Knowledge of glaucoma risk comes with time

"Despite the recent advances in diagnostics and therapeutics, management of glaucoma still remains more of an art than a science," said Dr. Singh, professor of ophthalmology and director glaucoma service, Stanford University School of Medicine, Stanford, CA.

He explained that advances in risk assessment for ocular hypertension derive largely from data collected in the Ocular Hypertension Treatment Study (OHTS). That trial was designed to investigate the benefit of IOP-lowering therapy in patients with elevated IOP but normal optic nerves and visual fields.

"When it comes to visual fields and optic nerve findings, however, it is important to keep in mind that these features define the disease. Purists might say that many individuals who had optic nerve or visual field abnormalities predictive of glaucoma in addition to elevated IOP may already have glaucoma and therefore would be more likely to show progression along the continuum of glaucomatous disease relative to those who truly had normal optic nerves and visual fields," Dr. Singh said.

Diabetes, surprisingly, was found to be protective against glaucoma development in OHTS, although its role in decreasing risk has not been confirmed in other studies.

The finding that family history of disease did not correlate with progression was unexpected and may relate to the self-reporting method of assessment, he said. "Perhaps use of a more accurate method of determining family history might have given a different result."

Race, male gender, and heart disease were significantly associated with progression in univariate analysis. These features, however, were not found to be independent predictors of risk in the multivariate analysis.

Based on the OHTS findings, several risk calculators for ocular hypertension progressing to glaucoma have been developed. One described by Felipe A. Medeiros, MD, and colleagues at the University of California, San Diego, has been validated and published recently [Medeiros FA, et al. Arch Ophthalmol 2005;123:1351-1360]. Their risk calculator is now available both as a slide rule and a pocket-sized electronic calculator.

Patient counseling

Although there have been several large clinical trials evaluating the effects of different interventions on the progression of established glaucoma, these studies have not provided information pertaining to risk, which is comparable to that obtained from OHTS. Such failure to provide useful information may relate to the fact that it generally takes many years for most patients with early disease to have progression to severe visual impairment, and longitudinal studies that follow patients for substantial periods are lacking.

However, some data on rate of progression to blindness in untreated persons with glaucoma or suspected glaucoma are available from a cohort study conducted in St. Lucia, West Indies. Using criteria from the Advanced Glaucoma Intervention Study, the West Indian study found that after 10 years, the cumulative probability of reaching end-stage disease in at least one eye was about 16% and was about 10% for bilateral end-stage disease.

"Those rates are relatively high, but it is important to keep in mind that the West Indian population consisted of blacks with predominantly West African ancestry," Dr. Singh said.