We found that refractive errors were present in about 80% of 650 mentally retarded infants and children. The appropriate spectacles were prescribed for 75%. Evaluation of the effectiveness of wearing spectacles was based on the observation of their daily behavior and visually evoked cortical potentials to pattern stimuli (PVECP). Despite difficulties, we are able to record PVECPs in 160 subjects, of whom PVECPs were detectable in 140 (87.5%). The amplitudes of PVECPs with spectacles were larger than those without spectacles in 55.2% of the 105 subjects whose PVECPs were examined both with and without spectacles.