Glaucoma refers to a group of optic nerve diseases that can cause visual field loss. Abnormally high pressure within the eye is a risk factor, but glaucoma can occur with normal eye pressure. Eye pressure is determined by the rate of fluid production and drainage in the eye. Two major types of glaucoma are primary open-angle glaucoma (POAG) and angle-closure glaucoma. POAG is a common disease that is often related to genetic influences and is more likely to affect older individuals and those of African descent.

How does glaucoma affect the eye?

Glaucoma is a condition arising from increased pressure within the eye, which is caused by the blockage of aqueous humor flow. This fluid, produced by the ciliary body, normally flows through the posterior chamber, into the anterior chamber, and then drains into blood vessels via the canal of Schlemm. When this flow is blocked, pressure increases and is transmitted to the optic nerve head and retina, potentially causing vision impairment. There are two main types of glaucoma: chronic, where the blockage is continuous, and acute, or narrow-angle, where the iris blocks the canal of Schlemm. Chronic glaucoma often lacks early symptoms, while acute glaucoma can cause pain, headaches, and visual disturbances.

What causes increased pressure in the eye during glaucoma?

Glaucoma is a group of eye diseases impacting the optic nerve and causing vision loss. Elevated intraocular pressure is a significant risk factor, though not definitive for the disease. The ciliary body produces aqueous humor, which maintains eye pressure and drains through specialized channels at the iris base. Blockage of these channels causes increased eye pressure. In primary open-angle glaucoma, the outflow channels may degenerate, while angle-closure glaucoma involves the iris blocking the trabecular meshwork. This obstruction prevents aqueous humor from draining, causing a pressure increase that can damage the retina and result in blindness.

Which parts of the eye are damaged by glaucoma?

Glaucoma damages the optic nerve and retinal nerve fibers, resulting in vision loss. Elevated intraocular pressure is a risk factor, harming the optic nerve and retinal ganglion cells. Primary open-angle glaucoma (POAG) damages the optic nerve and affects peripheral vision, while angle-closure glaucoma can block aqueous humor outflow through the trabecular meshwork, increasing pressure and causing pain and vision deterioration. In congenital glaucoma, the cornea may become clouded and enlarged.

How can glaucoma lead to vision loss?

Glaucoma is a condition that arises from increased pressure within the eye, which is caused by a blockage of aqueous humor flow. The increased pressure in the eye leads to optic nerve damage, resulting in visual field loss. If this intraocular pressure remains high for an extended period, retinal nerve fibers may atrophy, causing a loss of visual function. There are typically no symptoms in the early stages, and the slow, progressive optic nerve damage does not cause pain. Vision loss from glaucoma cannot be restored, so early diagnosis is critical to prevent further vision loss.

Why is early detection important in treating glaucoma?

Early detection of glaucoma is crucial because vision loss from glaucoma cannot be restored. The symptoms of primary open-angle glaucoma (POAG) are often absent in the early stages, as the slow optic nerve damage doesn't cause pain, and initial visual loss affects peripheral vision. By the time central vision is affected, the disease is advanced. Early diagnosis, often through simple intraocular pressure measurement, is therefore of great importance, because successful treatment can only prevent further vision loss.

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Top Questions

What is glaucoma?
Glaucoma refers to a group of optic nerve diseases that can cause visual field loss. Abnormally high pressure within the eye is a risk factor, but glaucoma can occur with normal eye pressure. Eye pressure is determined by the rate of fluid production and drainage in the eye.

Two major types of glaucoma are primary open-angle glaucoma (POAG) and angle-closure glaucoma. POAG is a common disease that is often related to genetic influences and is more likely to affect older individuals and those of African descent.
1 Britannica Source
1. eye disease: Glaucoma
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How does glaucoma affect the eye?
Glaucoma is a condition arising from increased pressure within the eye, which is caused by the blockage of aqueous humor flow. This fluid, produced by the ciliary body, normally flows through the posterior chamber, into the anterior chamber, and then drains into blood vessels via the canal of Schlemm.

When this flow is blocked, pressure increases and is transmitted to the optic nerve head and retina, potentially causing vision impairment. There are two main types of glaucoma: chronic, where the blockage is continuous, and acute, or narrow-angle, where the iris blocks the canal of Schlemm. Chronic glaucoma often lacks early symptoms, while acute glaucoma can cause pain, headaches, and visual disturbances.
2 Britannica Sources
1. eye disease: Glaucoma
2. glaucoma
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What causes increased pressure in the eye during glaucoma?
Glaucoma is a group of eye diseases impacting the optic nerve and causing vision loss. Elevated intraocular pressure is a significant risk factor, though not definitive for the disease.

