Evaluating the risk and progression of glaucoma: easier said than done

More prospective studies are needed to evaluate the role of diurnal and long-term intraocular pressure (IOP) function in glaucoma development and progression, according to Felipe A. Medeiros, MD, PhD, assistant professor of ophthalmology, University of California at San Diego, USA, speaking at the glaucoma subspecialty session.

While the 2002 Ocular Hypertension Treatment Study (OHTS) showed that each 1 mmHg increase in IOP was associated with a 10% increase in the risk of glaucoma development, it did not explore the effects of IOP fluctuation on risk. However, a 2004 report on the Advanced Glaucoma Intervention Study showed that each 1 mmHg increase in long-term IOP fluctuation increased the odds of progression by 30%.

Glaucoma progression can be diagnosed with visual fields, which may reveal a new defect or an enlargement or deepening of an existing defect, said Donald M. Budenz, MD, professor of ophthalmology, epidemiology and public health at Bascom Palmer Eye Institute, USA. New software for the Humphrey Field Analyzer II aids glaucoma progression analysis by adjusting for reduced hill of vision. It works with baseline full threshold or SITA fields and uses criteria from the Early Manifest Glaucoma Trial to judge progression at individual points. When using this software, it is important to pay attention to the baseline fields chosen, Dr Budenz said. The selection is automatic, but the clinician should review and sometimes change the selection.

He also cautioned against judging progression based on one test result showing a change, since the patient or technician may be having an off day that influences the outcome. Several retests will yield more accurate information about the likelihood of progression.

Optic disc photography is considered the gold standard for detecting glaucomatous change, but it has limitations such as slowness, subtlety, the need for many confirmatory tests and the need for expensive trials with large cohorts to provide validation, said David S. Greenfield, MD, professor of ophthalmology at the Bascom Palmer Eye Institute of the Palm Beaches, USA.

An expanding body of evidence shows that imaging devices also may be able to detect change and that some machines are more sensitive than expert observers looking at optic disc photographs, Dr Greenfield said. However, change detection strategies require prospective validation and statistical units of change probability are essential to differentiate test/retest repeatability from true biological change. In addition, the technologies with the highest discriminating power for diagnosing glaucoma may not necessarily be superior at detecting change.