In order to investigate the changes in the scotopic and photopic ERG induced by the administrations of retino-toxic agents, 30mg/kg of body weight of sodium iodate and sodium iodoacetate were given in albino rabbits intravenously. Animals were anesthetized with intra venous urethane injection (1.5g/kg) and the pupils were dilated with atropine. The eye was stimulated with a single light flash (800 lux at the animals eye) of 200 msec duration. Prior to the recording of the scotopic ERG, animals were preadapted to light of 150 lux for 30 minutes.
During dark adaptation, b-potential increased rapidly for the first 6-8 minutes followed by slow augmentation in normal eye. On the cessation of dark adaptation, b-potential dropped immediately, its decrease a-mounting up to 80% of the maximal potential attained during dark adaptation.
By the administration of sodium iodate, c-wave disappeared immediately accompanied by apparent increase in the slow cornea-negative potential. No changes were noted in the b-potential during the first hour after iodate. Slow recovery phase during dark adaptation disappeared. Thereafter, b-potential diminished progressively with deepening of the slow negative wave. In some cases, b-wave almost extinguished 3 hours after iodate, and in another cases, some recovery of the b-wave was noted 48 hours after iodate administration.
Iodoacetate produced immediate fall of b-potential with slow decrease of negative potential which progressed to the complete disappearance of the whole ERG responses. In some cases, b-wave reappeared 5 hours after iodoacetate, with prolongation of its duration. At 24-48 hours after the administration, no electrical response, to light stimulus was elicited. From the obtained ERG findings, it can be deduced that the functions of the pigment epithelium could be disturbed secondary to the degenerations of visual cells.
No correlation could be demonstrated between the ERG changes and the EOG changes after administration the toxic agents.
Histological examinations of eyes at various intervals after administrations of retinotoxic agents revealed the degeneration of the pigment epithelium, sensory organelles of the visual cells and inflammatory changes in the choroid by iodate; and destruction of visual cells with preservations of the pigment epithelium by iodoacetate.
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