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Glaucoma

Glaucoma

Pathologic optic disc cupping
In this eye, the ratio between the diameter of the physiologic cup and the diameter of entire optic disc (the cup-to-disc ratio) far exceeds the allowable limit of 0.5. Therefore, this optic disc probably has pathologic cupping, usually a sign of glaucoma.

Glaucoma
The optic disc becomes progressively cupped as axons die off. Curiously, this is the only optic nerve disorder in which severe cupping takes place; in all others, the disc simply becomes pale.

There are two other important features: the intraocular pressure is often elevated (higher than 21 mm Hg) and the visual fields show typical constriction.

Glaucoma comes in four forms: primary open-angle, secondary, congenital, and angle-closure.

Primary open-angle glaucoma is by far the most common, accounting for over 98% of all cases. It affects about 1% of adults aged over 40 years. Affected individuals are initially asymptomatic because visual acuity is spared until the disease is far advanced, and because elevated intraocular pressure causes no pain as it is chronic. A family history of glaucoma is present in about 1/5 of patients.

Elevated intraocular pressure is a factor in causing damage to the optic nerve. In normal eyes, aqueous fluid flows out through the trabecular meshwork.

In eyes with primary open-angle glaucoma, the meshwork is abnormal and blocks the normal outflow of aqueous fluid. Medical treatment uses eyedrops to improve outflow or reduce aqueous secretion. If that fails to lower pressure, surgical treatment consists of creating a hole in the eyewall between the anterior chamber and the subconjunctival space (a filtering operation) and bypassing the trabecular meshwork. Treatment is not always effective in stopping the degeneration of the optic nerve, even if pressure is normalized. To watch a narrated video of this sequence, click here.

In secondary glaucoma, damage to the meshwork is caused by trauma, inflammation, or blood. Treatment is aimed at reducing inflammation and at lowering pressure, as in primary open-angle glaucoma.

Congenital glaucoma is caused by a malformed meshwork. It presents in infancy as tearing, photophobia, red and enlarged eye, and cloudy cornea. Treatment is urgent surgery to open the meshwork.

Angle-closure glaucoma results when the iris root plugs the opening of the trabecular meshwork. This mostly occurs in older adults who have small eyes. It is impossible to predict who is at risk. It presents as an acute red eye with severe periocular pain and blurred vision. Treatment consists of creating a hole in the peripheral iris (iridotomy) with the laser or surgery. That usually forces the iris out of the way and allows aqueous to drain out normally. To watch a narrated video of this sequence, click here. If treatment of angle-closure glaucoma is delayed, the iris becomes stuck down, and laser iridotomy will not work. A filtering procedure must then be done, as in primary open-angle glaucoma.

What to do?
Refer non-urgently any patient whose optic disc shows a cup-to-disc ratio of greater than 0.5, especially if there is a family history of glaucoma.

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