Glaucoma

Glaucoma is a group of eye diseases in which progressive damage to the optic nerve, usually with loss of retinal ganglion cells, causes characteristic visual field loss and, if untreated, blindness. It is one of the leading causes of irreversible blindness worldwide. Because the optic nerve is part of the central nervous system, the damage cannot be reversed once it has occurred, which makes early detection and sustained treatment central to the field of medicine and public health. Elevated intraocular pressure is the best-known risk factor, but it is neither necessary nor sufficient for disease, and the condition is studied across ophthalmology, neuroscience, genetics and epidemiology.

This entry first defines glaucoma and explains the anatomy of the optic nerve head and the fluid dynamics of the eye that govern intraocular pressure. It then sets out the main classes of disease, primary open-angle, angle-closure, normal-tension, secondary and congenital glaucoma, together with their risk factors, genetic background and global burden. The later sections cover clinical symptoms, diagnostic tests, the cellular mechanisms of nerve damage that go beyond pressure, medical, laser and surgical treatment, long-term management, the historical development of the concept and its instruments, and the open research questions that remain.

Definition and clinical significance

Glaucoma is best understood as a family of progressive optic neuropathies rather than one disease. Authors describe it as a group of optic neuropathies in which retinal ganglion cells degenerate progressively, making it the leading cause of irreversible blindness in the developed world. Across its variants, the shared endpoint is the loss of retinal ganglion cells and their axons, which produces a recognisable pattern of optic nerve damage. That damage in turn produces peripheral visual field loss while central visual acuity is initially preserved. Because the diagnosis rests on structural and functional damage, optic nerve damage and visual field loss are required for a glaucoma diagnosis.

The damage is permanent because the lost neurons are not replaced. Glaucoma is challenging to treat because of the irreversible loss of retinal neurons. Current therapies are limited in what they can achieve: pharmaceutical and surgical treatments have mainly a slowing effect on disease progression. The disease is also frequently described as a "sneak thief" of sight, a nickname that reflects how little it announces itself. It is a silent, slowly progressive disease. Early stages are mostly asymptomatic and painless, so many patients do not notice loss until a substantial part of their field has already been affected, at which point many people with the disease do not realize they have it until it is too late for effective treatment.

The public health stakes follow from these features. Glaucoma is the leading cause of irreversible blindness globally, affecting more than 70 million people, and its prevalence is expected to rise with aging populations. Yet much of the harm is avoidable: most vision loss resulting from glaucoma can be prevented through early detection and treatment strategies. For this reason it is often described as one of the leading causes of irreversible but preventable blindness. The gap between these two facts is one of the central problems of epidemiological and clinical practice in the field.

A key conceptual distinction is between glaucoma as a diagnosis and raised intraocular pressure as a risk factor. Ocular hypertension describes pressure inside the eye above normal, without evidence of optic nerve damage or vision loss; it is not an eye disease itself but a risk factor for developing glaucoma. The ocular hypertension category is therefore defined by a measurement, whereas glaucoma is diagnosed when pressure, or other factors, begin to harm the optic nerve and affect vision. The separation matters in practice. Simply measuring pressure is not enough to diagnose glaucoma. In the Ocular Hypertension Treatment Study, untreated ocular hypertensive patients had a 9.5% risk of developing glaucoma at five years, compared with 4.4% among those who were treated. Conversely, some people develop optic nerve damage at pressures that are not elevated, which is why pressure alone cannot define the disease.

Anatomy of the optic nerve head and retina

Retinal ganglion cells and their axons

The retina sends its output to the brain through retinal ganglion cells (RGCs). Their cell bodies lie in the inner retina, and their long axons spread across the retinal surface, forming the retinal nerve fiber layer. These axons converge on the optic disc, where they leave the eye as the optic nerve. Because the optic nerve is an extension of the central nervous system, its fibers are unmyelinated inside the eye and only gain myelin behind the eyeball. The optic nerve head is often described in four zones: the surface nerve fiber layer, the prelaminar region, the laminar region and the retrolaminar region. The laminar region is the biomechanically critical one.

The lamina cribrosa

The lamina cribrosa is a perforated plate of connective tissue in the scleral canal, and its pores let bundles of RGC axons pass out of the eye. It is a porous collagen structure through which the axons of retinal ganglion cells pass on their path from the retina to the brain. The plate sits at a pressure boundary: the intraocular pressure in front of it is opposed by cerebrospinal fluid pressure behind it, so its load depends on the difference between the two. When intraocular pressure rises, the plate is pushed backward and bows. This displacement can kink and pinch axons inside the pores, which slows or blocks the flow of axoplasm along them. Histological studies of human glaucomatous eyes have reported compression and damage of axons at this level, and cell death follows when the axonal damage persists. Lamina thinning and posterior deformation are more pronounced in glaucomatous eyes than in normal eyes. Computational work points in a similar direction: one theoretical model estimated that laminar sheets could shift by about 18.6 μm at 40 mmHg, a displacement large enough to injure axons, and a two-scale analysis suggested that in-plane shear at the posterior insertion of the lamina may rise as pressure increases. Whether the dominant injury is mechanical or ischemic remains debated.

Cupping and the neuroretinal rim

Ophthalmologists assess the optic disc by the neuroretinal rim, the band of tissue between the disc margin and the central cup. In most healthy eyes this rim is widest inferiorly, then superiorly, nasally and thinnest temporally, a pattern known as the ISNT rule. As axons are lost, the rim narrows and the cup enlarges. In glaucomatous eyes, rim loss is predominantly identified in the inferior and superior disc regions, thus, cupping is prone to vertical expansion. Because loss follows the fiber bundles, focal or diffuse rim loss is associated with the distribution of nerve fibers and the impaired area. Localized notching or wedge-shaped defects in the nerve fiber layer therefore map onto specific visual field regions. Cupping alone is not diagnostic. Many healthy people naturally have large optic nerve cups, while some patients with glaucoma have relatively small cups. Large healthy discs often have larger laminae, and violation of the ISNT rule also occurs in large optic disc cups of nonglaucomatous origin, with a greater frequency in the pediatric population.

Blood supply and vulnerability

The laminar region receives its blood mainly from the short posterior ciliary arteries, which form the circle of Zinn-Haller around the optic nerve. This arrangement is an end-arterial system with little collateral redundancy, so the lamina is particularly sensitive to drops in perfusion pressure. Ocular perfusion pressure depends on both blood pressure and intraocular pressure, and a postmortem study of human optic nerve heads found that the blood supply to the ONH is less robust in glaucomatous individuals. That study suggested that sparse vascularity could raise the risk of glaucoma when combined with other factors, and it noted that elevated pressure lowers perfusion and that deformation of the lamina could pinch off capillaries. The vascular hypothesis holds that insufficient perfusion leaves the optic nerve vulnerable, even when IOP is in the "normal" range. Blood flow measurements add nuance: flow is reduced in advanced disease, while some primate experiments suggested an early increase in flow before damage advances, a pattern that has not been fully confirmed in humans.

Aqueous humor dynamics and intraocular pressure

Production and the production–drainage balance

The anterior segment of the eye contains aqueous humor, a clear fluid made continuously by the ciliary body, a ring of tissue behind the iris. The ciliary processes produce it through a mix of active secretion and ultrafiltration from the blood. The fluid flows from the posterior chamber through the pupil into the anterior chamber, and the eye's roughly fixed volume means that intraocular pressure (IOP) depends on a continuous balance between production and drainage. Because the balance is so precise, small shifts in either direction raise or lower pressure noticeably. Several glaucoma drugs work on this side of the equation: some reduce secretion by inhibiting enzymes such as carbonic anhydrase, which helps drive ion transport in the ciliary epithelium.

Conventional outflow

The main drainage route is the conventional pathway. Fluid crosses the trabecular meshwork, a porous tissue of cells embedded in an extracellular matrix rich in collagen at the iridocorneal angle, and then enters Schlemm's canal, a circular channel at the limbus lined by a thin endothelium. From there, fluid passes through collector channels into the episcleral venous system. The meshwork has uveal, corneoscleral and juxtacanalicular regions, and the juxtacanalicular tissue next to Schlemm's canal provides most of the resistance. Estimates vary, but the trabecular route is generally described as handling the large majority of drainage in the healthy eye. Its function is often expressed as outflow facility, the volume drained per minute for each millimetre of mercury of pressure, in µL/min/mmHg. Meshwork cells can contract and change shape, which alters the spacing between tissue elements and therefore the flow resistance; the endothelial lining of Schlemm's canal forms the final barrier before fluid leaves the eye.

