Retinal toxicity in albino rabbits induced by intravitreal injection of strophanthin-K

Time course and extent of strophanthin-K induced disturbances of flash electroretinogram (F-ERG) has been observed in 12 albino rabbits treated by a single dose of 1, 3 and 9 ug/0.1 ml of intravitreal injection. A phenomenon of the dependence of a- and b-wave amplitude changes on dosage was demonstrated. A 9 ug/0.1 ml dose caused a flat a- and b-wave showing the F-ERG wave could be completely suppressed by larger dose of strophanthin-K. Two parameters of "attenuation kinetics" are proposed to identify the pharmacodynamics and toxic kinetics on retina as time profile is concerned: 1) B (the slope of attenuation curve); 2) Et1/2 (half attenuative time). B and Et1/2 are helpful in making a tentative identification of the target cells on retina and in demonstrating a synergism or antagonism between drugs if any. The a-wave of F-ERG, having a steeper slope, is more sensitive than b-wave in terms of strophanthin-K toxicity bringing forth a quantitative criterion in visual pharmacology. The attenuation of amplitude in a-wave may therefore be considered as an early response to this drug. The direct pupillary response test were also done pre- and post-strophanthin-K, and the results of this test support that of F-ERG.