Classification of human senile cataractous change by the American Cooperative Cataract Research Group (CCRG) method: II. Staged simplification of cataract classification.

One thousand nine hundred and seventy-six cataracts extracted intracapsularly were classified according to the system adopted by the Cooperative Cataract Research Group (CCRG) Consortium. A nine-stage protocol for simplifying the classification data is presented. The method of simplifying the basic CCRG classification emphasizes anatomic similarities among lenses. Simplification is indicated when small numbers of cataracts in any class provide insufficient statistical power to allow detection of scientifically or clinically important differences in rates between comparison groups, if such differences exist; however, simplification unavoidably obscures the anatomic, biochemical, and biophysical features of individual cataracts. Age-specific characteristics of this population of 1976 cataracts are used to demonstrate the effects of the simplification process. The preponderance of mixed cataracts and the relative scarcity of pure cataracts are documented, and the implications of these numbers for cataract research are presented.