Quantifying amounts of visual field loss and setting target pressures

Optometric Management,  May 2000  by Litwak, Anthony B

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When attempting to set a target pressure for a patient, I'll look at the baseline intraocular pressure (IOP), the degree of glaucoma damage and the age of the patient. In general, I treat a younger glaucoma patient more aggressively because he has more time to become visually impaired.

I use the appearance of the optic nerve and a quantitative grading scheme based on three characteristics of the visual field to classify the glaucoma damage amount.

* Mean deviation. If this is between 0 and -6dB, vision loss is mild. Between -6 and -l2dB is moderate loss and greater than -l2dB is severe loss.

* The number of points on the pattern deviation plots. The 30-2 visual field has 76 points. If one quarter of the points are damaged (18 points show p-values of less than 5%), it's considered mild visual field loss. Between 18 and 36 points represents moderate loss, and more than 36 represents severe loss.

* The Four Numeric values just off fixation. Values greater than 20 decibels equal mild loss. Between 10 and 20 decibels indicate moderate loss; less than 10 decibels signals severe loss.

Set your target pressures according to the amount of damage: 20% to 30% reduction from the highest baseline IOP for mild loss, 30% to 40% for moderate loss and 40% to 50% for severe loss.

BY ANTHONY B. LITWAK, O.D.

Baltimore, Md.

Copyright Boucher Communications, Inc. May 2000
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