CHANGES IN EYE GROWTH PRODUCED BY DRUGS WHICH AFFECT RETINAL ON OR OFF RESPONSES TO LIGHT

The interaction between drugs which affect ON and OFF responses to lig ht and ocular growth was investigated in 154 eyes of newly-hatched chi cks raised with normal vision or monocular occlusion with regular intr avitreal injections of APB (2-amino-4 phosphonobutyric acid) or PDA (c is 2,3-piperidine-dicarboxylic acid). The experimental results indicat e that APE, at a dose sufficient to abolish the b-wave of the electror etinogram (but not to show extensive damage to the retinal neurons at the light microscopic level), caused a significant decrease in the axi al growth of the eyes when compared with normal eyes. APB did not resu lt in a significant difference in the growth rates of the occluded eye s compared with occluded controls. By contrast, injection of PDA into occluded eyes at a dose which reduced the response at light offset in the electroretinogram (and also affected the ON-response), caused a dr amatic reduction in elongation of those eyes compared with occluded co ntrols. Injection of PDA into eyes raised in a normal visual environme nt did not induce a significant difference from the growth rate of nor mally reared control eyes. These growth changes support the hypothesis that drugs which affect the physiological function of the retina, in particular, the strength of the ON and OFF responses, interact with th e visual rearing environment to cause a consistent pattern of changes to eye growth and refractive error.