Uveoscleral outflow

The second route is the unconventional or uveoscleral pathway. Fluid moves through spaces between the fibres of the ciliary muscle and then out through the surrounding tissues rather than through the meshwork. In the healthy human eye this pathway is minor, accounting for roughly a fifth of total outflow. Because the ciliary muscle changes its tone, it can redistribute flow between the two routes: when the muscle relaxes, the trabecular spaces narrow and trabecular outflow falls, while uveoscleral outflow rises. This shared control is one reason the two pathways are studied together, and it is also why drugs acting on the ciliary muscle can change pressure through either route.

Normal range and diurnal variation

Normal IOP is commonly given as about 10 to 21 mmHg, with a population mean near 15 to 16 mmHg. The upper figure of 21 mmHg is a convention used for screening and diagnosis rather than a biological boundary. Pressure also varies over the day, usually by several mmHg, and in many people it peaks in the early morning. Posture and sleep alter it further, and lying flat generally raises pressure. Because of this variation, a single clinic reading captures only one moment and can understate or overstate a patient's typical pressure. Clinicians therefore rely on repeated measurements, and in some cases on home or 24-hour monitoring. Corneal thickness and tonometer technique also influence the reading, so the number must be interpreted with these factors in mind.

Resistance and pressure transmission to the optic nerve

IOP can be approximated by a simple relation: pressure roughly equals episcleral venous pressure plus the product of the production rate and the reciprocal of outflow facility, $$IOP \approx P_{ev} + \frac{F}{C}$$ where $F$ is the aqueous production rate and $C$ is outflow facility. Raised resistance in the meshwork lowers $C$, so pressure rises even when production is unchanged. The pressure acts on the whole globe, but the optic nerve head is the region where it matters most for glaucoma. The relevant force there is the pressure difference across the lamina cribrosa: the sclera-bound fenestrated plate through which retinal ganglion axons leave the eye. This translaminar gradient depends on IOP in relation to the pressure in the tissue behind the eye, so the effective load on the optic nerve head is not identical to the pressure measured by tonometry. A sustained gradient deforms the lamina cribrosa and compresses the axons passing through it, which is the starting point of the mechanical pathway described in later sections.

Classification of glaucoma

Glaucoma is classified along several overlapping axes. The most widely used distinctions concern whether a specific cause can be identified, how the anterior chamber angle is configured, and the age at which the disease appears. Each axis informs a different part of management, but none fully captures the underlying biology, so a single patient may fit more than one label.

Primary and secondary glaucoma

Primary glaucoma is diagnosed when no clear cause can be identified beyond the disease process itself. Secondary glaucoma arises from an identifiable condition that raises intraocular pressure or damages the outflow pathway or optic nerve. The most common secondary causes include pseudoexfoliation syndrome, in which flaky extracellular material accumulates on the lens, iris and trabecular meshwork and is among the leading identifiable causes worldwide; pigment dispersion, in which pigment shed from the iris clogs outflow and typically affects young, myopic adults; uveitis; trauma, including angle recession after a blow to the eye; prolonged corticosteroid use; and neovascular glaucoma, in which new vessels grow across the angle, usually in association with diabetic or ischemic retinal disease. The guiding principle in secondary disease is to treat the underlying cause first, for example by controlling inflammation or withdrawing a steroid, although pressure-lowering treatment is often still required.

Open-angle and angle-closure glaucoma

The angle is the junction between the iris and the cornea through which aqueous humor leaves the eye. Its configuration is assessed by gonioscopy, in which a special contact lens allows the examiner to view the trabecular meshwork and the surrounding structures. The Shaffer grading system ranks the angle from grade 0, fully closed, to grade 4, the widest, which corresponds to an opening of roughly 45 degrees. In open-angle glaucoma the angle looks open, and the obstruction lies within the meshwork or in the tissues downstream of it. In angle-closure glaucoma, the peripheral iris lies against or blocks the trabecular meshwork, so that outflow is mechanically impeded. This distinction matters clinically: eye drops alone do not reopen a mechanically closed angle, whereas laser peripheral iridotomy, which creates a small channel through the iris, is the usual first-line step in primary angle closure.

Age-based classes

Adult glaucoma refers to disease that appears in adulthood, usually after the mid-30s to 40s, and is the form that predominates in most population studies. Juvenile open-angle glaucoma describes an open-angle disease without a secondary cause that begins in childhood or early adulthood, commonly defined as onset between about 3 and 35 years, although age limits differ between classification systems. Congenital or infantile glaucoma, often termed primary congenital glaucoma, presents from birth up to about age 3. It results from developmental abnormalities of the trabecular meshwork and angle structures, and it is often bilateral. Congenital forms can also occur alongside other developmental eye anomalies, which are grouped as secondary or syndromic congenital disease. The exact age boundaries used for infantile and juvenile categories vary between sources.

Limits of classification

The categories are not mutually exclusive. Pseudoexfoliation may coexist with a primary open-angle pattern, and chronic angle closure can leave peripheral anterior synechiae, which are adhesions between iris and angle, so that the angle later behaves as though it were open. Terms such as normal-tension glaucoma and ocular hypertension are defined by pressure level rather than by mechanism, so they cut across the mechanistic categories. Angle configuration can also change with pupil size, lens growth and time, and gonioscopic interpretation depends on examiner skill. For these reasons, classification is best understood as a practical framework rather than a complete taxonomy. Its main clinical value lies in guiding the choice of laser procedures, eye drops and surgery: angle closure is typically treated first by opening the iris, open-angle disease by lowering pressure through drops, laser or incisional surgery, secondary disease by addressing the cause, and congenital disease usually by surgery on the drainage structures.

Primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is the most frequent subtype of the disease. In the United States and western Europe, open-angle forms account for most cases, and POAG is the dominant type within that group. Reported shares vary by population and source. One patient-education site attributes 90 percent of glaucoma cases to POAG, while a clinical-trial registry summary gives a range of 60 to 70 percent. POAG is also the commonest glaucoma in populations of European origin, and it is the leading cause of irreversible blindness among African Americans in the United States.

The course is slow and usually silent. Optic nerve damage advances without pain, and people can lose a large part of their visual field before they notice anything. Early loss begins in the peripheral field, and a healthy fellow eye can mask it, so the disease often remains hidden until it reaches an advanced stage. Involvement is typically bilateral, but the two eyes frequently differ in severity, and one eye may show marked damage while the other shows little or none. Because the disease is so often asymptomatic, a routine eye examination is the usual route to diagnosis.

Diagnosis rests on several findings rather than a single test. Gonioscopy shows an open anterior chamber angle, and the optic disc shows progressive thinning of the neuroretinal rim and loss of the retinal nerve fiber layer. A common threshold for abnormal cupping is a cup-to-disc ratio above 0.5, and a difference of 0.2 or more between the two eyes is also considered suspicious. The visual field defects that accompany these changes typically follow the nerve fiber bundles, including arcuate scotomas and nasal steps, and they reflect the loss of retinal ganglion cells and their axons. Some definitions include a requirement that intraocular pressure has exceeded 21 mmHg at some point, whereas other sources state that a raised pressure reading is not essential for diagnosis, which reflects the disagreement about how central pressure is to the definition.

Intraocular pressure is the best-established modifiable risk factor. Normal values are generally taken as 10 to 21 mmHg, and the upper limit of 21 mmHg is a statistical convention, not a biological boundary. Pressures above this level increase the risk of visual field loss, and the risk rises further at higher levels, particularly above 26 to 30 mmHg. Fluctuations in pressure also appear to accelerate progression. Clinical trials have shown that lowering pressure slows progression, but the benefit at lower pressures remains uncertain. In the Ocular Hypertension Treatment Study, patients with pressures between 24 and 32 mmHg who received treatment had a lower five-year incidence of very early glaucoma (4.4 percent) than untreated patients (9.5 percent). The evidence for patients with pressures between 21 and 24 mmHg is less clear.

