Glaucoma: Why the "Silent Thief of Sight" Must Be Detected Early

What is glaucoma?

Glaucoma is a group of eye conditions that damage the optic nerve - the bundle of over one million nerve fibres that carries visual information from the retina to the brain. In most cases, this damage is caused by elevated intraocular pressure (IOP), though glaucoma can progress even when pressure is within the normal range.

The optic nerve damage is cumulative and irreversible. Once nerve fibres are lost, they cannot be regenerated. This is why early detection - before symptoms appear - is so critical. By the time a patient notices vision changes, they may have already lost 30-40% of their optic nerve fibres.

Globally, glaucoma is the second leading cause of blindness after cataract, and unlike cataract, glaucoma blindness cannot be reversed with surgery. In India, an estimated 12 million people are affected, with a significant proportion undiagnosed.

Why does it have no symptoms?

In primary open-angle glaucoma - the most common form - peripheral (side) vision is affected first. The brain is remarkably good at compensating for peripheral vision loss, filling in gaps so the patient perceives a complete picture. This compensation continues until very late stages, when central vision begins to be affected and the field loss becomes obvious.

By analogy: if you close one eye right now, your peripheral vision on that side disappears entirely, yet you may not notice immediately because your brain compensates. Early glaucoma produces far subtler changes over years, which is why it escapes notice for so long.

Acute angle-closure glaucoma is a dramatic exception - it causes sudden severe eye pain, headache, nausea, halos around lights and markedly blurred vision. This is a medical emergency requiring immediate treatment, but it represents a minority of glaucoma cases.

Types of glaucoma

Who should be screened?

Because early glaucoma has no symptoms, the only way to detect it is through a comprehensive eye examination. Eye Veda recommends annual screening for anyone who:

• Is over 40 years of age
• Has a parent or sibling with glaucoma
• Has high myopia (short-sightedness above -4D)
• Has diabetes or hypertension
• Uses steroid medications (eye drops, inhaler, or tablets)
• Has previously had an eye injury

If you have no risk factors, a baseline examination is recommended at age 40 and then every 2 years. If risk factors are present, annual screening should begin earlier.

How is glaucoma diagnosed?

A comprehensive glaucoma evaluation at Eye Veda includes several complementary tests - no single test is sufficient on its own:

• Tonometry - measures intraocular pressure (IOP). Normal range is 10-21 mmHg, but glaucoma can occur at any level.
• Ophthalmoscopy - the doctor examines the optic nerve head for changes in the cup-to-disc ratio and signs of nerve fibre loss.
• Visual field testing (perimetry) - maps peripheral vision. Glaucomatous field defects have characteristic patterns that help with diagnosis and monitoring.
• Optical coherence tomography (OCT) - measures the thickness of the retinal nerve fibre layer around the optic nerve. Can detect structural loss before it appears on visual field testing.
• Pachymetry - measures central corneal thickness, which affects IOP readings and is an independent risk factor.
• Gonioscopy - examines the drainage angle to classify glaucoma type.

Treatment options

Glaucoma cannot be cured, but progression can almost always be halted or significantly slowed with appropriate treatment. The goal is to lower IOP to a level at which the optic nerve no longer deteriorates - the “target pressure” - and then maintain it there for life.

Eye drops

Medicated eye drops are the standard first-line treatment for most patients with open-angle glaucoma. Prostaglandin analogues (latanoprost, bimatoprost) are typically the first choice, lowering IOP by 25-35% with once-daily dosing. Beta-blockers, alpha agonists, and carbonic anhydrase inhibitors may be added as second or third agents. Consistency is critical - missed doses allow IOP to rise and nerve damage to resume.

Selective Laser Trabeculoplasty (SLT)

SLT uses a low-energy laser to stimulate the trabecular meshwork (the eye’s drainage tissue), improving aqueous outflow and lowering IOP. It is safe, repeatable, and effective in 70-80% of patients, often reducing or eliminating the need for drops. It is increasingly offered as a primary treatment, not just for patients who struggle with drops.

Trabeculectomy (filtering surgery)

For patients with advanced glaucoma or inadequately controlled IOP despite maximum medical therapy, trabeculectomy creates a new drainage channel under the conjunctiva. It achieves greater IOP reduction than drops or laser and can produce long-term pressure control, though it requires careful post-operative management.

Minimally invasive glaucoma surgery (MIGS)

A newer category of procedures - iStent, Hydrus, OMNI - that can be combined with cataract surgery to lower IOP with a better safety profile than trabeculectomy. Suitable for mild-to-moderate glaucoma in patients undergoing cataract surgery.

Living with glaucoma

A glaucoma diagnosis requires a long-term commitment to monitoring and treatment. Key points for patients:

• Take eye drops at the same time every day - consistency matters more than timing
• Attend all follow-up appointments, typically every 3-6 months
• Visual field tests and OCT scans are repeated annually (or more frequently) to monitor for progression
• Inform all treating doctors (including dentists and GPs) that you have glaucoma, particularly if steroids or anticholinergic medications are being considered
• Alert first-degree relatives about your diagnosis so they can be screened