Glaucoma

Glaucoma is a progressive optic neuropathy: retinal ganglion cells are lost, the retinal nerve-fibre layer becomes thinner, and the optic-nerve head develops characteristic cupping or other structural changes. As axons are damaged, the corresponding visual field is lost. This damage is irreversible, so treatment protects the vision that remains rather than restoring a field that has already disappeared. In many forms of glaucoma, resistance to aqueous-humour outflow raises intraocular pressure (IOP). Pressure-related stress at the optic nerve head contributes to axonal injury. IOP, however, is a risk measure rather than the diagnosis itself. Some people sustain the characteristic structural and functional damage with an IOP of 21 mmHg or lower; this is the pattern called normal-tension glaucoma. The early loss often affects peripheral vision before central acuity changes. A patient may therefore read an eye chart well and still have meaningful optic-nerve disease. Patients may not notice gradual field loss because the unaffected eye and the brain compensate. That quiet progression is why adherence to treatment and scheduled testing matter even when the eyes feel normal.