While high IOP has been a standard marker for diagnosing primary open-angle glaucoma, it is not foolproof. Patients with high IOP do not necessarily progress to glaucoma, while some patients with low or normal pressures do develop the disease. To improve the accuracy of diagnosis and better estimate progression, clinicians need to take into account other information, such as IOP fluctuation, visual field analysis with new technology, and data obtained with the latest imaging devices.
While the OHTS study showed that each 1 mm Hg 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 mm Hg increase in long-term IOP fluctuation increased the odds of progression by 30%.
"We need more prospective studies to evaluate the role of diurnal and long-term IOP fluctuation in glaucoma development and progression. What we have so far are studies that have not been directly designed to evaluate fluctuations," Dr. Medeiros said. "And we need to also search for better methods to evaluate and estimate IOP fluctuations."
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, MPH, professor of ophthalmology, epidemiology, and public health at Bascom Palmer Eye Institute. 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, Palm Beach Gardens, FL.
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.
The program was jointly sponsored by the New York Eye and Ear Infirmary, which received a financial benefit from Pfizer Ophthalmics, and by CME2, an independent subsidiary of Advanstar Communications, publisher of Ophthalmology Times.