Assessing the reliability, discriminative ability, and validity of disability glare tests.

PURPOSE: To gather information regarding the reliability, discriminative ability, and validity of disability glare tests.
METHODS: The following glare tests were evaluated: the Miller-Nadler, Vistech MCT8000, Berkeley, van den Berg Straylightmeter, and the Brightness Acuity Tester used with the Pelli-Robson and Regan charts. Three test evaluation criteria were used: (1) repeatability--comparing test scores on two visits; (2) discriminative ability--the tests' ability to differentiate between young and old subjects and between old normal and cataract subjects; (3) validity--comparing cataract test scores with the reference standard of the van den Berg Straylightmeter. Three subject groups were evaluated: young normals (n = 24, mean age 24.3 +/- 3.3 yr), older normals (n = 22, mean age 66.0 +/- 6.2 yr), and early cataract (n = 33, mean age 70.6 +/- 8.1 yr). RESULTS AND
CONCLUSIONS: Data indicate that contrast sensitivity or low contrast acuity measured in the presence of glare are superior to disability glare scores in assessing cataract patients with normal neural function. Under glare conditions, contrast sensitivity and low contrast acuity scores from the Pelli-Robson, Regan, and Berkeley tests provide similarly reliable, discriminative, and valid measures of visual assessment in cataract. The Miller-Nadler glare tester poorly detects and measures subtle changes in the ocular media, such as early cataract, because of its large step sizes at low contrast thresholds. The poor reliability of the Vistech MCT8000 limits its usefulness. The study suggests that unless good chart design and psychophysics are used, the geometry and intensity of the glare source are of little importance.