If I could persuade every adult over 40 in Kolkata to do one thing for their eye health, it would be this: get your eye pressure and optic nerve checked. Not because most of them will have glaucoma — but because those who do almost certainly will not know it.
Glaucoma is irreversible. Unlike a cataract, where the clouding can be removed and vision restored, optic nerve damage from glaucoma cannot be undone. The nerve fibres that are lost are lost permanently. This is what makes early detection so critical — and what makes complacency so costly.
What Is Glaucoma?
Glaucoma is not a single disease but a group of conditions that damage the optic nerve — the cable that transmits visual information from the eye to the brain. In most cases, this damage is associated with elevated intraocular pressure (IOP), though a significant proportion of glaucoma patients have "normal tension glaucoma" where pressure appears normal but the nerve is still being damaged.
The optic nerve is made up of approximately 1.2 million nerve fibres. Glaucoma destroys these fibres progressively, beginning at the periphery (peripheral vision) and moving inward. By the time a patient notices central vision loss, they may have already lost 40–50% of their optic nerve fibres. That loss is permanent.
The brain is remarkably good at compensating for peripheral vision loss by "filling in" gaps. Most patients with moderate glaucoma genuinely cannot tell that anything is wrong. The absence of symptoms is not reassurance — it is the danger.
Who Is Most at Risk in India?
India has one of the highest burdens of glaucoma in the world — estimated at over 12 million patients, with the majority undiagnosed. Specific risk factors include:
- Age over 40 — risk increases significantly each decade after 40
- Family history — first-degree relatives of glaucoma patients have a 4–9× higher risk
- High myopia (short-sightedness) — particularly myopia greater than -6.00 D
- Diabetes — associated with both open-angle glaucoma and neovascular glaucoma
- History of eye injury or previous eye surgery
- Long-term steroid use — both eye drops and systemic steroids can raise intraocular pressure
- Thin central corneal thickness — a structural risk factor for optic nerve vulnerability
If you have any of these risk factors and have never had a glaucoma screening, please prioritise it. The earlier it is detected, the easier it is to control.
The Two Main Types
Primary Open-Angle Glaucoma (POAG)
The most common type, accounting for 70–80% of cases. The drainage angle of the eye appears open, but drainage is impaired at a microscopic level. Intraocular pressure rises gradually and silently. Peripheral vision is lost slowly over years. Most patients have no symptoms until advanced disease. This is the type that most patients are referring to when they say "glaucoma."
Angle-Closure Glaucoma
More common in South and East Asian populations than in European populations, making it particularly relevant in India. The drainage angle is physically narrowed or closed, causing acute or chronic pressure elevation. An acute attack — called acute angle-closure glaucoma — is a genuine emergency: sudden severe eye pain, headache, nausea, seeing rainbow halos, and dramatically blurred vision. This requires same-day treatment to prevent permanent vision loss. If you or anyone you know experiences these symptoms, go to an eye casualty immediately.
What a Glaucoma Screening Involves
A comprehensive glaucoma evaluation at The Eye Clinic includes:
Intraocular pressure measurement (tonometry)
Using a non-contact tonometer ("air puff") or Goldmann applanation tonometry. Note: a single normal pressure reading does not rule out glaucoma — pressure fluctuates and normal-tension glaucoma exists.
Optic nerve examination
Dilated fundus examination to directly visualise the optic nerve head and assess the cup-to-disc ratio — the key structural indicator of glaucomatous damage. This is the most important single test.
Visual field testing (perimetry)
A computerised test that maps the entire visual field, detecting the characteristic patterns of field loss caused by glaucoma. Requires patient cooperation and typically takes 10–15 minutes per eye.
Gonioscopy (angle examination)
A lens placed on the anaesthetised eye allows direct visualisation of the drainage angle — critical for distinguishing open-angle from angle-closure disease and guiding treatment choice.
Corneal thickness (pachymetry)
Thin corneas are associated with higher risk and may cause tonometers to underestimate true intraocular pressure. Pachymetry corrects for this and refines risk assessment.
Treatment: Controlling What Cannot Be Reversed
Glaucoma cannot be cured, but it can be controlled. The goal of treatment is to lower intraocular pressure sufficiently to halt — or dramatically slow — optic nerve damage. Options include:
- Eye drops — the first line of treatment for most patients. Prostaglandin analogues, beta-blockers, and carbonic anhydrase inhibitors lower pressure through different mechanisms. Compliance with daily drops is critical.
- Laser trabeculoplasty (SLT) — a quick, painless in-office laser procedure that improves drainage through the trabecular meshwork. Often used instead of drops as first-line therapy or when drops are not tolerated. At The Eye Clinic, we perform SLT with the latest generation laser systems.
- Laser iridotomy — for angle-closure glaucoma, a small hole is made in the iris with a laser to allow fluid to bypass the blockage. This is highly effective and permanently protective against acute attacks.
- Surgical options — trabeculectomy and tube-shunt procedures for advanced disease not controlled by drops or laser.
"Treating glaucoma is like maintaining a building — regular monitoring, timely maintenance, and the right interventions prevent catastrophic failure. Neglect the building and you lose it."
— Dr. Swati Agarwal, Gold Medalist Eye SurgeonLiving With Glaucoma
A glaucoma diagnosis is not a crisis — but it is a lifelong commitment to monitoring and treatment. Patients who faithfully use their drops, attend their follow-up appointments, and report any changes in vision do very well. The majority retain functional vision throughout their lives.
What we must avoid, above all, is the patient who is diagnosed, prescribed drops, feels no different with or without them, and quietly stops using them. With glaucoma, you will feel exactly the same as the nerve continues to die. The drops do not improve your vision — they prevent it from deteriorating. That distinction is one of the most important things I explain to every newly diagnosed patient.