Pressure is not the whole story. Many people with high readings never develop glaucoma, and some people with normal readings do. Progression in patients whose pressure stays within the normal range is discussed further under normal-tension glaucoma and related mechanisms, and it is one reason why pressure alone is an incomplete screening tool.

Primary angle-closure glaucoma

Anatomical basis

Primary angle-closure glaucoma (PACG) begins with a structural problem in the front of the eye. The angle, the junction where the iris meets the cornea and the trabecular meshwork lies beneath, can become too narrow for aqueous humor to leave the eye. Eyes that are prone to this usually have a shallow anterior chamber, a lens that is thick or sits further forward, and crowding of the tissues around the angle. A short axial length (the front-to-back dimension of the eyeball) and a small cornea are also common in affected eyes. Hyperopia is the refractive error most often linked to this anatomy because a shorter eye tends to have a shallower chamber.

The usual mechanism is pupillary block. Aqueous humor made behind the iris must pass through the pupil to reach the front chamber. When the iris lies against the lens, that flow is restricted, and pressure builds behind the iris. The iris then bows forward and can press against the trabecular meshwork, blocking drainage. The narrowing can become self-reinforcing, and in some eyes it leads to peripheral anterior synechiae, which are permanent adhesions that keep the angle closed even after the pressure falls. Age matters here: the lens grows thicker over the decades, which crowds the angle further, and most cases occur after 40. Why some eyes with narrow angles develop closure and others do not is still incompletely understood, and it is also difficult to predict which narrow-angle eyes will eventually have an acute attack.

Acute attacks

An acute attack happens when the angle closes suddenly and completely. Intraocular pressure can rise very quickly, and the patient typically experiences severe eye pain, redness, blurred vision, headache, seeing halos or coloured rings around lights, and nausea or vomiting. On examination the cornea may look hazy from pressure-induced edema, the pupil is often mid-dilated and does not respond normally to light, and the front chamber is shallow. Because the optic nerve can be damaged within hours, the condition is treated as an ophthalmic emergency. Lowering pressure with drops and, once the eye is stable, creating an opening in the iris with laser peripheral iridotomy are the standard steps, and this treatment is also used prophylactically in eyes with narrow angles.

Chronic and intermittent closure

Not every case announces itself with a crisis. In chronic angle closure, gradual or repeated partial contact between iris and meshwork causes progressive peripheral anterior synechiae, and pressure may rise slowly or fluctuate. Intermittent closure can cause brief episodes of blurred vision or haloes that resolve spontaneously, so patients may not seek care. Because the angle narrows before any visual field defect appears, some people reach a stage of optic nerve damage without having recognised earlier symptoms. Studies in East Asia have reported that primary angle closure in that region is often asymptomatic, which makes examination of the anterior chamber angle important for at-risk individuals.

Geographic and demographic pattern

PACG is far more common in Asia than elsewhere. A meta-analysis of population-based studies estimated a pooled prevalence of about 0.75% among adult Asians, with prevalence rising steeply with age, and reported a female-to-male ratio of about 1.5 to 1. Chinese populations showed the highest estimates among the ethnic groups studied. An estimate for people over 40 worldwide puts the total near 17 million, with about 12 million in Asia. Acute attacks follow a similar gradient: incidence among East and South Asians has been reported as several times higher than among Europeans. Anatomical differences, including shorter axial lengths and shallower chambers, are the main explanations offered, although researchers still debate how far pupillary block alone accounts for the pattern. Within acute attacks, women are more often affected, and the peak occurs in people in their sixties.

Normal-tension glaucoma

Normal-tension glaucoma (NTG), also called low-tension or normotensive glaucoma, is a form of open-angle glaucoma in which the optic nerve and visual field deteriorate while intraocular pressure stays within the statistically normal range. Reference values usually place the upper limit at about 21 mmHg, so people with NTG have readings below the level used to define ocular hypertension. Structural and functional damage resembles that of primary open-angle glaucoma, which is why NTG is generally classed as a subtype of it rather than as a separate disease.

Its share of cases varies sharply by population. In the Tajimi study in Japan, NTG accounted for about 92% of open-angle glaucoma, and in the Singapore Malay Eye Study the figure was about 85%. Chinese cohorts report proportions ranging from roughly half to more than four-fifths, while studies in European-ancestry populations generally find a smaller share. A Japanese nationwide survey found that about 78% of people with open-angle glaucoma had pressures below 21 mmHg, and that normal-pressure disease was roughly 3.5 times as common as high-pressure disease in that population. Researchers have linked this pattern partly to the apparent absence of an age-related rise in intraocular pressure among Japanese adults, which would lower the prevalence of ocular hypertension and therefore raise the relative share of NTG. The epidemiological picture is therefore shaped by both genetic background and measurement practice.

Several mechanisms have been proposed, and most investigators regard them as overlapping rather than mutually exclusive. The mechanical hypothesis holds that some optic nerves are unusually sensitive to normal pressure, so that the pressure difference across the lamina cribrosa, the translaminar gradient, damages axons even at low pressures. The vascular hypothesis focuses on vascular dysregulation, the failure of a tissue to keep its blood supply steady when perfusion pressure changes. Ocular perfusion pressure is commonly estimated as two-thirds of mean arterial pressure minus intraocular pressure, and nocturnal blood pressure dips, low systolic pressure and low ocular perfusion pressure have all been associated with faster visual field loss. Patients with primary vascular dysregulation often report cold extremities, migraine or Raynaud-type symptoms, and such features are more common in NTG than in high-pressure disease. Endothelial dysfunction, reduced nitric oxide availability and raised endothelin-1 have been reported in some of these patients. Beyond the vascular and mechanical pathways, cerebrospinal fluid pressure within the optic nerve sheath and oxidative stress, glutamate toxicity and mitochondrial dysfunction have been suggested as contributors to ganglion cell death. Genetic evidence is also growing: a family history of glaucoma is reported in as many as about one in five patients, mutations in the OPTN and TBK1 genes have been identified in some NTG families, and a genome-wide association study in Japanese patients linked a variant near CDKN2B on chromosome 9p21 to the condition.

Clinically, NTG shares many features with primary open-angle glaucoma, so the two are difficult to separate on examination alone. Differences tend to emerge in the frequency of optic disc haemorrhages, in the association with systemic vascular traits and in the pattern of progression. Confirming NTG is also a matter of exclusion: clinicians must rule out other causes of optic neuropathy, such as compressive lesions and inflammatory disease, and must recognise that a few clinic readings cannot capture the peaks and fluctuations that may matter. The evidence is not uniform. One study found no difference in ocular perfusion pressure or ophthalmic artery flow between NTG patients and controls, suggesting that vascular insufficiency alone may not account for the disease. Trial data also show that pressure lowering helps but does not stop progression in every patient. In the Collaborative Normal-Tension Glaucoma Study, treatment slowed progression, yet the authors suggested that a 30% reduction from baseline may be insufficient for some patients or that factors other than pressure play a role. In an untreated Japanese cohort with a mean baseline pressure of 12.3 mmHg, the estimated probability of progression at five years was 66%.

These findings bear directly on diagnosis. Because pressure-based screening misses most people with NTG, a 21 mmHg cutoff would fail to detect the majority of cases in populations like Japan's. Detection therefore depends on examining the optic disc, measuring visual fields and imaging the nerve and retinal nerve fibre layer, supplemented by attention to vascular history and blood pressure patterns. Reliable biomarkers that identify NTG early remain unavailable, which is one reason the diagnosis is often delayed. The long-term consequences are substantial: in one long-term Japanese study, the 20-year incidence of blindness was about 9.9% in one eye and 1.5% in both eyes among patients with NTG.

Secondary and congenital glaucoma

Secondary glaucoma

Secondary glaucoma covers cases in which an identifiable process, rather than an idiopathic one, drives pressure up and injures the optic nerve. Common etiologies include pseudoexfoliation and pigment dispersion syndromes, intraocular infection or inflammation, retinal vascular disease, blunt trauma, eye surgery, neovascularization, uveitis, lens-related problems, and corticosteroid use. In one 2021 cross-sectional study of 106 patients over 40, lens-induced glaucoma was the most common cause (44.34%), followed by uveitic (20.8%), traumatic (17.9%), neovascular (10.4%), and pseudoexfoliative (2.8%) cases, so the relative frequency of causes varies considerably by population and clinical setting.

