Early visual deprivation results in persistent strabismus and nystagmus in monkeys

To understand to what extent visual-pattern deprivation during infancy results in strabismus and nystagmus, the authors examined the long-term consequences of this type of deprivation in monkeys during the first 50 days of life. Three cynomolgus and three rhesus monkeys had the eyelids sutured closed within 24 hr of birth. At 25 days of age, the eyelids were opened, and the eyelids of the fellow eye were sutured closed for an additional 25 days (reverse-eyelid suture). When the eyelids were opened at 50 days of age, each monkey was found to have 20-30 delta of exotropia and nystagmus, which persisted for the duration of the study (1 yr). The cynomolgus monkeys developed a monocular 8-10 Hz pendular nystagmus in the eye sutured first. The rhesus monkeys developed a conjugate nystagmus with both jerk and pendular components. The slow phases often had velocity-increasing profiles. The rhesus monkeys also had a superimposed latent component to the nystagmus found during monocular viewing. One additional rhesus monkey was examined after 55 days of binocular-eyelid suturing. This monkey also developed exotropia and nystagmus resembling that of the other rhesus monkeys. These findings suggest that early pattern vision in monkeys is necessary for the development of normal ocular alignment and gaze-holding ability.