The ciliary body produces aqueous humor, which maintains eye pressure and drains through specialized channels at the iris base. Blockage of these channels causes increased eye pressure. In primary open-angle glaucoma, the outflow channels may degenerate, while angle-closure glaucoma involves the iris blocking the trabecular meshwork. This obstruction prevents aqueous humor from draining, causing a pressure increase that can damage the retina and result in blindness.
2 Britannica Sources
1. human eye: The aqueous humour
2. eye disease: Glaucoma
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Which parts of the eye are damaged by glaucoma?
Glaucoma damages the optic nerve and retinal nerve fibers, resulting in vision loss. Elevated intraocular pressure is a risk factor, harming the optic nerve and retinal ganglion cells. Primary open-angle glaucoma (POAG) damages the optic nerve and affects peripheral vision, while angle-closure glaucoma can block aqueous humor outflow through the trabecular meshwork, increasing pressure and causing pain and vision deterioration. In congenital glaucoma, the cornea may become clouded and enlarged.
1 Britannica Source
1. eye disease: Glaucoma
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How can glaucoma lead to vision loss?
Glaucoma is a condition that arises from increased pressure within the eye, which is caused by a blockage of aqueous humor flow. The increased pressure in the eye leads to optic nerve damage, resulting in visual field loss. If this intraocular pressure remains high for an extended period, retinal nerve fibers may atrophy, causing a loss of visual function. There are typically no symptoms in the early stages, and the slow, progressive optic nerve damage does not cause pain. Vision loss from glaucoma cannot be restored, so early diagnosis is critical to prevent further vision loss.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why is early detection important in treating glaucoma?
Early detection of glaucoma is crucial because vision loss from glaucoma cannot be restored. The symptoms of primary open-angle glaucoma (POAG) are often absent in the early stages, as the slow optic nerve damage doesn't cause pain, and initial visual loss affects peripheral vision. By the time central vision is affected, the disease is advanced. Early diagnosis, often through simple intraocular pressure measurement, is therefore of great importance, because successful treatment can only prevent further vision loss.
2 Britannica Sources
1. eye disease: Glaucoma
2. glaucoma
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glaucoma, disease caused by an increase in pressure within the eye as a result of blockage of the flow of aqueous humour, a watery fluid produced by the ciliary body. (The ciliary body is a ring of tissue directly behind the outer rim of the iris; besides being the source of aqueous humour, it contains the muscle that flattens the curvature of the lens for far vision.) The normal flow of the aqueous humour is (1) from the ciliary body into the posterior chamber, a narrow space bounded in front by the iris, on its outer side by the ciliary body, and in back by the lens and the vitreous body, a jelly-like substance that occupies a major part of the eyeball; (2) from the posterior chamber through the pupil into the anterior chamber, the space in front of the lens and the iris and in back of the transparent window formed by the cornea; and (3) from the anterior chamber through a sievelike layer of tissue in the lining of the eyeball at the outer periphery of the iris into a circular channel, the canal of Schlemm, from which the aqueous humour flows (by way of vessels called aqueous veins) into blood vessels. Blockage of the aqueous humour flow causes increased pressure in the posterior chamber, and this pressure is transmitted by way of the vitreous to the optic nerve head and the retina. Abnormally high intraocular pressure that is unrelieved causes vision impairment.

There are two types of blockage that result in glaucoma. (1) The blockage may occur in the porous tissue between the anterior chamber and the canal of Schlemm, in the canal itself, or in the aqueous veins. This blockage is continuous, and the effect is chronic glaucoma. (2) In persons in whom the angle at the periphery of the anterior chamber is acute—i.e., in whom the outer rim of the iris is close to the wall of the eyeball—the pressure of aqueous humour upon the back of the iris may force the outer part of the iris against the wall, so as to cover the outlet into the canal of Schlemm. Glaucoma caused by this type of obstruction is called acute or narrow-angle glaucoma. When the pupil contracts, as during sleep, it tends to pull the iris away from the entrance into the canal of Schlemm and allow passage of aqueous humour, so that the high intraocular pressure may be intermittent in this type of blockage.

Chronic glaucoma does not cause symptoms in its early stages, and it is diagnosed by observation of the abnormally high intraocular pressure or the physical effects of abnormal pressure upon the optic disk (the point where the optic nerve leaves the eyeball). Treatment is primarily medical—the reduction of intraocular pressure by means of drugs that contract the pupil (miotic drugs) and allow greater outflow of the aqueous humour.

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Narrow-angle glaucoma causes pain in the eye, headaches, and sometimes nausea and vomiting. The affected person may see halos around lights. Treatment of an acute attack is similar to that of chronic glaucoma, but permanent elimination of the high pressure requires surgery; i.e., an opening is cut through the iris at its outer periphery to allow passage of the aqueous humour.

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