The age-related eye disease study (AREDS) system for classifying cataracts from photographs: AREDS report no. 4

PURPOSE: To describe the system for grading cataracts from photographs in the Age-Related Eye Disease Study (AREDS). METHODS: The system for grading cataracts in AREDS uses photographs taken in a standardized fashion with specially modified cameras at 11 clinical centers. The photographs are evaluated by graders for quality and cataract severity at a central reading center. The area of lens involvement is used to assess the severity of cortical and posterior subcapsular opacities. Optical density of nuclear opacity is graded against a series of seven standard photographs. Contemporaneous variability in grading is evaluated periodically by having a second examiner regrade a subset of the photographs. Temporal variability is assessed by annually regrading a subset of photographs. RESULTS: Photographs of 925 eyes, most with no or early lens opacities, were regraded to assess intergrader reliability. For cortical opacities, there was an absolute difference of 10% or greater of area involved in 1.9% of the replicate gradings. For posterior subcapsular opacities an absolute difference of 5% of area involved was noted in 2.8% of the regraded photographs. For nuclear opacities, absolute differences of 1.5 or more steps were observed in 0.6% of eyes. There was little evidence of temporal drift in grading any of the three types of opacity during four annual regrades. CONCLUSIONS: We have demonstrated a high degree of reliability in grading the severity of lens opacities in a large study cohort with mostly early lens changes, the type of cohort most likely to be entered in clinical trials involving cataract prevention. The Age-Related Eye Disease Study System for Classifying Cataracts From Photographs could be useful in studies where there is a need to standardize data collection over time and across different data collection sites. Limitations of the system include the cost of implementation and, currently, the limited amount of data on grading reproducibility for more advanced lens opacities.