THE aetiology of myopia has been studied mainly by investigating the distribution of refractive errors in human populations1. No clear conclusion has emerged, however, so the prevailing clinical attitude is that myopia can neither be prevented nor cured, but only corrected with appropriate lenses. The mechanism of myopia can be rationally analysed only if a suitable animal model is found for this refractive condition. In the literature, there are only two examples of experimental myopia. Levinsohn2 claimed that a high degree of myopia develops in young monkeys when the body is kept elevated above the head for long periods of time; his results, however, have been questioned3,4. Young5 induced myopia by exposing monkeys to a restricted visual space, but the refractive error thus obtained was relatively small. During investigations on monocular visual deprivation in monkeys6 it was noted that the eye in which the lids had been closed by suture at birth developed a high degree of myopia. We report here a study of the effects of neonatal lid fusion on the refractive state and anatomy of the macaque monkey eye.