The morphology of cataract and visual performance.

The various effects of cataract on vision are reviewed. The morphological types of senile cataract are classified into three basic categories: cortical spoke, nuclear and posterior subcapsular (PSC). The significant basic effect of cataract on the optical system of the eye is that of light scattering. Forward light scattering (light scattered towards the retina) accounts for reduced contrast sensitivity, for glare and for reduced visual acuity. Other effects of cataract are a myopic shift, a possible astigmatism change, monocular diplopia and polyopia, colour vision shift, reduced light transmission, and field of vision reduction. The effect of the various cataract morphologies on these functions is discussed. The nature of the effect varies with the degree of the cataract and with the cataract morphology. The assessment of a patient's visual disability is therefore not a simple task and cannot be based solely on the visual acuity nor on the objective measurement of the cataract.