Rhesus monkeys were visually deprived unilaterally by surgical closure of the eyelids at different ages after birth. The animals were subsequently conditioned to respond to Landolt rings in different positions to determine visual acuity. After acuity thresholds were established for the nondeprived eye, it was surgically closed; the deprived eye was opened, and the acuity of the deprived eye was measured. The results reveal that severe visual impairment without recovery was caused by lid closure during the first four weeks of life. If lid closure was performed at three months or afterwards, the deprived eye showed rapid functional recovery when the lids were reopened. The electroretinograms in two monkeys with stimulus deprivation amblyopia were normal.
von Noorden GK, Dowling JE, Ferguson DC. Experimental Amblyopia in MonkeysI. Behavioral Studies of Stimulus Deprivation Amblyopia. Arch Ophthalmol. 1970;84(2):206-214. doi:10.1001/archopht.1970.00990040208014