Utilizing a high intensity photographic flash unit, electroretinograms were recorded from normal adults under fully light adapted conditions over a 5 log unit range of stimulus luminance (-1.35 to 3.34 log cd-s/m2). At lower luminance levels b-wave amplitude increased with increased luminance until it reached a maximum (Vmax of the Naka-Ruston equation) in agreement with previous work. At higher luminance levels, the b-wave amplitude decreased to 33% of Vmax and then plateaued. This previously unreported phenomenon has been named the photopic hill. There was no appreciable change in b-wave amplitude with increased interstimulus intervals from 15 sec to 5 min and luminance-response functions serially recorded for increasing and for decreasing stimulus luminance were very similar. These latter results indicate that the photopic hill is not due to light adaptation. The reason for the photopic hill and possible clinical implications are discussed.

No abstract

Dark-adapted electroretinograms were obtained over a 3.6-log range of stimulus intensities from 17 black and 15 white normal subjects. Subjects were grouped on the basis of light or dark fundus pigmentation, determined from digitized fundus photographs. B-wave amplitudes for each group were fitted by the Naka-Rushton equation, and the measures Vmax, log K, and n were determined. The luminance-response functions revealed that subjects with light fundi had larger b-wave amplitudes at all luminance levels. There was a significant difference between groups for Vmax and n but not for log K. A comparison of b-wave implicit times showed no significant difference between subjects with dark and light fundi. Ancillary tests and multiple regression analysis suggested that the relationship between Vmax and fundus pigmentation could not be attributed to age, gender, refractive error, axial length or intraocular pressure. The results have implications for the collection of normative electroretinographic data and for the interpretation of electroretinogram results.

Dark-adapted and light-adapted electroretinographic luminance-response functions were recorded from subjects with light or dark fundus pigmentation based on digitized fundus photographs. For dark- and light-adapted electroretinograms, subjects with dark fundi had smaller b-wave amplitudes at all luminance levels. There was no significant difference in b-wave implicit time for the dark-adapted electroretinogram, but there was a significant difference for the light-adapted ERG between the two groups. The results suggest that fundus pigmentation should be considered in the interpretation of electroretinogram results. A possible mechanism for the influence of fundus pigmentation on b-wave amplitude is based on increased resistance associated with melanin.

Normative dark-adapted electroretinograms were recorded simultaneously with a skin electrode and corneal electrode for varying stimulus intensities. The electroretinogram b-wave amplitudes for each electrode were fitted by the Naka-Rushton equation, and the parameters Vmax, K and n were evaluated. A comparison of parameters between the two electrodes showed a significant difference for Vmax and K but not for n. Vmax was approximately eight times smaller and K was 0.3 log unit smaller for the skin electrode than for the corneal electrode. B-wave amplitude and implicit time were also compared between the two electrodes. The b-wave amplitude ratio of the corneal electrode to that of the skin electrode increased with luminance and ranged from 1.83 to 7.68. Overall, b-wave implicit time for the skin electrode was approximately 10 ms shorter than that of the corneal electrode.