In each of five monkeys, one eye was fitted with a diffuser lens at birth. This lens allowed pattern vision, but also reduced contrast by about 1 log unit. In four out of five monkeys, the treated eyes were shorter and more hyperopic than the untreated fellow eyes. At 25 weeks of age, interocular differences (OD -- OS) of the experimental group were significantly greater than interocular differences of age-matched normal monkeys for both axial length (P < 0.05) and refractive error (P < 0.02). In addition, while the treated eyes were significantly different from normal eyes for both axial length measurements (P < 0.01) and refractive error (P < 0.01), there were no significant differences between the untreated fellow eyes and normal eyes. In primates less severe pattern deprivation appears to produce an effect on eye growth that is opposite to that of severe pattern deprivation (little or no pattern vision), which typically results in axial myopia.