Brightness acuity test and outdoor visual acuity in cataract patients.

The disparity between functional outdoor vision and the acuity measured in the standard refracting lane is well known among clinicians. A simple device, the brightness acuity tester (B.A.T.), was developed to predict a patient's functional outdoor acuity. The B.A.T. has an illuminated hemispheric bowl, 60 mm in diameter, with a 12-mm aperture. Fourteen normals and 50 patients with cataracts were tested using the B.A.T. and then tested outside in bright sunlight. The B.A.T. correlated extremely well (r = +0.84, P less than .0001) with the acuities measured outside. There was no decrease in visual acuity in the 14 normal patients, but there was a one to ten line decrease in vision among the cataract patients. Upon retesting, the B.A.T. scores did not vary, while outside testing scores did change due to variable outdoor ambient light levels on sunny days. The B.A.T. is a simple, repeatable, useful test for predicting functional outdoor acuity.