Purpose: To propose a general conversion approximation algorithm and illustrate its application to two cataract classification systems, the Lens Opacity Classification System III (LOCS III) and Wisconsin Cataract Grading System (Wisconsin system).
Methods: Lens opacity of 3265 participants (78.7% response rate) aged 40 to 80 years from the Singapore Malay Eye study were assessed both clinically during slit-lamp examination using LOCS III, and via slit-lamp and retro-illumination photographic grading using the Wisconsin system. Collapsed contingency tables were used to convert between the LOCS III and Wisconsin System.
Results: The conversion between the two cataract classification systems is affected by the direction of transformation. The conversion algorithm was validated and explained with an application example.
Conclusions: An approximate conversion algorithm for any two cataract grading systems was proposed and applied to the LOCS III and Wisconsin system. These findings provide general ways to pool and compare cataract prevalence using different grading systems in epidemiological studies.