The objective assessment of cataract is central to any epidemiological or therapeutic study of cataract. The objective methods consist of: 1: A resolution target projection ophthalmoscope (Acuity scope) for the estimation of potential visual acuity. 2: The Oxford Clinical Cataract Classification and Grading System, which records and quantifies the features of the lens that are visible at the slit-lamp microscope. This system is essential since photographic methods cannot define the morphology of cataract. 3: Two photographic methods; slit-lamp photography and retro-illumination photography are needed to give a comprehensive statement about the amount of cataract. The negatives are measured by computerised image analysis systems.