Two of the best-known mechanisms involve material that physically blocks the trabecular meshwork. In pseudoexfoliation, flaky deposits shed from the lens capsule accumulate in the drainage angle, and these flakes are shed by the continuous movement of the iris as the pupil changes size. The condition is considered the most common cause of secondary open-angle glaucoma, and it is more severe than primary open-angle glaucoma. In pigment dispersion syndrome, granules rubbed off the back of the iris lodge in the meshwork, and the condition is commoner in young, myopic (shortsighted) men.

Inflammation and medication form another group. In uveitis, about 2 in 10 people with uveitis develop uveitic glaucoma. The pressure rise reflects both direct inflammatory damage to the outflow tissues and the corticosteroids used to treat the inflammation, which lower aqueous outflow. Steroid-induced elevation is a separate pathway: prolonged use of steroids in drops, tablets, sprays, or creams can alter the meshwork's microstructure, and this form of secondary glaucoma is often reversible if the steroid is discontinued or replaced under medical supervision. Neovascular glaucoma, in which new vessels grow across the angle, is a serious angle-closure variant.

Management follows the principle of treating the cause first. Most secondary glaucomas will require treatment of the underlying cause, drops to lower the pressure (and possibly tablets in the short-term) and anti-inflammatory drops if there is an inflammatory component. Where the trigger is removed, pressure may normalize, but where optic nerve damage has already occurred, pressure-lowering surgery or long-term medication may still be needed.

Congenital glaucoma

Primary congenital glaucoma results from developmental defect(s) of the trabecular meshwork and anterior chamber angle that prevent adequate drainage of aqueous humor, resulting in elevated intraocular pressure (IOP) and stretching of the sclera that produces an enlarged globe (buphthalmos). It has a prevalence of one in 10,000–68,000 people in Western countries, and it is responsible for 5–18% of all childhood blindness cases.

Presentation is often subtle. The classic symptoms are epiphora, blepharospasm and photophobia, but these symptoms are often missed, and excessive tearing may be mistaken for a blocked tear duct. Parents or clinicians more often notice that the patient usually presents because of corneal clouding and ocular enlargement. Corneal edema results from the high pressure, and the eye's elastic tissues stretch: the increased corneal diameter may lead to tears in the relatively inelastic Descemet membrane, known as Haab striae. Most commonly, infants present at less than 6 months of age. Examination of the optic nerve may show a cup-to-disc ratio greater than 0.3 in infants with glaucoma, and asymmetry between the two eyes is also suggestive.

Surgery is the definitive treatment, and medication is only a temporizing step. Goniotomy and trabeculotomy are standard first-line treatments for PCG due to their effectiveness in this patient population and their favorable safety profile. When the cornea is hazy, trabeculectomy ab externo is the initial procedure of choice. For refractory cases, trabeculectomy and glaucoma drainage devices serve as second-line therapies, and advanced cases may require cyclodestructive procedures reserved for eyes with limited visual potential. Because infant tissue is more pliable, cupping may occur rapidly in infants, but it is reversible with surgical management and IOP control. Early recognition therefore matters: untreated disease leads to blindness, whereas timely surgery and follow-up for refractive errors and amblyopia give the best chance of preserving vision.

Risk factors and genetic background

Glaucoma has no single cause, so its risk profile combines demographic, ocular, systemic and inherited factors. The evidence for each is uneven. A 2024 meta-analysis of prospective studies rated the association with primary open-angle glaucoma (POAG) as strong for intraocular pressure and family history, but only weak for age and myopia, and suggestive for sex. Two factors showed strong evidence (IOP, family history of glaucoma); one showed suggestive evidence (female), and three showed weak evidence (age, IOP treatment, myopia). Pressure is discussed in its own section; the remaining factors are summarized here.

Ancestry is one of the clearest demographic risks. Analyses of the Ocular Hypertension Treatment Study (OHTS) and the European Glaucoma Prevention Study (EGPS) identified age as a predictor of progression from ocular hypertension to POAG In both the OHTS and EGPS, age was also found to be an important risk factor for the conversion of OHT to POAG. Reviews of population data report that primary open-angle glaucoma was found to be four to six times more frequent among individuals of African-American origin compared to Caucasian. In Black patients, the disease also tends to advance differently: its onset is earlier and disease progression is faster and more refractory to treatment.

Several ocular features are also linked to risk. Multiple studies connect myopia with a higher likelihood of POAG In several studies, myopia was shown to be a risk factor for POAG. Corneal thickness is a more unusual finding. In OHTS, the risk of developing glaucoma was highest among participants with the thinnest central corneal measurements within all IOP groups. Part of this association may be artefactual, because IOP tends to be read lower in patients with thinner corneas. A second explanation proposes that thin corneas reflect less-rigid support structures around the optic nerve head and a resultant increased propensity for damage. Vascular and systemic factors are less settled. A review focused on people of African descent classed vascular abnormalities, and positive family history among the factors definitively associated with POAG risk. Diabetes and hypertension also appear among the systemic comorbidities examined in case-control work, though their contribution is less clearly defined.

Family history has a real but incomplete weight. In the Barbados Family Study, family history to be a major risk factor for glaucoma confirmed by direct examination of the relatives. Even so, family history alone cannot account for the observed prevalence, which points to a polygenic background rather than a single inherited cause.

Monogenic forms are the minority. About 5% of primary open angle glaucoma (POAG) is currently attributed to single-gene or Mendelian forms of glaucoma (ie glaucoma caused by mutations in myocilin or optineurin). The myocilin gene (MYOC) is the most important of these, although estimates of its share vary between series, from approximately 2.2% of cases to 2% to 4% of patients with POAG. The protein is normally produced in the trabecular meshwork, and disease-associated myocilin mutations cause protein misfolding, intracellular protein aggregation in the endoplasmic reticulum (ER), and lack of secretion into the extracellular matrix. MYOC variants are often inherited as a dominant trait, and myocilin mutations are also co-inherited with POAG in an autosomal dominant pattern and have been detected in cohorts of POAG patients from around the world. The juvenile-onset form, an early onset (<40 years) sub-set of POAG, is also linked to MYOC. Other single-gene forms involve different pathways, such as LTBP2, which causes autosomal recessive PCG.

The extracellular matrix of the trabecular meshwork is a recurring theme in the genetics. Matrix metalloproteinases and their tissue inhibitors continually reshape the matrix, and this remodeling influences outflow resistance which is continuously remodelled by various matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs). Angle-closure genetics shows a similar pattern. Collagen-related genes have been prominent: Eight loci were identified in one or both of two recent large genome-wide association (GWA) studies on PACG patients, and COL11A1 that encodes one of the alpha chains of type XI collagen was one of the genes identified in both of the studies. Many candidate-gene findings in this area remain unconfirmed; these findings are not generally considered definitive, and putative roles of genes suggested by some studies were not confirmed in independent studies.

Genome-wide association studies (GWAS) have widened the picture considerably. Loci near Caveolin 1 and 2 (CAV1/CAV2), Transmembrane and coiled-coil domain-containing protein 1 (TMCO1), cyclin-dependent kinase inhibitor 2B antisense RNA 1 (CDKN2B-AS1) are among the many POAG associations identified. An African-focused study was described as the first GWAS of POAG comprising continental Africans, which verified the European glaucoma gene TXNRD2 and identified a novel candidate locus encompassing EXOC4 that requires further follow up in large African studies. A common variant near GLIS1 showed a significant association between GLIS1 variant rs941125 and glaucoma in humans, and this association was later confirmed and replicated in additional cohorts at a genome-wide level of significance. Epigenetic work adds another layer: a Mendelian randomization analysis utilizing a large-scale Genome-Wide Association Study for POAG identified 27 novel DNA methylation sites across 15 genes.

Genetic prediction remains limited. Most identified variants have small individual effects, and the Mendelian forms explain only a small fraction of cases. Each newly identified locus therefore adds modest predictive power, and common variants alone cannot yet reliably tell an individual's risk. Ancestry-matched cohorts are also needed, because many associations were first established in European populations.

