Risk Calculation Variability Over Time in Ocular Hypertensive Subjects

Abstract

To investigate the longitudinal variability of glaucoma risk calculation in ocular hypertensive (OHT) subjects. We reviewed the charts of untreated OHT patients followed in a glaucoma referral practice for a minimum of 60 months. Clinical variables collected at baseline and during follow-up included age, central corneal thickness (CCT), intraocular pressure (IOP), vertical cup-to-disc ratio (VCDR), and visual field pattern standard deviation (VFPSD). These were used to calculate the 5-year risk of conversion to primary open-angle glaucoma (POAG) at each follow-up visit using the Ocular Hypertension Treatment Study and European Glaucoma Prevention Study calculator (http://ohts.wustl.edu/risk/calculator.html). We also calculated the risk of POAG conversion based on the fluctuation of measured variables over time assuming the worst case scenarios (final age, highest PSD, lowest CCT, highest IOP, and highest VCDR) and best case scenarios (baseline age, lowest PSD, highest CCT, lowest IOP, and lowest VCDR) for each patient. Risk probabilities (%) were plotted against follow-up time to generate slopes of risk change over time. We included 27 untreated OHT patients (54 eyes) followed for a mean of 98.3±18.5 months. Seven individuals (25.9%) converted to POAG during follow-up. The mean 5-year risk of conversion for all patients in the study group ranged from 2.9% to 52.3% during follow-up. The mean slope of risk change over time was 0.37±0.81% increase/y. The mean slope for patients who reached a POAG endpoint was significantly greater than for those who did not (1.3±0.78 vs. 0.042±0.52%/y, P<0.01). In each patient, the mean risk of POAG conversion increased almost 10-fold when comparing the best case scenario with the worst case scenario (5.0% vs. 45.7%, P<0.01). The estimated 5-year risk of conversion to POAG among untreated OHT patients varies significantly during follow-up, with a trend toward increasing over time. Within the same individual, the estimated risk can vary almost 10-fold based on the variability of IOP, CCT, VCDR, and VFPSD. Therefore, a single risk calculation measurement may not be sufficient for accurate risk assessment, informed decision-making by patients, and physician treatment recommendations.