THE EFFECTS OF BLOCKADE OF RETINAL CELL-ACTION POTENTIALS ON OCULAR GROWTH, EMMETROPIZATION AND FORM DEPRIVATION MYOPIA IN YOUNG CHICKS

To investigate the influence of brain mediated functions on control of ocular growth, young chicks were treated monocularly with intravitrea lly injected tetrodotoxin (TTX) to block retinal ganglion cell action potentials. TTX injections (0.7 mu g in 7 mu l) were given on day 6 af ter hatching in both binocularly open and monocularly deprived chicks. Injections were repeated every 48 hr for a period of 8 days (TTX-open ; TTX-MD). Control groups of animals received intravitreally injected phosphate buffered saline (PBS-open; PBS-MD) to one eye on the same sc hedule. There was a minimum of eight animals in each group, Recovery f rom form-deprivation myopia during blockade of retinal cell action pot entials was also investigated. Results demonstrate that blockade of re tinal cell action potentials by TTX produces reduced growth of the ant erior segment of the eye and crystalline lens in both binocularly open and MD chicks. Blockade of retinal cell action potentials does not pr event form-deprivation induced vitreous chamber elongation and myopia. Form deprived myopic eyes were found to emmetropize despite blockade of retinal ganglion cell action potentials giving further evidence for local ocular control of emmetropization. Blockade of retinal ganglion cell action potentials did not prevent changes in choroidal thickness in eyes developing axial myopia or eyes recovering from induced myopi a.