modern myopia research

A major change in myopia research during the late twentieth century was the move from describing refractive errors and correcting their optical effects to experimentally investigating how visual experience regulates eye growth. In 1977, Torsten Wiesel and Elio Raviola reported that macaques whose eyelids had been sutured closed shortly after birth developed marked myopia and eye enlargement. Their experiment supplied an animal model in which altered visual input preceded the refractive change, allowing investigators to test mechanisms rather than rely solely on associations in human populations. Subsequent work established form deprivation—the degradation of spatial detail by eyelid closure or translucent occluders—as a reproducible experimental approach across several species. These models helped establish that postnatal ocular growth is responsive to vision, rather than being determined exclusively by an inherited growth programme. (nature.com)

Experiments then distinguished the consequences of losing a detailed image from those of imposing a particular direction of optical defocus. In 1988, Frank Schaeffel, Adrian Glasser, and Howard Howland reported that chickens wearing positive or negative lenses developed refractive changes that compensated for the lenses; eyes exposed to negative lenses had greater posterior nodal distances than those exposed to positive lenses. Lens experiments supported a feedback account of emmetropization, the developmental matching of ocular length to optical power: hyperopic defocus generally promotes elongation, whereas myopic defocus restrains it. Evidence for local control came from Josh Wallman and colleagues’ 1987 experiment with translucent occluders covering only part of the visual field. The corresponding deprived retinal region developed myopia, with a median of approximately −15 diopters, and regional vitreous-chamber elongation, while the undeprived region remained nearly emmetropic. These findings shifted attention toward retinal growth signals and provided an experimental basis for later optical-control strategies, without establishing that animal responses transfer unchanged to children. (sciencedirect.com)

Longitudinal childhood research complemented these experimental approaches by recording ocular development before, during, and after myopia onset. The US Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE study) collected data at five clinical sites between 1989 and 2010, using annual examinations that included cycloplegic autorefraction, corneal measurements, ocular dimensions measured by ultrasonography, and questionnaires about visual activities. In a 2015 analysis led by Karla Zadnik, 4,512 initially nonmyopic children were evaluated for 13 candidate predictors; 414 developed myopia during follow-up. The study defined onset as at least −0.75 diopters in each principal meridian of the right eye. Baseline spherical-equivalent refraction was the strongest single predictor, with discrimination statistics ranging from 0.87 to 0.93, and performed approximately as well as a model incorporating eight factors. The research showed that reduced age-appropriate hyperopia could precede onset. It also distinguished predictive usefulness from causation: a variable’s limited additional contribution after current refraction is included does not demonstrate that it has no etiological role. (pmc.ncbi.nlm.nih.gov)

International coordination developed alongside this methodological expansion. The joint World Health Organization–Brien Holden Vision Institute Global Scientific Meeting on Myopia took place at the University of New South Wales in Sydney on 16–18 March 2015. It addressed definitions, the burden of myopia and high myopia, evidence for interventions, and public-health responses; its report, The Impact of Myopia and High Myopia, was released in 2016. The International Myopia Institute subsequently organized expert groups to consolidate evidence and standardize terminology. Its first reports, published in 2019, covered classification, experimental models, genetics, interventions, clinical trials and instrumentation, ethical considerations, and clinical management. Further series in 2021, 2023, and 2025 extended coverage to risk factors, pathologic myopia, young-adult progression, early-childhood high myopia, ocular tissue changes, and updated intervention and genetic evidence. These publications created a shared framework for connecting laboratory findings, population research, and clinical investigation. (myopiainstitute.org)