Epidemiology and global burden

The most cited global estimate comes from a 2014 systematic review and meta-analysis of population-based studies of people aged 40 to 80. It put the pooled prevalence at 3.54%, with a prevalence of 3.05% for primary open-angle glaucoma and 0.50% for primary angle-closure glaucoma. The same model projected the number of affected people to rise from 64.3 million, to 76.0 million in 2020 and 111.8 million in 2040. Its projections multiplied age- and region-specific prevalence by population forecasts from the United Nations (see method, 2-9). Later reviews give somewhat higher present-day figures: a 2023 Lancet seminar cites nearly 95 million people with glaucoma, about 10 million of whom are blind in at least one eye. Differences between such figures mainly reflect the study years, age ranges and diagnostic criteria used.

Undetected disease is arguably the largest gap in the global picture. Because the disease is usually asymptomatic until late, more than 90% of cases are undiagnosed in low- and middle-income countries, whereas about half are undiagnosed in high-income countries. Late diagnosis has direct consequences: in low- and middle-income settings, as many as 35% of people diagnosed with glaucoma already have severe sight loss. A meta-analysis of 55 population-based studies published between 1990 and 2020 found that in every region of the world, at least half of all POAG cases were undetected. The undetected share was highest in Africa, at 94%, and lowest in Oceania, at 59%. By development level, the proportion of previously undetected cases was above 90% in countries with a low HDI, and that proportion fell to the 70% range in countries with medium to very high socioeconomic development. The same analysis estimated 43 million cases of undetected POAG in 2020, a number projected to rise to 67 million by 2040.

Prevalence also varies by region and by subtype. Open-angle disease is most common in Africa, where the pooled POAG prevalence was 4.20%, while angle-closure disease is concentrated in Asia. Among adult Asians, the pooled PACG prevalence was 0.75%, and over 80% of PACG worldwide occurs in Asia. Within Asia the pattern is not uniform: the prevalence of PACG was higher in East Asia than in South East Asia, while the burden of POAG was projected to be the highest in South-Central Asia by 2040. Future growth is expected to be uneven as well. Much of the increase in the number of glaucoma cases is attributable to significant increases in Asia and Africa. Among undetected POAG cases, Africa shows the largest projected relative increase, 86.3%, while Asia will hold a larger absolute share because of its population size.

The economic and social costs fall heavily on the people least able to absorb them. Glaucoma causes substantial functional impairment, diminished quality of life, and long-term economic burden for affected individuals and their families. The burden is concentrated in low- and middle-income countries, particularly sub-Saharan Africa, where structural health system barriers delay presentation until irreversible vision loss has set in. Within these settings, risk is also socially patterned. A study in rural Nigeria linked transportation limitations and female sex to a greater clinical and functional burden, and another Nigerian study found that socioeconomic deprivation increased the odds of blindness in glaucoma by about 4 times. Because most patients keep useful vision for much of their lives when treated, treatment is effective at slowing the rate of vision loss, which makes timely detection the central public-health lever.

Symptoms and clinical course

An asymptomatic early stage

Open-angle glaucoma usually causes no symptoms in its early years. The asymptomatic nature of glaucoma, particularly in early disease, means that substantial vision loss in one eye does not always translate into a perceptible loss of visual function. The main reason is binocular compensation: the healthier eye and the brain work together to mask a deficit in the other eye. In one study of patients with diagnosed disease, twenty-six percent of the patients, typically those with better mean deviation values, reported no visual symptoms. Patients who did report early complaints most often described needing more light, blurry vision and seeing glare rather than a defined gap in the field. Because of this, late presentation is common. People with high pressure but no symptoms, no family history, and no regular eye examinations are among those most likely to arrive with advanced disease.

How the visual field is lost

Field loss follows the anatomy of the retinal nerve fibers. Glaucoma usually leads to (arcuate) visual field defects that follow the course of the affected retinal nerve fibers. Clinical sources place the earliest changes mainly in Bjerrum's area, 10°-20° from fixation, whereas patient-oriented guides more often describe peripheral or side vision as the first to narrow. Both descriptions reflect the same process, which is that the paracentral and mid-peripheral field is affected before the far periphery. As the defects deepen, a nasal step may appear, a sudden horizontal cut-off on the nasal side. Eventually the remaining field becomes a small island, which patients describe as tunnel vision. The central visual field and the visual acuity are usually spared even up to end-stage glaucoma. When the defects in the two eyes coincide, the result is binocular field loss, which can impair reading, walking, and driving.

Acute angle-closure attacks

Acute angle closure is a separate and dramatic presentation. Its symptoms include severe ocular pain and redness, decreased vision, colored halos around lights, headache, nausea, and vomiting. Examination typically reveals conjunctival hyperemia, a hazy cornea, a fixed mid-dilated pupil, and anterior chamber inflammation. The gastrointestinal and neurological features can lead to misdiagnosis as a stomach illness or a neurologic disorder, which delays the correct treatment. Acute attacks are the exception rather than the norm: angle closure is usually chronic and progressive, but uncommonly it manifests as an acute attack of complete closure with severe symptoms. Many patients with chronic angle closure are asymptomatic. Some have only intermittent blurring or haloes without pain. Definitive surgical treatment after an attack is generally planned within 24 to 48 hours. This timing contrasts with chronic open-angle disease, which is usually silent and is managed on a longer schedule.

Factors that accelerate progression

Mean intraocular pressure is the only well-established, modifiable risk factor for glaucomatous progression, and multiple randomized clinical trials have demonstrated that lowering IOP slows visual field deterioration. Pressure fluctuation and low ocular perfusion pressure have been associated with progression, but the evidence is less robust. In a cohort of advanced primary open-angle glaucoma, long-term IOP fluctuations and disc hemorrhage were each independent predictors of field progression. The two factors were additive, and Long-term IOP fluctuations and disc hemorrhage are independent and additive risk factors of visual field progression in advanced glaucoma even at low IOPs. Disc hemorrhage was also much more frequent among progressing eyes, appearing in 40.5% vs. 17.4% of patients. The role of fluctuation is contested in normal-tension disease, where the role of short- and long-term IOP fluctuation in NTG progression is controversial. Adherence is a further determinant. Nonadherence to therapeutics increases the risk of disease progression, presumably because of mean IOP elevation. Simplified regimens, fixed-dose combinations, and automated reminders may help patients stay on treatment.

Diagnosis and screening

Glaucoma has no single definitive test. Clinicians typically combine several findings, because currently, there is no single accurate test to certify glaucoma, and the diagnostic procedure includes several time-consuming tests. The central logic is that a diagnosis rests on two kinds of evidence: functional loss in the visual field and structural damage to the optic nerve. In a case of definite disease, optic disc changes are normally visible, and it is very unusual that glaucoma would be diagnosed from visual field or OCT changes without disc features. Guidance from the UK National Institute for Health and Care Excellence (NICE) distinguishes patients with definite (or unequivocal) glaucoma, who have definite signs of glaucomatous optic neuropathy and are at imminent risk of visual loss, from patients with suspected (or equivocal) glaucoma, who have possible signs.

Tonometry and the limits of pressure

Intraocular pressure (IOP) is measured with tonometry. For decades, the gold standard for intraocular pressure measurement has been the Goldmann applanation tonometer. The instrument works on the Imbert–Fick principle, in which pressure inside of the eye is proportional to the force required for indentation. Its scale, however, assumes a fixed corneal thickness, and corneal properties introduce error: thin corneas result in a falsely low IOP, and thick corneas result in a falsely high IOP. Ocular hypertensive subjects have been found to have thicker corneas than people with glaucoma (592 ± 39 µm versus 536 ± 34 µm in one study), which suggests that corneal pachymetry should be performed to rule out an abnormally thick cornea as a reason for falsely high measurements of intraocular pressure. Central corneal thickness (CCT) is typically measured with an ultrasonic or optical pachymeter. Its role in screening remains debated: the American Academy of Ophthalmology noted that the evidence supporting the necessity of measuring CCT as part of screening for POAG or as a risk factor for glaucoma progression is not as strong, although CCT can still affect applanation readings in every patient.

Because pressure alone does not establish the diagnosis, a single normal result does not rule it out either. NICE guidance states that a decision to refer should not be based solely on IOP measurement using non-contact tonometry. Its referral criteria include optic nerve head damage on slit-lamp examination, a visual field defect consistent with glaucoma, or an applanation pressure of 24 mmHg or more.

