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Abstract
Seven young Maeaca nemestrina monkeys were placed in chairs under hoods, which restricted visual space to a distance of 20 inches or less, for a period of 1 year. In comparison with adult animals of similar characteristics in the same situation, the young monkeys did not demonstrate any effects of the situation for 4 or 5 months, whereas the adults began to show effects ivithin the first month. The young animals changed more rapidly once the effect became apparent and continued to change as long as they were in the situation; in contrast, the adults changed more sloiuly and leveled off at the end of 6 months toith no further changes. The amount of myopia developed by the young animals was 1 3/4 diopters against 3/4 for the adults in the same period. Three quarters of the adult animals developed myopia in excess of 1/2 diopters and 86 per cent of the young developed a similar amount. Significant age and sex differences in amount of myopia developed were found among the young monkeys. The effects of the situation on the young monkeys were similar to those found by Levinsohn, but not as marked.