Electroretinographic changes in aged pigeons

Photopic electroretinograms, either to full-field light flashes (FERGs) or to contrast-reversal of square-wave gratings (PERGs) have been recorded in pigeons aged 2 years old (n = 5) and 10 years old (n = 5). Mydriatic pupil diameter, ophthalmoscopic appearance of the retinal fundus and optic media, and refractive state were comparable in the two groups. V/log I functions of individual FERG components (a-wave, b-wave and oscillatory potentials) displayed significantly lower slopes in the old birds than in the young, which suggests a reduction in retinal gain. PERG amplitude also was significantly lower in the older birds over a wide range of spatial frequencies (0.2-8.8 c/deg). Estimated visual acuity based on the extrapolated high-frequency cut off was 18 c/deg in the younger birds and 7.8 c/deg in the older birds. These results are in agreement with psychophysical data and retinal age-related losses in visual acuity, photoreceptors and retinal ganglion cells. Since these findings are comparable to those reported for humans, the results suggest that pigeons may serve as a useful model for human visual aging.