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Junzo Kinoshita, Noriaki Iwata, Tomofumi Kimotsuki, Mitsuya Yasuda; Digoxin-Induced Reversible Dysfunction of the Cone Photoreceptors in Monkeys. Invest. Ophthalmol. Vis. Sci. 2014;55(2):881-892. doi: 10.1167/iovs.13-13296.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate functional alteration of the retina induced by digoxin in monkeys.
Digoxin was intravenously administered to cynomolgus monkeys and standard full-field electroretinograms (ERGs) were serially recorded. In other digoxin-treated monkeys, the rod and cone a-waves to high-intensity flashes were obtained and analyzed by the a-wave fitting model (a-wave analysis). The following responses were also recorded: dark- and light-adapted responses to flashes of different intensities (dark- and light-adapted luminance responses), photopic ERG elicited by long-duration stimulus (ON-OFF response), and the photopic negative response (PhNR).
Delayed b-wave was observed in all responses of the standard full-field ERGs; amplitude of the b-wave was increased in the rod response, but was decreased in the single-flash cone response and the 30-Hz flicker. These changes recovered gradually after elimination of digoxin from the blood. Digoxin enhanced and delayed the b-wave in the dark-adapted luminance-response analysis regardless of stimulus intensity. In the light-adapted luminance-response analysis, digoxin attenuated the a- and b-waves only at high and middle stimulus intensity, respectively. The a-wave analysis revealed selective decrease in the maximum response parameter (Rmax ) in the cone a-wave. Both the b- and d-waves of the ON-OFF response were delayed.
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.
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