Angle assessment and optic nerve examination

Gonioscopy, performed with a special contact lens, visualizes the structures of the drainage angle including the trabecular meshwork. If the trabecular meshwork can be seen the drainage angle is said to be open; if the drainage angle is obstructed and the meshwork cannot be visualized, the angle is said to be closed. Gonioscopy remains the reference method: one study noted that gonioscopy remains the gold standard for detecting and managing narrow angles. Anterior segment optical coherence tomography (AS-OCT) is used as a faster complement, particularly in busy clinics where narrow angles can be missed.

The slit-lamp examination of the anterior segment helps identify secondary forms, such as pseudoexfoliation, uveitic or pigmentary glaucoma. The optic nerve head is then examined binocularly with a slit lamp and a high-powered lens, usually after dilation to rule out other retinal diseases and to make it easier to examine the optic nerve.

Visual fields and imaging

Visual field testing is typically performed with static, automated perimetry, commonly performed using a Humphrey visual field machine. Functional loss is detectable only late: visual field defects begin to be obvious after a loss of about 40 per cent of retinal ganglion cells. Structural imaging can therefore detect damage earlier. The most popular technique is optical coherence tomography (OCT), a non-invasive test that provides images of the disc, the retinal nerve fibre layer and the ganglion cell count of the macula. Thinning of these layers can precede field loss, and optic nerve thinning on OCT may prompt treatment even when pressure appears normal.

Risk-based screening and automated detection

Screening strategies rely on risk stratification, because pressure, angle and disc findings do not carry equal weight for every patient. Large population screening has been limited by cost and by the need for specialist review, and automated methods are being explored as a way to widen access. Machine learning and deep learning systems have been trained on fundus photographs and OCT scans. One early study developed an algorithm using a large database of 494,661 teleretinal photographs acquired in diabetics, while another team labeled 48,116 color fundus images as "referable" (yes vs. no) for glaucoma based on human graders. Reported performance varies with dataset and modality; a model using macular OCT scans in highly myopic eyes reported an AUC of 0.984 on an external test set. Authors of recent reviews, however, note that data scarcity, model interpretability, and clinical validation remain open problems, and that a Food and Drug Administration (FDA) approved an automated system to review fundus images for diabetic retinopathy, a precedent that could extend to glaucoma screening.

Mechanisms of neurodegeneration beyond intraocular pressure

Elevated intraocular pressure (IOP) remains the best-established risk factor for glaucoma, but it does not account for the whole disease. Many patients continue to lose retinal ganglion cells (RGCs) and visual field after their pressure has been brought down, and optic nerve damage has been documented in people whose pressure stays within the normal range. Researchers therefore increasingly describe glaucoma as a neurodegenerative process in which several interacting pathways, of which pressure is one trigger, lead to the death of RGCs and the degeneration of their axons. Individual RGCs also differ in how sensitive they are to pressure, which helps explain why similar pressures produce different outcomes in different people.

Mechanical injury and failure of axonal transport

The axons of RGCs pass through the lamina cribrosa, a sieve-like connective tissue at the optic nerve head. Mechanical strain at this site can compress and distort the axon bundles, and the resulting injury is thought to interrupt axoplasmic flow, the movement of organelles, proteins and signalling molecules along the axon. Both anterograde transport (from cell body toward the axon terminal) and retrograde transport (back toward the cell body) are affected. Failure of axonal transport is regarded as one of the earliest detectable events in experimental models, and it may precede the degeneration of the cell body. Before outright cell death, some RGCs appear to enter a period of reduced activity and dysfunction, which may correspond to the early visual loss seen clinically. The initial trigger that sets this sequence in motion remains unidentified.

Excitotoxicity, calcium overload and mitochondrial dysfunction

Glutamate is the main excitatory neurotransmitter of the retina. When damaged or stressed cells release excess glutamate, or when the clearance of glutamate by surrounding glial cells fails, NMDA receptors on RGCs are overstimulated. The resulting influx of calcium through channels that are permeable to calcium ions can exceed the cell's buffering capacity. Calcium overload then activates enzymes that damage cellular structures and drives the mitochondria to take up calcium as well. Mitochondria in glaucomatous RGCs show impaired structure and reduced energy production, which further limits the cell's ability to maintain its ion gradients. A failing mitochondrion also leaks reactive molecules, linking energy failure directly to the oxidative injury described below. Glutamate, calcium and mitochondrial failure therefore reinforce one another rather than acting as separate insults.

Oxidative stress, vascular dysregulation and inflammation

Because the optic nerve head has a limited and sometimes fragile blood supply, episodes of reduced perfusion followed by reperfusion can generate bursts of reactive oxygen species that overwhelm the antioxidant defences of neurons. Nitric oxide and free radicals released in the retina add to this burden. Glial cells, particularly astrocytes and microglia, respond to the injury by releasing cytokines and other mediators, and chronic glial activation can sustain a low-grade inflammatory state that continues to damage neurons. Some studies suggest that brief, controlled inflammation may even support the regenerative capacity of RGCs, so the balance between harmful and protective immune responses appears to matter. Vascular dysregulation, in which the regulation of blood flow to the optic nerve head is disturbed, is considered a contributor both to the initial insult and to ongoing ischaemic stress.

Neurotrophic factor deprivation and apoptosis

The neurotrophic factor deprivation hypothesis proposes that RGCs depend on survival signals delivered from their central targets. The most studied of these is brain-derived neurotrophic factor (BDNF), which is synthesised locally in the retina and also transported backward along the axon from the brain. If axonal blockade cuts off this supply, the cell loses a key survival signal and is pushed toward apoptosis, a programmed form of cell death. Animal studies support parts of this model: retrograde transport of BDNF has been shown to be reduced in rodent and canine glaucoma models, and BDNF gene therapy can delay RGC loss. However, the protection is time-limited, and clinical translation of neurotrophic therapies has been disappointing so far. Degeneration also appears to be compartmentalised, with local self-destruct programmes in dendrites and axons that can operate somewhat independently of the cell body. These observations help explain why RGC loss can continue even after pressure has been controlled: once the cascade has started, several parallel pathways keep it going.

Medical treatment

Lowering intraocular pressure (IOP) is the only modifiable risk factor that current therapy can act on, so nearly all medical treatment aims to reduce pressure. The working target is set individually. It is usually expressed as a range that is expected to halt further damage to the visual field without compromising quality of life. Clinicians set it from the untreated pressure, the disease stage, and how quickly the patient is worsening. Several frameworks exist. One common approach aims for a 20–30% reduction from baseline in mild disease and 40–50% in moderate to severe disease. Others use fixed thresholds, such as pressures in the low teens for advanced cases. Targets are revised over time: a patient who keeps progressing needs lower pressure, while a stable elderly patient may tolerate a higher one.

Topical drug classes

Almost all antiglaucoma drugs work by either reducing aqueous humor production in the ciliary body or improving its outflow. Topical eye drops are the first line and the most widely used route.

• Prostaglandin analogues (latanoprost, travoprost, bimatoprost, tafluprost) are generally regarded as first-line agents. They act mainly by increasing uveoscleral outflow, lower IOP by roughly a quarter to a third, and are dosed once daily. Latanoprost and travoprost are prodrugs that corneal enzymes convert to their active forms. Their characteristic side effects include conjunctival redness, eyelash growth, and darkening of the iris and periocular skin.
• Beta-blockers (timolol, levobunolol, carteolol, betaxolol) block sympathetic signaling to the ciliary epithelium, which reduces cyclic AMP and lowers aqueous secretion. They have been used since the late 1970s. Because they are absorbed systemically, they can cause bradycardia, bronchospasm and other serious effects, particularly in people with asthma or heart block.
• Alpha agonists (brimonidine, apraclonidine) activate α2-adrenergic receptors, which suppresses aqueous secretion. Brimonidine may also modestly increase uveoscleral outflow. Systemic effects are generally smaller than with beta-blockers, though fatigue and dryness of the mouth are common.
• Carbonic anhydrase inhibitors (dorzolamide, brinzolamide) inhibit the enzyme in ciliary processes that drives aqueous formation. They are often combined with beta-blockers or prostaglandins.
• Rho kinase inhibitors (netarsudil and related agents) act directly on the trabecular meshwork to increase conventional outflow. Their effects on the cell structure of this tissue are also being studied for their potential to reduce fibrosis.
• Miotics (pilocarpine) and other cholinergic drugs contract the ciliary muscle, which widens the trabecular meshwork. They have largely fallen out of first-line use because they can cause blurred vision and myopia.

