The attenuated PhNR and histopathology of the retina indicated that RGCs were markedly damaged, both functionally and morphologically in monkeys with ethambutol-induced optic neuropathy. These results implied that RGCs are predominantly affected in the retina of patients with ethambutol-induced optic neuropathy.

The results strongly suggest that voriconazole induces selective and reversible dysfunction of the retinal ON-bipolar cells in both the rod and cone pathways in monkeys. From the results obtained in monkeys in this study, it is suggested that the function of the retinal ON-bipolar cells was selectively and reversibly affected in voriconazole-treated humans who complained of transient visual disturbances.

PURPOSE. The purpose of this study was to investigate both functional and morphologic alteration of the retina acutely induced by N-methyl-N-nitrosourea (MNU) in monkeys.METHODS. The MNU was administered intravenously at a single dose of 40 mg/kg to six cynomolgus monkeys, and standard full-field electroretinograms (ERGs) were recorded 1, 3, and 7 days after dosing. In addition, the rod and cone a-waves in response to high-intensity flashes were analyzed by the a-wave fitting model (a-wave analysis). The photopic negative response (PhNR) was also recorded at the same time points. Furthermore, the retinas of two animals each were examined histopathologically 1, 3, or 7 days after dosing. RESULTS.The MNU attenuated all the standard full-field ERGs including the rod-driven and cone-driven responses; in the combined rod-cone response, the b-wave was more affected than the a-wave. In the a-wave analysis, the sensitivity parameters (S) of the rod and cone awaves had decreased on the day after dosing and remained unchanged thereafter. The maximum response parameter (R max ) of the rod a-wave gradually decreased. On the other hand, the R max in the cone a-wave transiently increased on the day after dosing and decreased thereafter; the PhNR amplitude showed a similar time course change. Histopathologically, the retinal lesion on the day after dosing mainly consisted of pyknosis and karyorrhexis in the photoreceptor nucleus. Depletion of some photoreceptor nuclei, and shortening and disorientation of the photoreceptor segments became prominent at 3 and 7 days after dosing. Localization of degenerated photoreceptors was consistent with that of rhodopsin-positive photoreceptors, resulting in a well-preserved central fovea. CONCLUSIONS.Our results indicated that MNU acutely induced rod-dominant photoreceptor degeneration in monkey retinas, but the photoreceptor function was impaired in both the rods and cones. Functional involvement of the postreceptoral components was also indicated.

Sildenafil produced reversible impairment of the rod and cone phototransduction in monkeys. Meanwhile, involvement of the postreceptoral retinal components was suggested. These findings contribute to the clarification of sildenafil-induced visual disturbances. It is suggested that the photoreceptors are predominantly, but not exclusively, affected in the retina of humans with sildenafil-induced visual disturbances.

The selectively reduced Rmax in the cone a-wave indicated dysfunction of the cone photoreceptors in digoxin-treated monkeys. Meanwhile, the enhanced and delayed rod response suggested alteration of retinal components other than the cone photoreceptors. These results may contribute to the understanding of digoxin-induced visual disturbances in humans. It is suggested that the cone function is markedly, but not exclusively, affected in the retina of such patients.