What glaucoma is
Glaucoma is damage to the optic nerve, the cable carrying visual information from the retina to the brain. In most cases the damage is driven by pressure inside the eye being too high for that particular optic nerve to tolerate.
The eye continuously produces fluid and drains it. If drainage is impaired, pressure rises. The nerve fibres most vulnerable to that pressure are the ones carrying peripheral vision, which is why glaucoma characteristically eats away at the edges of the visual field first and reaches central vision late.
The critical fact about glaucoma is that the loss is permanent. There is no treatment that regenerates the optic nerve. Everything that is done is done to protect what remains.
Why it is so often caught late
Open-angle glaucoma, the common form, has no pain, no redness and no early blurring. Peripheral loss creeps inward slowly, and because both eyes overlap and the brain fills in the gaps, people genuinely do not perceive it. Patients routinely arrive having lost a large part of their field while insisting their vision is fine — and from their point of view, it is.
Angle-closure glaucoma is the exception. An acute attack causes severe eye pain, headache, nausea, blurred vision and haloes around lights, with a red eye. That is an emergency and needs to be seen immediately.
Who is at higher risk
- Age over 40
- A parent or sibling with glaucoma
- Diabetes
- High myopia
- Long-term steroid use, including eye drops and inhalers
- Previous eye injury or eye surgery
- Thin corneas or an already raised eye pressure
How it is diagnosed
No single test diagnoses glaucoma. The picture is built from several.
Intraocular pressure is measured, but it is one input rather than the answer — a normal reading does not exclude glaucoma, and a raised reading does not confirm it.
Optic nerve examination looks at the nerve head for the cupping and thinning that indicate damage.
Visual field testing on the Humphrey Field Analyzer maps the sensitivity of your peripheral vision point by point. It is the standard for detecting and, more importantly, tracking field loss over time. A single field test establishes a baseline; the value comes from comparing them across years.
OCT scanning measures the thickness of the retinal nerve fibre layer, and can show thinning before it appears on the visual field.
Gonioscopy examines the drainage angle to establish which type of glaucoma is present, which determines the treatment.
How it is treated
Eye drops are the usual first step, lowering pressure either by reducing fluid production or improving drainage. They work only while they are being used, and the commonest reason glaucoma progresses despite treatment is drops being used irregularly or stopped once the patient feels fine. Since glaucoma never makes you feel unwell, “feeling fine” carries no information.
Laser treatment can improve drainage in open-angle glaucoma, or create an opening in the iris to prevent or relieve angle closure.
Surgery creates a new drainage route and is used where drops and laser have not achieved a safe pressure.
The target pressure is set individually, based on how much damage has already occurred and how fast it is progressing. It is reviewed as the disease is followed.
Follow-up is the treatment
Glaucoma care is not an episode, it is a long relationship. Pressure checks, periodic visual fields and OCT scans are what reveal whether the current treatment is actually holding, and the only way to detect slow progression is to compare tests taken years apart.
If you have been diagnosed with glaucoma and have drifted out of follow-up, the useful thing to do is to come back and re-establish a baseline. Vision already lost will not return, but the remaining field is still worth protecting.