Oral carbonic anhydrase inhibitors

Oral acetazolamide is the best-known systemic agent. It is reserved for situations in which rapid pressure reduction is needed, such as acute angle-closure attacks before surgery, secondary glaucoma, or cases where topical drugs fail. Typical acute doses are 250 mg every four hours, sometimes preceded by a larger loading dose. In open-angle disease, daily doses are usually lower and rarely exceed 1 g. Common side effects include fatigue, tingling in the face and extremities, a metallic taste, nausea, and metabolic acidosis. Dizziness, weight loss and transient myopia are also reported. Long-term use is inappropriate in chronic angle-closure glaucoma, because it can mask rising pressure while the angle progressively closes. High-dose use has been linked to rare kidney injury, and drug-induced choroidal effusion with secondary angle closure has been described. Caution is also needed in patients with sulfonamide allergy, electrolyte disturbances, or significant kidney or liver disease.

Adherence, surface toxicity and education

Medication is effective only when taken consistently. Patients who use drops irregularly may meet their target at clinic visits yet still progress between them. Multiple daily drops, complex regimens, and difficulty instilling drops (especially in older patients) all reduce adherence. Fixed-dose combinations reduce the number of bottles and instillations, and they lower exposure to preservatives. Ocular surface problems, such as stinging, dryness and allergic reactions, are common and are often attributed to preservatives like benzalkonium chloride. These problems can prompt patients to stop treatment. For this reason, patient education on technique, timing and side effects is considered an integral part of management.

Laser and surgical interventions

Laser and surgical procedures are used when medication does not lower intraocular pressure enough, when adherence is poor, or when the disease is advanced at the time of diagnosis. Each procedure acts on a different part of the outflow pathway or on aqueous production, so the choice depends on the angle type, the disease stage, and the eye's remaining function.

Laser peripheral iridotomy (LPI) is the first-line procedure for primary angle closure. A small opening is made in the peripheral iris, which relieves pupillary block and allows the iris to flatten, widening the anterior chamber angle. Its preventive value has been tested in randomized trials. In the Zhongshan Angle-Closure Prevention study, 889 people with bilateral angle-closure suspects were randomized so that one eye was treated and the other was not. At 72 months, the incidence of angle-closure disease was 4.2 per 1000 eye-years in treated eyes versus 8.0 in untreated eyes, and the authors judged the benefit modest, so they did not recommend widespread prophylactic treatment. A 14-year follow-up reported a hazard ratio of 0.31 for progression to angle closure in treated eyes. Because iridotomy does not address every mechanism, laser peripheral iridoplasty, in which contraction burns in the iris periphery open the angle, is used as an adjunct in eyes with mixed mechanisms, though its evidence base is less mature.

Selective laser trabeculoplasty (SLT) is the main laser option for open-angle disease. It uses short pulses of a 532 nm Nd:YAG laser that are absorbed by pigmented trabecular meshwork cells, leaving neighbouring tissue largely intact. The outflow gain is thought to arise from biological remodelling, including changes in the juxtacanalicular matrix and in Schlemm's canal endothelium, rather than from mechanical damage. Typical pressure reductions are around 20 percent, and the effect is greater in eyes with higher starting pressure. The effect fades over time: in a UK real-world cohort, most eyes responded at six months but only about a quarter remained controlled at two years, and repeat treatment is generally possible.

Filtering surgery, chiefly trabeculectomy, creates a new drainage route by cutting a scleral flap and allowing aqueous to escape into the subconjunctival space beneath a conjunctival bleb. Its main weakness is scarring at the bleb, which closes the route. Antifibrotic agents such as mitomycin C (MMC) and 5-fluorouracil reduce this fibrosis and have substantially improved long-term success. Standard practice applies 0.2 mg/ml MMC for two to three minutes, and reviews have suggested that lower concentrations with standardized exposure can achieve similar pressure control with fewer complications, notably bleb leaks, hypotony and infection.

Glaucoma drainage implants, or tube shunts, such as the Ahmed and Baerveldt devices, divert aqueous to a plate placed under the conjunctiva. They are preferred when trabeculectomy has failed or is likely to fail, for example in neovascular, uveitic or congenital disease. A fibrous capsule forming around the end plate limits flow, and adjunctive MMC or anti-VEGF agents have produced mixed results. Minimally invasive glaucoma surgery (MIGS) refers to a group of microinvasive procedures, often performed alongside cataract surgery, that enhance conventional outflow through the trabecular meshwork or Schlemm's canal, or that create suprachoroidal outflow. They generally lower pressure less than trabeculectomy or tube shunts and are most suitable for mild to moderate disease.

Cyclodestructive procedures, such as transscleral cyclophotocoagulation, reduce aqueous production by damaging the ciliary body. Because they carry risks of pain, inflammation, hypotony and vision loss, they are usually reserved for advanced disease, eyes with little remaining visual potential, or cases that have failed other surgery. The choice among these options weighs the severity and rate of progression, the target pressure, the eye's remaining function, prior surgery, and the surgeon's experience. Surgical decisions are therefore individualized rather than sequential by rule.

Long-term management, prognosis and access to care

Follow-up schedules

Follow-up intervals are usually set by disease severity and by how quickly the visual field is changing. The European Glaucoma Society recommends six visual field tests in the first two years after diagnosis, because this schedule detects rapid progression sooner than yearly testing does. NICE advises intervals of 2 to 6 months for newly diagnosed patients and 6 to 12 months for stable follow-up. The American Academy of Ophthalmology recommends field testing at least once a year. In practice, adherence to these schedules is poor. A US study of 380,029 patients found that more than 75% received fewer than one field test per year. A UK multicentre audit reached a similar conclusion, finding that newly diagnosed patients typically underwent only two or three tests in their first two years.

Prognosis and the risk of blindness

Glaucoma is a slow disease, and its outcome is measured over decades. In a population-based cohort from Olmsted County, Minnesota, the estimated risk over 20 years was 27% for unilateral blindness and 9% for bilateral blindness among patients treated for glaucoma or ocular hypertension. Patients whose glaucoma was already evident at diagnosis faced much higher figures, with corresponding risks of 54% and 22%. A lifelong follow-up study of 423 patients reported that 64 patients (15.2%) became bilaterally blind from glaucoma during follow-up.

Several baseline and course-related factors predict these outcomes. The risk of blindness increased with higher intraocular pressure and with each stage of more advanced field loss at the time of diagnosis. Other studies have linked blindness to advanced glaucoma at diagnosis, fluctuation of intraocular pressure during treatment, the presence of exfoliation syndrome, and poor patient compliance. A multicentre clinical series found that mean deviation worsened by about 1.1 dB per year in eyes that later became blind, roughly five times the rate seen in controls. Involvement of the second eye also matters: unilateral blindness at presentation more than doubled the risk of bilateral blindness, according to one cited analysis. Blindness is generally defined as visual acuity of 0.05 or lower, and/or visual field loss to less than 10 degrees.

Low vision rehabilitation

For patients whose sight cannot be restored, the emphasis shifts to function. Glaucoma-related field loss often causes more disability than loss of central acuity, and patients commonly report reduced mobility. The American Academy of Ophthalmology's vision rehabilitation committee recommends referral for low vision evaluation when acuity is worse than 20/40, when contrast sensitivity is reduced, or when a peripheral or central scotoma is present. Services include an eye examination and visual function assessment, and often include a psychological assessment, employment counseling, driving fitness evaluation, and they may take place in the patient's home. Training may address mobility, orientation, eccentric viewing, assistive technology assessment and use of optical aids. Evidence for effectiveness is considered strong. One intensive inpatient programme in the US Department of Veterans Affairs system has been studied in a randomised trial setting, with a few weeks of training and access to visual assistive equipment. Despite this, referral is uncommon: in one academic centre, only 14 of 522 patients with severe open-angle glaucoma (2.7%) were referred for low vision evaluation.

