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ESSENTIALS OF DIAGNOSIS
Three types of chronic glaucoma: open-angle glaucoma, angle-closure glaucoma, and normal-tension glaucoma.
No symptoms in early stages.
Insidious progressive bilateral loss of peripheral vision, resulting in tunnel vision; visual acuities preserved until advanced disease.
Pathologic cupping of the optic disks.
Intraocular pressure is usually elevated.
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GENERAL CONSIDERATIONS
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Chronic glaucoma is characterized by gradually progressive excavation (“cupping”) (eFigure 7–31) (eFigure 7–32) of the optic disk with loss of vision progressing from slight visual field loss to complete blindness. In chronic open-angle glaucoma, primary or secondary, intraocular pressure is elevated due to reduced drainage of aqueous fluid through the trabecular meshwork. In chronic angle-closure glaucoma, which is particularly common in Inuits and eastern Asians, flow of aqueous fluid into the anterior chamber angle is obstructed. In normal-tension glaucoma, intraocular pressure is not elevated but the same pattern of optic nerve damage occurs.
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Primary chronic open-angle glaucoma is usually bilateral. There is an increased prevalence in first-degree relatives of affected individuals and in diabetic patients. In Afro-Caribbean and African persons, and probably in Hispanic persons, it is more frequent, occurs at an earlier age, and results in more severe optic nerve damage. Secondary chronic open-angle glaucoma may result from ocular disease, eg, pigment dispersion, pseudoexfoliation, uveitis, or trauma; or corticosteroid therapy, whether it is intraocular, topical, inhaled, intranasal, or systemic.
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In the United States, it is estimated that 2% of people over 40 years of age have glaucoma, affecting over 2.5 million individuals. At least 25% of cases are undetected. Over 90% of cases are of the open-angle type. Worldwide, about 45 million people have open-angle glaucoma, of whom about 4.5 million are bilaterally blind. About 4 million people, of whom approximately 50% live in China, are bilaterally blind from chronic angle-closure glaucoma.
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Because initially there are no symptoms, chronic glaucoma is often first suspected at a routine eye test. Diagnosis requires consistent and reproducible abnormalities in at least two of three parameters—optic disk or retinal nerve fiber layer (or both), visual field, and intraocular pressure.
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1. Optic disk cupping
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Optic disk cupping is identified as an absolute increase or an asymmetry between the two eyes of the ratio of the diameter of the optic cup to the diameter of the whole optic disk (cup-disk ratio) (eFigure 7–31) (eFigure 7–32). (Cup-disk ratio greater than 0.5 or asymmetry between eyes of 0.2 ...