Glaucoma risk prediction model helps in managing ocular hypertension

The tool became available for use free of charge on the Internet (http://ohts.wustl.edu/risk/calculator.html) the afternoon of Dr. Kass' talk on Nov. 14. Created with data from untreated patients in the Ocular Hypertension Treatment Study (OHTS) and the European Glaucoma Prevention Study (EGPS), it uses five baseline features-patient age, IOP, central corneal thickness (CCT), vertical cup/disc (C/D) ratio by contour, and visual field pattern standard deviation (PSD)-to determine the risk that a patient with ocular hypertension will develop glaucoma over the next 5 years. Users can either input the patient's actual data to quantify risk or derive an estimate using a point system in which point values (0 to 4) are assigned to each risk factor, and the total is matched to a risk estimate.

There remains no one right answer on how to manage ocular hypertension, Dr. Kass stated, and individual clinicians need to decide for themselves whether the risk stratification model provides a reasonable approach. He cautioned clinicians using it to be aware that such models perform best for large population groups and do not guarantee accurate predictions for specific patients. The best performance is likely when applying the model to patients with features similar to those of the study groups used for its development and who are evaluated using the same testing protocols.

"However, the most important caution is that clinicians should consider this tool an aid to clinical judgment and not a replacement for it. There are a variety of factors, including age, health status, life expectancy, and patient preference, among many others, that should also be incorporated into the decision-making process," said Dr. Kass, OHTS study chairman and professor and chairman, department of ophthalmology and visual sciences, Washington University, St. Louis, MO.

Model construction

The risk stratification model using the pooled data from the OHTS and EGPS is an extension of work that began with OHTS. In 2002, the OHTS investigators published a risk model that identified age, vertical C/D ratio, IOP, CCT, and PSD as significant risk factors for glaucoma development. In addition, diabetes was found to be protective. However, that model needed to be confirmed in a large independent sample that included only untreated individuals. In addition, further investigation was needed to see how it performed in a population with a different demographic composition and whether the role of CCT as a newly identified risk factor could be corroborated, explained Dr. Kass.

"We were very fortunate that a large, independent sample was available to us through the EGPS population, that the EGPS shared enough protocol similarities with the OHTS that it could be used to test the OHTS prediction model, and yet that it was different enough to enable testing of its generalizability," he said.

The new model was constructed using data from 819 patients randomly assigned to observation in the OHTS and 500 placebo-treated patients in EGPS, of whom 165 went on to develop glaucoma in at least one eye. The OHTS prediction model was first tested by rerunning it using data only from the OHTS observation group (the original model was developed using data from all enrolled subjects) and then from the EGPS placebo group. In multivariate analysis, both tests identified age, vertical C/D ratio, IOP, CCT, and PSD as significant predictive factors, and with similar hazard ratios (HRs).