Barriers to care

Access to long-term care depends heavily on the health system. Glaucoma management requires repeated visits, field testing, and continuous drug use, so costs of medication, transport and specialist time can limit follow-up, particularly in low-income settings and rural areas where ophthalmologists are scarce. The gap between recommended and actual monitoring, and the low uptake of rehabilitation services, shows that clinical guidance alone does not ensure care. Despite the positive reported outcomes of vision rehabilitation, very few glaucoma patients use visual rehabilitation services. Where universal health coverage and public health screening programmes are weak, late diagnosis and interrupted treatment are more likely, which raises the probability of advanced disease at presentation. Some national systems provide support through specialised agencies; in the United States, for instance, every state has a designated agency providing vocational rehabilitation and other disability-related services for residents who are blind or visually impaired.

History of the concept and its tools

The name comes from the ancient Greek adjective glaukos, whose likely origin lies in a word used variously to describe a sea-green or blue-gray color. Because the same root also described clouded surfaces, the label was applied to several conditions. In antiquity, glaukos was used for various eye conditions with opacity visible to the naked eye, including corneal disease and even cataract. Celsus, Rufus of Ephesus and Galen treated the disorder as a problem of the crystalline lens, and the sense of the term shifted over later centuries.

In Arabic scholarship, the Greek root was rendered as zarqaa, the word for blue. Arabic scholars translated glaukos to zarqaa, a term meaning "blue." Medieval European authors then translated these works into Latin and described the green hue of the pupil and associated it with a thickening of the anterior lens of the eye. They called the condition viriditas and did not have a method of curing it. Avicenna, among others, attributed the condition to a thickening of the lens leading to a hard eye. The optical framework of the period also came from Ibn al-Haytham, whose Book of Optics described the correct theory of vision in which the seeing process was facilitated by light rays radiating from an object to the eye. This optical theory of vision later provided the basis for examining the interior of the eye.

In the eighteenth century, the boundary between glaucoma and cataract was drawn more sharply. Michel Brisseau defined glaucoma and cataracts as two different diseases by noting that glaucoma happened deeper in the eye. English oculists such as John Taylor are credited with providing one of the most complete pre-ophthalmoscopic descriptions of glaucoma. Their work still lacked a way to see the optic nerve in a living patient, which is why the next step was decisive.

Direct examination of the fundus developed in the nineteenth century. Jan Purkinje had manufactured a makeshift ophthalmoscope using only myopic spectacles and a candle in 1823, but the instrument that became standard was Hermann von Helmholtz's. Accounts differ on the exact date, with some placing the first documented version in 1850 and others citing 1851. The device enabled clinicians to visualise the retina and optic nerve directly. Once the disc could be seen, observers noted an excavated optic neuropathy in the classic (angle-closure) glaucoma with a green pupil, and the excavation of the nerve suggested that pressure was a defining characteristic of the disorder. The ophthalmoscope thus tied the visible damage to the nerve to a pressure-based explanation.

Measuring that pressure proved a separate problem. Before the invention of tonometers, measurements of IOP were made with fingers on the upper eyelids. Von Graefe's 1862 instrument was among the first attempts at a device, but due to the lack of ophthalmic anesthesia, these tonometers were placed on the eyelid rather than the eye. Cocaine anesthesia changed this. The introduction of cocaine corneal anesthesia in 1884 by Karl Koller allowed tonometers to be applied directly to the cornea. Earlier, Adolf Weber had identified a basic flaw: the indention of the sclera and cornea displaced a sufficient quantity of intraocular fluid to alter the pressure it was intended to measure.

The solution came from the applanation principle. Armand Imbert and Adolf Fick independently showed that when the application of the tonometer produces a flat surface, forces cancel each other, and the reading of the tonometer equals the IOP. In 1905, the Norwegian ophthalmologist Hjalmar Schiøtz introduced an indentation instrument, and it was relatively cheap and portable, which made it widely adopted before the development of the Goldmann tonometer. The Goldmann applanation tonometer built on the Imbert–Fick law, and sources date its development inconsistently, giving 1948, 1954 and 1957. Goldmann's instrument established that one gram of force is equivalent to one mm Hg of intraocular pressure. Its role as a reference standard has persisted, and despite its limitations, it continues to be theoretically more precise and considered the gold standard tonometer to diagnose and manage patients with ocular hypertension and glaucoma. These instruments, together with clinical observation of the optic disc, formed the pressure-based framework that defined glaucoma through the twentieth century, including the intraocular pressure measurements discussed elsewhere in this article.

Open questions and emerging research

Neuroprotection independent of pressure

Every treatment approved for glaucoma works by lowering intraocular pressure, so the ongoing loss of retinal ganglion cells has no direct therapeutic target. Neuroprotection aims to fill that gap: agents that keep these cells alive and slow functional decline through routes other than pressure reduction. Preclinical work has produced many candidates, yet most have not translated into clinical benefit. The best-known example is memantine, an antagonist of NMDA that had been used in Alzheimer's and Parkinson's disease. Animal studies suggested it protected injured cells, but two large phase III trials that enrolled about 2,300 patients over up to 48 months did not meet their primary endpoints, and the randomized controlled design did not detect a benefit over placebo. Post-hoc analyses point to several reasons: the effect may have been too small to detect, the enrolled patients progressed slowly, and visual field measures lacked the sensitivity to capture subtle protection. Brimonidine produced some encouraging signals, but high dropout linked to ocular allergy and other design flaws kept it from wide acceptance. Consequently, there is no example of a primary outcome measure for neuroprotection which has led to FDA approval in glaucoma.

Trial design is therefore a central open question. Trials are typically run in patients who already receive pressure-lowering therapy, so any added protection must be measured against a background of treatment. Proposed remedies include adaptive designs, enriched populations and more sensitive endpoints, such as structural imaging with optical coherence tomography or functional tests with greater resolution. Researchers have also turned to other targets, including mitochondrial energy metabolism and glutamate signalling pathways, and to nicotinamide-based approaches; most of these remain at the preclinical or early clinical stage.

Cell replacement and regeneration

Retinal ganglion cells do not regenerate after injury, which is the basis for interest in transplanting replacement cells. Stem cell-derived retinal ganglion cells have been generated in culture, but previous transplantation studies showed modest success, largely because few transplanted cells survived and integrated into the host retina. The inner limiting membrane is a physical barrier: its pores are far smaller than the cells that must cross it, which impedes migration into the ganglion cell layer. A 2023 study reported that changing the local microenvironment allowed cells derived from blood-forming stem cells to become retinal ganglion cells that could migrate and survive in the adult mouse retina, although the work was done in mice. Remaining challenges include cell safety, the diversity of cell subtypes and scalable preparation methods, as well as rebuilding synaptic connections and directing axons to correct central targets. Early-phase human trials are under way, but none has demonstrated restored vision at scale.

Gene-based strategies explore the same biology from another direction. Neurotrophic factors such as BDNF and CNTF are reduced in glaucomatous eyes and normally suppress the intrinsic apoptotic pathway, so researchers have explored gene transfer to deliver these factors to the retina. Whether such approaches can be made both safe and durable in humans is not yet established.

Sustained-release drug delivery

A second line of research addresses the problem of adherence rather than biology. Topical drops must be given daily, and the reasons patients miss doses include forgetfulness, difficulty instilling drops, side effects and cost. One analysis of pharmacy claims found that patients had prostaglandin-class medication available only about 37% of days in a year. Sustained-release devices aim to deliver drug continuously from a single procedure. A biodegradable bimatoprost implant placed in the anterior chamber releases the drug over roughly four months, and a titanium travoprost implant (iDose) can last around four to five years and be exchanged once depleted. A recent meta-analysis reported that the bimatoprost implant lowered pressure effectively in patients with open-angle disease, including those with high pressures, and that its benefits can persist for months after one administration. These devices lower intraocular pressure rather than protecting neurons directly, and the authors called for longer studies of their effect on disease progression and visual outcomes.

Unresolved questions

Several gaps limit progress across all these areas. The causes of normal-tension disease, in which damage occurs at pressures in the normal range, remain unclear, and it is not known whether the same pathways drive all cases. Reliable early biomarkers are lacking, so trials cannot easily detect whether a therapy has acted before visual field loss appears. Pressure is also not the whole story: even when pressure is controlled, a substantial proportion of patients continue to lose ganglion cells, which underscores the need for approaches that work through other mechanisms. Finally, the role of machine learning and deep learning in screening and in predicting progression is being evaluated, but its clinical validation, generalizability across populations and integration into care pathways remain open.

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