Figure 5.

Bleaching of photoreceptors, using the 488-nm illumination with laser power of 260 μW through the pupil. The test started with a 30-second exposure using the 20° field (images not recorded). The irradiated area was then 20° × 30°, or 0.53 cm², and the retinal irradiance was 490 μW/cm². The rods in the 20° high strip were then bleached to 99%; no changes in AF were detected in the subsequent images. (A) A 30° fundus image was taken immediately after the field was switched to 30° × 30° (0.79 cm²).The retinal irradiance was then 330 μW/cm². The superior and inferior fundus was then roughly dark adapted. Images were recorded after 11, 21, 31, and 51 seconds, to document the effect of bleaching. (B) Image recorded 30 seconds after image (A). No clear differential AF was detected between the areas that were and were not initially bleached. (C) Time course of the attenuation of the AF during bleaching for three subjects (age range, 23–47years). Error bars are SD, calculated from propagation of errors. Measurements were made within the superior (▵) and inferior (▿) dark bands, at the boundary of the dark area (eccentricities, 12°–17°), and in the fovea (○). The AF measured in the bleached zone outside the fovea acted as the reference. The data were fitted by exponential functions. At t = 0 the attenuations ranged from 1.37 to 1.47, corresponding to optical densities of 0.16 to 0.19 DU for the rods (500 nm). The attenuation was reduced to 1.05 (5% absorption) after a bleaching duration of 12 to 17 seconds and to 1.02 (2% absorption) after 17 to 24 seconds. Marginal increases in AF were observed at the fovea for RL and TM (○), perhaps related to regeneration of the photopigment.