Glaucoma is a group of progressive optic neuropathies characterised by damage to the optic nerve and corresponding patterns of visual-field loss, often associated with but not defined solely by intraocular pressure. The optic nerve contains retinal ganglion-cell axons that transmit visual information from the retina to the brain, and glaucoma involves loss or dysfunction of these neural elements.
Elevated intraocular pressure is a major modifiable risk factor because mechanical and vascular stresses can contribute to retinal ganglion-cell injury, but glaucoma can occur with pressures within statistically normal ranges, while some people with elevated pressure never develop optic-nerve damage. The major clinical categories include open-angle and angle-closure mechanisms, with additional forms associated with secondary causes such as inflammation, trauma, steroid exposure, developmental abnormalities or other ocular disease. Glaucoma is often asymptomatic during early stages because peripheral visual loss can develop gradually and the brain adapts to missing information. This makes detection through examination important because established optic-nerve damage generally cannot simply be restored to normal.
In the healthy eye, aqueous humour is produced primarily by the ciliary body, passes through the posterior and anterior chambers and exits through drainage pathways involving the trabecular meshwork and Schlemm's canal, with additional uveoscleral outflow. Intraocular pressure reflects the balance between aqueous production and outflow. In open-angle Glaucoma, the drainage angle remains anatomically open but resistance to aqueous outflow can increase, contributing to elevated pressure in many cases.
In angle-closure mechanisms, the drainage angle becomes narrowed or blocked, potentially producing a rapid rise in pressure. The relationship between pressure and nerve damage is complex because susceptibility varies with optic-disc anatomy, age, vascular factors, corneal properties and other biological characteristics. The lamina cribrosa, where retinal ganglion-cell axons pass through the optic nerve head, is particularly relevant to mechanical deformation and axonal injury. Glaucomatous damage is therefore not adequately described as simply “high pressure in the eye”. Pressure is a measurable risk factor and treatment target, whereas the defining pathological process concerns optic-nerve and retinal ganglion-cell loss.
Open-angle Glaucoma is often chronic and slowly progressive. Peripheral visual-field defects can develop before a person notices substantial functional impairment, and central Vision may remain relatively good until advanced stages. Optic-disc examination can reveal structural changes such as increased excavation or thinning of the neuroretinal rim, although optic-disc anatomy varies naturally between individuals. Optical coherence tomography can quantify retinal nerve fibre layer and ganglion-cell-related structures, helping detect and monitor structural loss.
Automated perimetry measures visual-field sensitivity and can identify characteristic defects corresponding to damaged retinal pathways. Repeated measurements are often more informative than one isolated test because clinicians need to determine whether structural or functional change is occurring over time. Some patients have ocular hypertension, meaning elevated intraocular pressure without demonstrable glaucomatous optic-nerve damage, while others have normal-pressure glaucoma with characteristic damage despite pressures that are not elevated by conventional measurements. These categories illustrate why diagnosis depends on multiple sources of evidence.
Angle-closure Glaucoma can behave differently and may sometimes constitute an emergency. When aqueous outflow becomes acutely obstructed, intraocular pressure can rise rapidly, causing severe eye pain, headache, blurred vision, halos around lights, nausea and vomiting. The eye may become red and the pupil can become abnormally responsive. Acute angle closure requires urgent ophthalmic treatment because prolonged extreme pressure can rapidly damage the optic nerve. Anatomical features associated with a crowded anterior segment, including a shallow anterior chamber, can increase susceptibility.
Hyperopic eyes are statistically associated with some anatomical configurations that predispose to angle closure, although refractive status alone does not determine an individual's risk. Chronic or intermittent angle closure can occur without the dramatic symptoms of an acute attack and may progressively damage the optic nerve. This contrasts with many forms of open-angle Glaucoma, which can remain silent for years.
Risk factors for Glaucoma include increasing age, family history, elevated intraocular pressure, certain ethnic and anatomical characteristics, high myopia for some forms, previous eye injury, steroid exposure and particular systemic or ocular conditions. Risk does not equal diagnosis. A person with several risk factors may have no optic-nerve damage, while another person with fewer obvious risks can develop glaucoma. Genetic susceptibility is important, and family history can justify greater awareness and monitoring.
Corneal thickness can influence interpretation of pressure measurements because some measurement techniques are affected by corneal biomechanics. Vascular factors may also influence susceptibility in certain forms, particularly normal-pressure disease. The disease can be unilateral or asymmetric, especially in secondary forms, although primary glaucomas frequently affect both eyes to differing degrees. These complexities explain why glaucoma assessment cannot be reduced to a single pressure threshold.
Treatment aims to slow or prevent further optic-nerve damage by reducing intraocular pressure to a level appropriate for the individual, even when baseline pressure is not particularly high. Topical medications can reduce aqueous production or increase outflow, and different drug classes have distinct mechanisms and contraindications. Laser procedures can improve aqueous drainage in selected forms, while surgical procedures can create alternative pathways for aqueous outflow or reduce resistance within existing drainage structures.
Treatment choice depends on glaucoma type, severity, rate of progression, pressure level, anatomy, medication tolerance and patient-specific circumstances. Because existing optic-nerve loss is generally permanent, treatment is primarily protective rather than restorative. Adherence can be difficult because eye drops may cause local or systemic adverse effects and because glaucoma may produce no symptoms to remind a person that treatment is necessary. Regular monitoring therefore remains essential even when Vision feels unchanged.
Glaucoma is often misunderstood as synonymous with blindness, but the disease exists across a spectrum of severity and can frequently be managed to reduce the likelihood of further loss when detected and treated appropriately. Another misconception is that normal eye pressure excludes glaucoma. It does not. Conversely, elevated pressure alone does not establish the diagnosis.
Glaucoma is also distinct from Cataracts because cataracts cloud the lens and can usually be treated surgically with substantial visual improvement, whereas glaucomatous optic-nerve damage is neural tissue loss and cannot generally be reversed by lowering pressure. It is distinct from Macular Degeneration because the principal neural structure affected is the optic nerve rather than the macula. These distinctions matter because symptoms, examination findings, treatment strategies and prognoses differ substantially among the conditions.
The public-health significance of Glaucoma arises from its often silent progression and the irreversible nature of established neural damage. Regular eye examinations can detect structural or pressure-related abnormalities before severe functional impairment becomes apparent. Early detection does not guarantee that progression can be eliminated, but it allows risk assessment and treatment to begin before more extensive damage occurs. Modern glaucoma care increasingly combines pressure measurements, optic-nerve examination, retinal imaging, visual-field testing and longitudinal analysis.
Artificial-intelligence methods are also being investigated for identifying structural patterns and predicting progression, although clinical interpretation remains essential. The term Glaucoma therefore describes a family of optic-nerve diseases rather than a single pressure disorder, and understanding that distinction is central to accurate diagnosis, monitoring and communication.
