The influence of refraction accuracy on automated perimetric threshold measurements

The effect of refraction accuracy on the differential light threshold of a Goldmann size III (0.43 degrees diameter) stimulus was evaluated in the right eyes of five normal subjects with randomly ordered sequence of plano, +1.00-, +2.00-, +3.00-, +4.00-, +5.00-, and +6.00-diopter (D) spherical overcorrections. Threshold measurements were performed at 0 degree, 5 degrees, 10 degrees, 15 degrees, 20 degrees, and 25 degrees eccentricity nasally along the 180 degrees meridian with the F4 program on the Octopus 201 perimeter. The +1.00- through +6.00-D overcorrections decreased the threshold values by an average of 1.4, 2.9, 4.2, 5.6, 6.7, and 7.6 dB, respectively, compared with the plano overcorrection. The depression of the differential light threshold was of similar magnitude at all eccentricities within the central 25 degrees.