Sources of variability in the clinical photostress test

The photostress test is a simple clinical technique that can differentiate between retinal and postretinal disease. Unfortunately a wide range of normal results have been reported in the literature and it is perhaps for this reason that the test has been little used by clinicians. The purpose of this investigation was to evaluate the effect of photostress technique, age, ametropia, pupil size and acuity on photostress recovery time (PSRT) in normal subjects. Photostress recovery time was measured in 50 healthy subjects whose ages ranged from 21 to 69 using three clinically applicable techniques and a reference technique designed to bleach a consistent amount of photopigment. The agreement between each clinical technique and the reference technique was determined. Mean photostress recovery time differed for each of the techniques studied. Analysis of the data obtained with the reference and the best clinical technique showed that age was the only factor that had a significant effect on PSRT. The best clinical technique involves exposing the eye to the light from the direct ophthalmoscope for 30 s and measuring the time taken for acuity to return to within one line of pre-bleach acuity. Photostress recovery time increases with age but is independent of pupil size, ametropia and visual acuity.