Polarising light biomicroscopy and the relation between visual acuity and cataract

The use of polarised light in biomicroscopy allows discrimination of lenticular features which are not discernible using standard biomicroscopic techniques. However, just as is true of most brightness-dependent photographic methods testing the effect of filters, past uses of polarised light did not involve any control of illumination. The present study involved the use of polarised light in the photo-biomicroscopy of the anterior segment in cataract patients, the consequential loss in illumination being mimicked with different neutral density filters. This served to distinguish between polarisation and attentuation. The patients were refracted and their corrected visual acuity was recorded. A qualitative scale was drawn up ranking weights of lenticular opacities. Spearman's rank correlation was applied to the photographs obtained with conventional and polarised-light biomicroscopy in turn. Brightness control served to confirm that biomicroscopy with polarised light offers some advantages over conventional methods, and correlates with visual acuity better than is true of conventional biomicroscopy. The Spearman ranks derived from the results obtained with polarised light correlate significantly with the patient's visual acuity. It is concluded that polarised light biomicroscopy, in conjunction with the standard examination, can improve the diagnosis of cataract and assist in relating it to a patient's visual acuity.