Quantitating nuclear opacification in color Scheimpflug photographs.

PURPOSE To test the validity of the color component subtraction method, a new objective technique of measuring nuclear cataract, and to correlate the tangent values of the different degrees of nuclear opacities to their corresponding subjective nuclear cataract grading using the Lens Opacities Classification System II and to another objective method of measuring nuclear cataract. METHODS Densitometries for red, green, and blue colors of the color Scheimpflug image were conducted simultaneously along the anteroposterior axis of the lens nucleus. The three color curves were subtracted from each other, giving rise to three subtracted curves: blue-red, green-blue, and red-green. This technique was applied to 99 color Scheimpflug photographs taken in 99 eyes of 51 patients with varying degrees of nuclear opacities. Using linear regression analysis, the regression coefficient obtained, called tangent value (TV), represents the degree of nuclear opacification. RESULTS Higher tangent value indicated greater nuclear opacification and was associated with higher correlation coefficient. This was seen graphically as an increased steepness in the slope of the subtracted curve. Good correlation existed between the subjective nuclear opacity grading and the objective tangent value. When the tangent values were correlated to the mean density of the three original color curves, good correlation was present in red and green, but only fair for blue, where maximum light scattering occurs. CONCLUSIONS These results support the validity of color component subtraction technique in measuring nuclear cataract. This technique provides quantitative measures of nuclear opacification, has good reproducibility, and is useful for monitoring nuclear cataract longitudinally.