MEASUREMENT ERROR IN ASSESSING THE SIZE OF CORTICAL CATARACTS FROM RETROILLUMINATION PHOTOGRAPHS

This study describes a new method of quantifying anteriorly located co rtical cataracts using retroillumination photographs and computer plan imetry. Cortical cataracts were graded clinically and then photographe d using the Neitz retroillumination camera twice by each of 2 photogra phers. The cataract outlines were traced onto a transparent overlay, a nd computer planimetry was performed using a Scan Maker 600ZS, a MAC I I Computer and specially developed software. We estimated the measurem ent error of the method and its associated effect on sample size estim ates for clinical studies. We calculated that the variability in this technique would contribute about 21 additional subjects to overall sam ple size estimates in studies comparing the mean areas of cortical opa cities. In many studies this would be a small addition to total sample size requirements. This technique provides clinically useful measurem ents of the size of a cortical opacity as seen on a retroillumination photograph. This may be useful for future clinical studies on natural progression of cortical cataracts as well as for clinical trials of an ticataract drugs.