Konrad Pesudovs, BSc Optom, Douglas J Coster, FRACO, Department of Ophthalmology,
Flinders Medical Centre, Bedford Park, South Australia, Australia.

Purpose. The relationship between measures of visual function and level of cataract was explored to determine what differences exist for morphological subgroups, what additional information different tests of visual fuction provide and whether visual function could be predicted on the basis of cataract score.

Method. 310 eyes of 173 patients were assessed. The measures of visual function employed were high contrast visual acuity (VA), low contrast (25%) visual acuity (LCVA), LCVA under glare conditions (LCVA glare), Pelli-Robson contrast sensitivity (PRCS), PRCS under glare conditions (PRCS glare) and spatial contrast sensitivity at 2, 3.7, 7.5 and 15 c/d (CS2, CS3.7, CS7.5, CS15). Cataract was graded according to the LOCS III grading system. From these scores the cataracts were categorised into pure and mixed morphological groups.

Results. Each morphological grouping exhibits a different pattern of visual dysfunction. The relationships between the measures of visual function and each LOCS III grade of cataract have been elucidated. Posterior subcapsular cataract was not associated with visual acuity, but was associated with PRCS glare (P<0.01) and LCVA glare (P<0.01). Cortical cataract was poorly correlated with all measures, including glare measures. If we rescored the cortical cataract on the same scale but to include opacities only within the pupillary zone, then the correlations with all measures of visual function improved, with LCVA glare (P<0.01) and PRCS (P<0.01) being most significant. Nuclear cataract was not correlated with glare measures, or VA, but was associated with PRCS (P<0.01).

Conclusions. Visual acuity is a poor indicator of visual function in cataract. The establishment of relationships between LOCS III cataract score and the various measures of visual function provide expected values of visual function for all levels of cataract formation. These standards facilitate determination of the contribution of cataract to visual dysfunction in cases of comorbidity and age-related macular degeneration. This should improve the predicted outcome of surgery.