Rapid off-response and retinal receptor diseases

A method was described to record the electroretinogram (ERG) in response to off- and on-stimuli, using Ganzfeld light stimulation. The rapid off-response representing the cone response was recorded with the off-stimuli with the light-dark ratio of 10:1 to maintain a constant photopic condition of 1.6 X 10(3) trolands (Zero log unit). The amplitude of the rapid off-response to completely extinguishing the background light was Vo and the amplitude elicited by intermediate intensities of off-stimuli was V. Vo-V was thought to represent the state of the receptor hyperpolarization, and it was correlated with the stimulus intensity (I) by Log (Vo-V) = nLog I + C; n averaged 0.84 +/- 0.15 in 12 normal subjects, and C was a constant. The scotopic b-wave was recorded by on-stimuli with the light-dark ratio of 1:100 and with the intensity less than -2.0 log units. The cone threshold was calculated using the criterion amplitude of the rapid off-response of 10 microvolts. The rod threshold was likewise computed with the criterion amplitude of the scotopic b-wave of 50 microvolts. The cone and rod sensitivities were determined in 5 patients with progressive cone (-rod) dystrophy and in 8 patients with central pigmentary retinal dystrophy. The cone sensitivity was markedly reduced in the former and the rod sensitivity was highly affected in the latter conditions. Separate evaluations of the cone and rod functions by the present technique will be clinically useful.