Basics of Glaucoma

Basics of Glaucoma

When a patient with elevated pressure is thoroughly evaluated and found to have no evidence of optic

nerve damage or visual field loss, the physician may diagnose ocular hypertension, or glaucoma. Patients

in this category are usually those with pressures in the low- to mid-20s, but occasionally higher. These

patients either may develop glaucomatous damage over the next months to years, or may never develop

damage at all. Eye physicians may decide to treat an ocular hypertension patient on the basis of age,

medical history, family history of glaucoma, or condition of the fellow eye, rather than wait for evidence of

optic nerve damage or visual field changes.

Additionally, doctors may suspect glaucoma if the patient’s optic nerves are either abnormal in

appearance or are not mirror images. The optic nerve is housed within the optic disc. As IOP increases

and presses on the optic nerve, the area of the “cupping” can increase in size. The amount of “cupping” is

described by the cup-to-disc (CD) ratio, which ranges from 0.0 to 1.0. A larger CD describes a greater

amount of cupping of the disc, increasing the possibility of glaucomatous damage. If the patient’s optic

discs are unequal in appearance, the physician might suspect glaucoma secondary to optic nerve

asymmetry.

Abnormal Cupping Normal Cup-Disc-Ratio

Frequently, a pachymeter will measure the corneal thickness of glaucoma suspects to determine if the

cornea is thicker or thinner than average. Ocular hypertensive patients with thicker-than-normal corneas

develop glaucoma much less frequently than patients with thin, or even normal, corneas, provided that all

other factors (age, IOP level, cup size, etc.) are equal. Average corneal thickness is 0.535 to 0.565

millimeters (or 535 to 565 microns). Applanation tonometry of an unusually thin cornea can result in a

false reading that is lower than the actual IOP because the resistance of the corneal tissue is less than

expected. Additionally, a thick cornea will give a false high applanation reading because the resistance of

the corneal tissue is greater than expected. Modern thought seems to indicate the thinner-than-average

cornea might indicate a more vulnerable optic nerve.

RISK FACTORS OF GLAUCOMA

There are several demographic and health trends that have increased the number of people at risk of

glaucoma. In addition to genetic risk factors among immediate family members, according to the

Glaucoma Research Foundation,

other risk factors include:

•

Age:

Adults older than 60 are six times more likely to develop glaucoma than their younger

counterparts. As the number of older Americans grows, so does the number of glaucoma

patients.

•

Race:

The risk of glaucoma is six to eight times greater among African-Americans than

Caucasians; Hispanics run a higher risk than people of European descent; Asians represent a

significant percentage of patients with angle-closure glaucoma.

•

Obesity and diabetes:

Diabetic patients are twice as likely to develop glaucoma as people

without the disease. As diabetes and obesity reach epidemic proportions, the number of

glaucoma cases is expected to increase, as well.