Clinical-trial methods and evidence interpretation

Randomized controlled trials compare interventions with concurrently followed comparison groups. Concealed randomization limits selection bias and distributes potential confounders between groups; stratification can improve balance in important predictors such as age. Concurrent controls help distinguish treatment effects from the natural slowing of progression as children age and from seasonal variation. Comparators may include single-vision correction, a pharmaceutical vehicle without the active ingredient, or another active intervention. Double masking keeps participants and outcome examiners unaware of allocation, reducing behavioral and assessment bias. Participant masking is difficult in orthokeratology, where overnight lens wear differs visibly from spectacle use, but outcome examiners can still be masked. These principles were detailed in the International Myopia Institute’s (IMI) 2019 instrumentation report, led by James S. Wolffsohn. (myopiainstitute.org)

Refractive change and axial elongation are complementary outcomes, not interchangeable measurements. Change in spherical-equivalent refraction, expressed in diopters (D), measures the optical result; increasingly negative values indicate progression. Axial-length change, expressed in millimeters (mm), measures ocular elongation. Corneal or lenticular changes can alter refraction without corresponding axial growth. Orthokeratology deliberately changes corneal power, making axial length the principal progression outcome during treatment. Cycloplegic autorefraction reduces accommodation-related error, while noncontact optical biometry measures axial length. Consistent instruments, calibration, and measurement protocols limit measurement uncertainty; physiological variation in axial length also makes measurement timing relevant. (myopiainstitute.org)

An absolute treatment effect is the difference between groups’ changes over a specified interval. In Jeffrey J. Walline and colleagues’ 2020 BLINK trial, 294 children aged 7–11 years were randomized to three contact-lens designs and followed for three years. High-add multifocal lenses produced an adjusted refractive difference of 0.46 D compared with single-vision lenses, with a 95% confidence interval of 0.29–0.63 D, and 0.23 mm less axial elongation. The reported relative slowing was approximately 43% for refraction and 36% for axial growth. Percentage reduction divides the between-group difference by comparator progression: hypothetically, preventing 0.20 mm represents 50% slowing when controls elongate 0.40 mm, but 25% when they elongate 0.80 mm. Thus, percentages depend on the comparator’s growth rate as well as duration; an early percentage effect cannot simply be projected across subsequent years. (jamanetwork.com)

Follow-up duration determines whether a trial captures an initial response, sustained benefit, or loss of benefit after withdrawal. The 2019 IMI report recommended at least three years of study, including a treatment-free or control-treatment period to assess rebound. Its clinical summary specified at least one year of post-cessation observation. Rebound denotes accelerated growth after stopping treatment, rather than merely the resumption of progression. By contrast, the 2025 IMI review led by Mark A. Bullimore and Christine F. Wildsoet required at least 12 months of follow-up, concurrent controls, and axial-length measurements when selecting trials of established technologies: this inclusion threshold was not evidence of long-term durability. (myopiainstitute.org)

Adherence and attrition affect interpretation independently of the intervention’s optical or pharmacological mechanism. Lens-wearing hours, drop administration, missed visits, and reasons for discontinuation document actual exposure and retention. Intention-to-treat analysis retains participants in their assigned groups even after treatment changes, preserving the randomized comparison; analysis restricted to protocol-compliant completers can select a different population. BLINK retained 287 of 294 participants at its three-year visit. Safety assessment requires systematic adverse-event reporting and evaluation of visual function and ocular health, not only progression endpoints. (myopiainstitute.org)

Cross-trial results differ in participant age, baseline refraction, population composition, comparator, treatment exposure, measurement procedures, and follow-up. Consequently, a larger percentage reduction in one trial does not automatically establish superiority over an intervention tested elsewhere. The 2025 IMI review did not undertake meta-analysis because of heterogeneous study data; for selected similar interventions it presented medians and interquartile ranges instead. Direct randomized comparisons provide a stronger basis for comparative claims than rankings assembled from separate trials with different control-group progression and observation periods. (myopiainstitute.org)

