Short answer
Glaucoma is damage to the optic nerve, and its main risk factor is high eye pressure. Lost nerve fibres do not come back, but the course of the disease can be stopped if the pressure is brought down in time. Because early glaucoma produces no symptoms, there is no way to find it other than by measuring: eye pressure, corneal thickness, the visual field and an optic nerve OCT. High pressure alone is not yet glaucoma, and normal pressure does not rule it out.
Glaucoma is one of the leading causes of permanent blindness worldwide. Often referred to as the silent thief of sight, glaucoma is a group of progressive eye conditions that damage the eye's main information cable, the optic nerve. Because early glaucoma usually causes no pain, redness or blurry central vision, thousands of people have the condition without realising it until significant vision is permanently lost.
What intraocular pressure is and how it damages vision
To understand glaucoma, imagine the eye as a small balloon filled with fluid. The front part of the eye constantly produces a clear fluid called aqueous humor. This fluid flows out of the eye through a tiny mesh-like drain called the trabecular meshwork.
In a healthy eye, fluid production and drainage stay in balance, maintaining a safe intraocular pressure of 10 to 21 mmHg. That pressure is what keeps the eye in its proper shape and holds its optics steady.
If the drainage meshwork becomes clogged, fluid builds up inside the eye and pressure rises. The increased pressure presses directly against the delicate optic nerve fibres at the back of the eye and disturbs their blood supply.
The optic nerve is made up of about 1.2 million fine nerve fibres carrying visual information from the retina to the brain. Sustained high pressure or poor blood supply causes those fibres to waste away. Because optic nerve fibres cannot regenerate, vision loss from glaucoma is permanent.
High eye pressure is not the same as glaucoma
- Ocular hypertension: high pressure without damagePressure can be 23 to 25 mmHg while the optic nerve and the visual field are intact. That is not glaucoma, but it needs regular review.
- Normal-tension glaucomaIn roughly 20 to 30% of patients with glaucoma, pressure stays inside the normal range below 21 mmHg throughout. The nerve is unusually sensitive, or its microcirculation is impaired — through low blood pressure, microvascular disease or vasospasm. This is why measuring pressure alone is not enough to diagnose glaucoma.
Main types of glaucoma
Primary open-angle glaucoma · about 85 to 90% of all cases
Mechanism. The drainage angle stays anatomically open, but the trabecular meshwork clogs microscopically and loses permeability over the years.
Course. It develops slowly and invisibly over years. There are no symptoms at all until the peripheral field narrows noticeably — tunnel vision.
Angle-closure glaucoma · rarer, but potentially very dangerous
Mechanism. The iris moves forward and physically blocks the drainage angle and the outflow channel.
Course. In an acute attack, pressure spikes to 40 to 60 mmHg or higher. This is an emergency that needs care within hours, not days.
An acute attack is an emergency
Sudden, severe eye pain radiating to the same side of the head. A visibly red eye. Vision blurring quickly. Rainbow halos around lights. Nausea and vomiting.
This needs emergency ophthalmic care within hours, not days, to avoid permanent vision loss.
Who is at risk
- Age. Risk rises noticeably after 40 and sharply after 60.
- Family history. Glaucoma in a parent, brother or sister raises the risk 4 to 9 times.
- High refractive error. High myopia above -6.0 D raises the risk of open-angle glaucoma; high hyperopia raises the risk of angle closure.
- Thin cornea. A corneal thickness under 520 to 530 microns carries a higher risk of optic nerve damage.
- Medical conditions and medication. Diabetes, high blood pressure, cardiovascular disease, and long-term corticosteroid use as drops or tablets.
How glaucoma is diagnosed
Because early glaucoma produces no symptoms, the only way to find it is a regular, comprehensive examination. Four core tests are used, and none of them replaces the others.
- Tonometry: measuring eye pressurePressure is measured with a non-contact air puff, with an iCare tonometer, or with Goldmann applanation tonometry, the gold standard.
- Pachymetry: measuring corneal thicknessCorneal thickness directly affects the tonometer reading. A thin cornea reads lower than the true pressure, a thick cornea reads higher. Without this measurement the pressure number can mislead.
- Perimetry: visual field testingComputerised perimetry maps light sensitivity and picks up early field defects and blind spots the person has not yet noticed.
- Optic nerve OCTA high-precision 3D scan that measures the optic disc and the retinal nerve fibre layer, the RNFL, to the micron. OCT detects nerve fibre loss years before it shows up as a visual field defect.
Treatment and keeping it under control
The damage glaucoma has already done cannot be reversed, but the course of the disease can be stopped or substantially slowed by lowering pressure to an individual target.
- Prescription eye drops. First line. Drops either reduce fluid production, such as beta blockers, or improve outflow, such as prostaglandin analogues. They have to be used every day — a missed drop is missed treatment.
- Selective laser trabeculoplasty (SLT). A painless outpatient laser treatment that stimulates the cells of the drainage angle and improves natural outflow. In current guidance SLT is increasingly a first-line option, before daily drops.
- Surgery. When drops and laser are not enough, surgery — trabeculectomy or minimally invasive glaucoma surgery, MIGS — creates a new drainage channel.
What KSA does, and how often to come
KSA's Audit eye examination always measures eye pressure and corneal thickness and maps the cornea and the retina. Diagnosed glaucoma is a contraindication for laser vision correction, but this examination is how early warning signs get found in the first place.
Glaucoma monitoring
In glaucoma the outcome is not decided by a single measurement but by a series of them: whether the number holds still or moves. That is what KSA's glaucoma monitoring programme is for — four visits a year, pressure and corneal thickness at every visit, OCT of the optic nerve and ganglion cells four times a year, visual field testing twice a year, anterior chamber angle measurement once a year, and a progression analysis by the doctor at every visit.
It is built for people with suspected or diagnosed glaucoma, and for those with glaucoma in the family.
Suggested check-up intervals. Ages 18 to 39, every 2 to 3 years. Ages 40 to 59, every 1 to 2 years. From 60, or in a glaucoma risk group, every year.