Glaucoma is one of the world’s leading causes of blindness. But if caught in time, the disease can usually be controlled and loss of vision prevented. The glaucoma services unit at Prems’ Eye Clinic is dedicated to fighting glaucoma through patient education and community outreach. Every year,millions of people worldwide go blind from Glaucoma. Just what is this disease and what can be done about it?

Glaucoma is a group of conditions in which the optic nerve cells in the back of the eye have died at least partly due to pressure in the eye (intra-ocular pressure) exerted by the fluid in the eye (aqueous humor ) which is too high for the nerve cells in that particular eye to tolerate. The optic nerve cells’ job is to transform the light entering the eye into electrical impulses that can be understood by the brain. If enough of these cells die, then vision will be lost.

Normal Healthy Optic Disk	Glaucomatic Optic Disk

1. Open-angle and
2. Angle-closure.

Open-angle or chronic glaucoma accounts for 80 to 85% of all cases and is due to an obstruction in the drainage system of the eye.

Angle-closure glaucoma is a much rarer but very severe, acute form of the disease, since it can cause blindness in 24 to 48 hours if not treated. It results from poor access to the drainage system in the eye and is referred to as angle-closure because the angle formed by the cornea and iris becomes greatly reduced.

1.Open-angle Glaucoma

a. Primary

Chronic or primary open-angle glaucoma is the most common of adult glaucomas. People with this type of glaucoma often do not show any symptoms and only detect their glaucoma through a routine eye exam. Its exact cause is unknown but is believed to be linked to a blockage of the outflow of fluid (aqueous humor) from the trabecular meshwork.

b. Secondary

Glaucoma is classified as secondary when the condition is attributed to another disorder or condition affecting the structure or function of the eye. For example, persons with mature cataracts or persons undergoing long-term steroid therapy may develop secondary open-angle glaucoma.

Primary open angle glaucoma (POAG)

It is the most common form of glaucoma. It occurs mainly in the over 50 age group and can be hereditary.

Symptoms:

There are no symptoms associated with POAG. It is painless, and the patient often does not realise that he or she is slowly loosing vision until the later stage of the disease. However, subtle symptoms like - frequent change of glasses, delayed dark adaptation, stamping, dashing against objects can point towards very early glaucoma. By the time vision is impaired, the damage is irreversible.

Pathogenesis:

In POAG, there is no visible anomaly of the trabecular meshwork. It is believed that something is wrong with the ability of the meshwork to carry out their normal function.

Average IOP (intraocular pressure) in a normal population is 8-21 mm Hg. A pressure higher than this is considered to be suspicious and possibly abnormal. However, some people do tolerate even higher eye pressures without any damage to their eyes (ocular hypertension). What makes one person to develop damage while another does not is a topic of active research.

As we discussed earlier, this increased pressure can ultimately destroy the optic nerve cells. Once a sufficient number of nerve cells are destroyed, ‘blind spots’ begin to form in the field of vision- first in the peripheral field or the outer sides of the field of vision and then central vision or ‘seeing’ is affected. Once visual loss occurs, it is irreversible because once the nerve cells are dead, nothing can restore them at the present time.
So the earlier glaucoma is detected the better.

Normal Tension Glaucoma:

Normal tension or low tension glaucoma is characterised by progressive optic nerve damage and visual field loss with a normal intra-ocular pressure.

2. Angle-closure Glaucoma

a. Primary

This type of glaucoma occurs when the iris blocks the outflow of fluid through the trabecular meshwork because of a structural abnormality in the eye. A sudden rise in intraocular pressure occurs, with dilatation of the pupil. This causes severe pain in the eye and face, as well as other symptoms, such as nausea, vomiting, colored haloes around lights, and loss of vision.

b. Secondary

Secondary angle-closure glaucoma can occur when the Ciliary body or lens becomes swollen and pushes the iris against the trabecular meshwork. This type of glaucoma can occur in patients with diabetic retinopathy, for example.

Can be inherited more common in people of Asian descent and hypermetropes (far sighted).
In people with tendency to angle closure glaucoma the angle of the eye (drainage site / channel) is narrower than average. The narrower the angle, the less the ability of aqueous humor to pass freely through the angle. When this angle becomes completely blocked, an angle-closure attack (acute glaucoma) results.

Symptoms:

Symptoms in this stage can be intermittent headache, brow ache, blurred vision, seeing colored haloes etc.,

Acute Glaucoma:

Symptoms:

Unlike POAG, in acute glaucoma, IOP rises suddenly and is painful enough at times to cause nausea and vomiting.The eye becomes red, the cornea swells and clouds and the patient may see haloes around lights and experience blurred vision.Most of these sudden attacks occur when the pupil dilates as in darkened rooms, movie theatres, in fear or anxiety and with a variety of drugs.


Treatment:

This needs immediate treatment to prevent permanent loss of eye sight. An acute attack can be stopped with a combination of drops which constrict the pupil, and drugs which help reduce the eye’s fluid production. As soon as the IOP has dropped to a safe level, an yag iridotomy is performed.. This procedure can be performed in the other eye as well as a preventive measure.

Routine examinations using a technique called gonioscopy can predict one’s chances of developing an acute attack.