Basics of Glaucoma

Basics of Glaucoma

OVERVIEW

Glaucoma is the second-leading cause of blindness in the world today

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According to estimates, 60.5

million people throughout the world suffer from the disease, and this number will increase to 79.6 million

people by 2020. Glaucoma currently affects more than 4 million Americans, 3 percent of them blind from

the disease. Glaucoma represents 9-12 percent of blindness in the United States

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Glaucoma is most often detected during a routine exam, as most patients have no symptoms until the

disease has caused some peripheral vision loss. It is for this reason that glaucoma has earned the

nickname “The Sneak Thief of Sight.” Early detection is important, as most cases of glaucoma can be

treated effectively. However, once vision is lost as a result of glaucoma, it is irreversible. Eye care

personnel provide important contributions in the care and education of glaucoma patients with the

ultimate goal of reducing vision loss.

This course is designed to define glaucoma, identify the different types, review the battery of testing

required in diagnosis, and to discuss the methods of treating glaucoma, both medically and surgically.

DEFINITION OF GLAUCOMA

The term “glaucoma” refers to a group of diseases that have in common a characteristic optic neuropathy

with associated visual field loss for which elevated intraocular pressure (IOP) is one of the primary risk

factors.

Many of the causes of glaucoma remain unknown or the subject of inquiry. Glaucoma often

exists because of elevation of pressure in the eye, which may result in damage to the optic nerve.

However, glaucoma may also appear in patients with statistically normal intraocular pressure. This is one

example of the great complexity involved in diagnosis. In order to make an accurate diagnosis of

glaucoma, extensive evaluation and testing are necessary. This testing includes:

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Measurement of IOP with a tonometer.

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Evaluation of the condition of the optic nerve through ophthalmoscopy and SCODI testing.

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Examination of the angles of the eyes through slit lamp examination and gonioscopy.

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Measurement of the thickness of the central cornea with pachymetry.

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Evaluation of the extent of any peripheral vision loss by administration of a visual field

examination.

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Identification of other risk factors.

Once a physician has diagnosed glaucoma, it is possible to evaluate and initiate treatment options.

Because damage to the optic nerve usually results in irreversible vision loss, glaucoma therapy focuses

on preventing further loss of vision rather than restoring lost sight. Treatment is accomplished by lowering

intraocular pressure by means of medications, lasers, and/or surgery.

IOP is measured in millimeters of mercury. The average IOP in normal adults is 15 to 16 millimeters of

mercury. It has been determined statistically that pressures in excess of 21 will be evident in less than 2.5

percent of the normal population, and pressures over 24 millimeters of mercury will be found in less than

1 percent of non-glaucomatous individuals. For this reason, glaucoma is often suspected in patients

having IOP greater than 21 millimeters of mercury. With such patients, further diagnostic testing to either

rule in or rule out the glaucoma diagnosis may be recommended.

Quigley, HA, Broman, AT; British Journal of Ophthalmology March 2006; 90(3): 262-7

Thompson, Dennis; USA Today July 15, 2010

Basic and Clinical Science Course, Glaucoma, Section 10, American Academy of Ophthalmology, p. 3