Research gaps and emerging approaches

The unresolved biological problem is how visual experience produces sustained elongation in the human eye, rather than merely short-lived changes in focus or tissue thickness. The 2019 International Myopia Institute (IMI) experimental-model report, led by David Troilo and Earl Smith, described locally regulated retinal responses to defocus and signaling through the retinal pigment epithelium, choroid, and sclera. However, the complete sequence connecting image detection to altered scleral extracellular-matrix synthesis has not been established in humans. Candidate mediators include dopamine, retinoic acid, and nitric oxide; their identification in animal experiments does not establish their relative contributions to ordinary childhood myopia. Outstanding questions include how competing visual signals are integrated over time and retinal area, how light exposure interacts with circadian rhythms, and which molecular changes initiate growth rather than follow it. These distinctions matter for translating experimental targets into human treatments. (myopiainstitute.org)

Adult progression and the durability of childhood treatment effects remain separate evidence gaps. The 2023 IMI adult report documented continuing refractive progression and axial elongation in young adults, particularly in university populations, but emphasized the lack of large trials establishing treatment efficacy in adults. Slower average progression makes an intervention’s effect harder to distinguish from measurement variability, requiring longer observation or larger samples than many childhood studies. For childhood interventions, continued benefit during treatment does not establish how much benefit remains after withdrawal. Follow-up must distinguish ordinary age-dependent growth from rebound—accelerated progression after stopping treatment—and determine whether repeated treatment or delayed onset changes eventual adult refraction. Red-light research illustrates this issue: a two-year post-trial follow-up reported sustained effects with continued exposure but rebound after cessation. (myopiainstitute.org)

Repeated low-level red-light exposure is an emerging approach with efficacy findings that must be distinguished from retinal-safety evidence. In Yu Jiang and colleagues’ multicenter randomized controlled trial, published in 2022, 264 Chinese children aged 8–13 years were randomized; adjusted axial elongation over 12 months was 0.13 mm with red-light exposure and 0.38 mm with single-vision spectacles alone. (researchportalplus.anu.edu.au) Common research protocols use approximately 635–650 nm laser light for three minutes twice daily, but devices differ in power and retinal exposure. Proposed mechanisms involving mitochondrial activity, nitric oxide, or choroidal circulation remain incompletely established. The 2025 IMI intervention report documented safety concerns including reduced foveal cone density, a report of bilateral vision loss after five months of exposure, and measurements showing that some devices approached or exceeded exposure limits. These findings leave questions about cumulative dose, device-specific risk, and sensitive detection of retinal injury; absence of injury in a short trial does not establish long-term safety. (pmc.ncbi.nlm.nih.gov)

Prediction research requires broader population representation and validation outside the datasets used to construct a model. The 2025 IMI genetics report identified more than 1,000 common variants associated with refraction or myopia, while emphasizing incomplete functional validation and unexplained heritability. Genetic association is therefore not equivalent to a clinically reliable prediction of onset, progression, or complications. Genome-wide association studies and genetic risk models need evaluation across ancestries and environmental settings rather than assuming that performance transfers unchanged. (myopiainstitute.org) Biometric prediction has analogous requirements. The PreMO risk indicator combines age, spherical-equivalent refraction, axial length, and parental myopia; its 2024 cross-population validation used independent Hong Kong and ethnically diverse UK cohorts after development in white UK children. Such validation tests whether a model remains informative when background incidence and ocular-growth distributions differ. (pmc.ncbi.nlm.nih.gov)

Refractive change and axial elongation are useful trial outcomes, but their relationship to lifelong visual function remains an inferential bridge. Mark Bullimore and Noel Brennan’s 2019 analysis estimated that one diopter less myopia would correspond to approximately 40% lower likelihood of myopic maculopathy, using epidemiological relationships between refractive magnitude and disease. This was not a randomized demonstration that reducing childhood progression by one diopter prevents that proportion of later complications. Establishing the long-term link requires observation of treated cohorts into ages when maculopathy becomes common, with structural disease and visual impairment measured directly rather than inferred solely from refraction. (pubmed.ncbi.nlm.nih.gov)

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