Glaucoma

</div> Glaucoma is an eye disease that is defined as a characteristic optic neuropathy, or disease of the optic nerve. The most common cause of glaucoma is increased intraocular pressure. There is no set threshold for intraocular pressure that causes glaucoma - while one person may develop nerve damage at a relatively low pressure, another person may have high eye pressures for years and yet never develop damage. Untreated glaucoma leads to permanent damage of the optic disc of the retina and resultant visual field loss, which can progress to blindness.

There are many types of glaucoma. The most common type, open angle glaucoma, frequently has no symptoms and has been nicknamed "the thief of sight". It is probably caused by a relative obstruction on the outflow of aqueous humour from the eye. Another type, acute angle closure glaucoma, is characterized by an acute rise in the intraocular pressure. This occurs in susceptible eyes when the pupil dilates and blocks the flow of fluid through it, leading to the peripheral iris blocking the trabecular meshwork, which is located at the junction of the peripheral iris and the cornea and through which the aqueous humour drains. Acute angle closure glaucoma can cause pain and blurred vision, and may lead to irreversible loss of vision within a short time. This is an ocular emergency requiring immediate treatment. Many people with glaucoma experience halos around bright lights as well as the loss of sight characterized by the disease.

Risk factors and diagnosis

People with a family history of glaucoma have about a six percent chance of developing glaucoma. Diabetics and Blacks are more prone to open angle glaucoma, and Asians are more prone to develop angle closure glaucoma. Ideally, everyone over the age of thirty-five should be checked for glaucoma, with the frequency of the checkups increasing with age.

Screening for glaucoma is usually performed as part of a standard eye examination performed by an ophthalmologist or optometrist. Testing for glaucoma should include measurement of the intraocular pressure, as well as examination of the optic nerve to look for any damage to it. If there is any suspicion of damage to the optic nerve, a formal visual field test should be performed. Scanning laser ophthalmoscopy may also be performed

Treatment

Although intraocular pressure is only one of the causes of glaucoma, at the current time lowering it is the mainstay of glaucoma treatment.

Drugs

High intraocular pressure can be treated with eye drops that lower the eye pressure. There are several different classes of medications to treat glaucoma. There are several different medications in each class. Marijuana has been suggested to lower the intraocular pressure in some eyes in a few studies, but the results are not reproducible. It has not been shown to be an effective treatment for glaucoma. A plant called jaborandi, however, has been known to prevent glaucoma in its early stages. The jaborandi's leaves secrete an oil-like substance that, if applied to the surface of the eye, usually results in a lowering of the intraocular pressure.

Surgery

Both laser and conventional surgeries are performed to treat glaucoma. Laser trabeculoplasty may be used to treat open angle glaucoma. An argon or Nd:YAG laser spot is aimed at the trabecular meshwork to stimulate opening of the mesh to allow more outflow of aqueous fluid. Laser peripheral iridectomy may be used in patients susceptible to angle closure glaucoma. In it, the laser is aimed at the iris to make an opening in it. This allows a new channel for fluid to flow when the usual channel through the dilated pupil is blocked.

The most common conventional surgery performed for glaucoma is the trabeculectomy. Here, a partial thickness flap is made in the scleral wall of the eye, and a window opening made under the flap to remove a portion of the trabecular meshwork. The scleral flap is then sutured loosely back in place. This allows fluid to flow out of the eye through this opening, resulting in lowered intraocular pressure.

There are also several different small tubes that are inserted into the anterior chamber of the eye and out underneath the conjucctiva to allow flow of fluid out of the eye.

Complications

While glaucoma may or may not have distinct symptoms, an almost inevitable complication of glaucoma is vision loss. Visual loss from glaucoma first affects peripheral vision. Early vision loss is subtle, and is not noticed by the patient. Moderate to severe vision loss may be noticed by the patient by checking his peripheral vision thoroughly. This can be done by closing one eye and examining all four corners of the visual field for clarity and sharpness, then repeating with the other eye closed. All too often, the patient does not notice the loss of vision until he experiences "tunnel vision". If the disease is not treated, the visual field will become more and more narrow, obscuring central vision, and finally progressing to blindness in the affected eye(s).

Visual loss related to glaucoma is irreversible, but can be prevented or slowed by treatment. If you suspect you may have glaucoma or have any risk factors for it, an appointment with an ophthalmologist is indicated.