Myopia in the lid-sutured tree shrew (Tupaia glis).

Myopia in the lid-sutured tree shrew (Tupoia g/is) Many mammals reared with visual deprivation display abnormally poor visual behavior while using their deprived eyes1-4,9,1°. These results typically have been attributed to defective development of the central visual pathways during the deprivation 6 s,11,13. However. it is important to consider non-neural (e.g., optical) sources which might contribute to their poor visual capacities. For example, Wiesel and Raviola 14 report that monkeys reared with lid suture exhibit considerable myopia in the deprived eye. In the course of other studies of lid-sutured tree shrews, we discovered that the deprived eye was consistently and considerably myopic with respect to either the open eye or the eyes of normally reared tree shrews. Our data are from I I tree shrews (Tupaia glis) raised with the lids of one (9 animals) or both (2 animals) eyes sutured shut. The lids were sutured after trimming the lid margins during the 7th postnatal day (eye opening normally occurs on about day 20). They were maintained in this fashion until other terminal experiments In adulthood (4-36 months of age). In addition to the lid-sutured tree shrews, t 5 normally reared adults served as controls. The animals were prepared for electrophysiological recording using our previously described methods t2. These included initial anesthesia with hatothane followed by N20-Oz (70:30), topical placement of atropine into the eyes, paralysis, artificial ventilation, and placement in a stereotaxic head holder. Retinoscopy. Carefully calibrated contact lenses were placed on the corneas, and streak retinoscopy was performed. The lenses were replaced as needed until both eyes were deemedemmetr°pic(i'e'" after thec°rrecti°n suggested bY Glickstein and Millodot~: also see our previous discussion of this point~2). At least two different observers evaluated the retinoscopy with no substantive discrepancy (i.e., always-I diopter). In the 15 normally reared tree shrews, we found that the eyes required contact lenses of 99.2 ~: 3.2 diopters (mean T S.D.) to achieve emmetropia, and the average interocular difference was 0.5 i 1.5 diopters. Table I expresses these values for the lid-sutured tree shrews. For each of the monocularly sutured animals, the deprived eye required much less (15-28 diopters) power to achieve proper focus. This presumably indicates myopia in the deprived eyes since the values for the non-deprived eyes were in the normal range. In two of the animals (Nos. 175 and 178), retinoscopy was quickly performed after