Optometrists have long known that ocular hypertension is a risk factor for development of primary open-angle glaucoma (POAG), but anticipating disease manifestation is a perennial problem for doctors monitoring such cases. In a recent study, researchers determined the cumulative incidence and severity of POAG after 20 years of follow-up among participants in the Ocular Hypertension Treatment Study (OHTS). The data from this long-term follow-up can be used to inform the management of patients with ocular hypertension.
In phase one of the seminal study, participants were randomized to receive either topical ocular hypotensive therapy (medication group) or close observation (observation group). In phase two, both groups received medication. In phase three, participants received eye exams and visual function assessments.
Over 1,600 individuals were randomized in phase one of the trial. Of those, 483 participants (29.5%) developed POAG in one or both eyes (unadjusted incidence). After adjusting for exposure time, the 20-year cumulative incidence of POAG in one or both eyes was 45.6% among all participants, 49.3% among participants in the observation group and 41.9% among participants in the medication group. The 20-year cumulative incidence of POAG was 55.2% among African-American participants and 42.7% among participants of other races, but the authors noted “when patients are stratified by baseline risk, Black/African American individuals and others in the same risk category have similar outcomes.”
“In total, 199 participants developed optic disc POAG deterioration in one or both eyes without visual field abnormality based on study criteria,” the authors noted in their study. “As a group, these participants had few differences from participants who did not develop POAG when comparing the last assessed visual field MD or visual field PSD, visual acuity, contrast sensitivity or foveal sensitivity. Greater functional differences might have been detected with more rigorous psychophysical, performance or electrophysiologic tests that were not performed in the OHTS.”
Over the course of the study, 515 participants died, which alarmed the authors. “It is concerning that the number of participants who died and the number who developed POAG were approximately the same during the OHTS,” they noted in their study. “The incidence of POAG appeared to be generally linear over 20 years, with a possible modest increase in the rate of conversion after 15 years. We cannot determine whether this increase was a true change associated with increasing age or whether it was associated with missing data from loss to follow-up and death.”
The authors noted some factors that may have implicated the results. For example, participants in the OHTS may have a lower risk of developing POAG because volunteers in most studies may be more likely to return for follow-up visits and adhere to medication.
“In addition, the OHTS used strict criteria for conversion to POAG. If other diagnostic criteria, such as OCT results, had been included or if less stringent reproducibility criteria had been used, a higher incidence of POAG would have been observed,” the authors concluded.
Kass MA, Keuer DK, Higginbotham, EJ, et al. Assessment of cumulative incidence and severity of primary open-angle glaucoma among participants in the ocular hypertension treatment study after 20 years of follow-up. JAMA Ophthalmology. Epub ahead of print.