LL BEHAVIORAL-STUDY OF REFRACTION, CORNEAL CURVATURE, AND ACCOMMODATION IN RAPTOR EYES

Since there is much speculation in the literature regarding the accomm odative abilities of raptors. we undertook a behavioral study of accom modation in the five families of raptors. The resting refractive state and amplitude of accommodation were measured using infrared video pho torefraction in a variety of wild-caught and captive-bred raptors. The resting corneal curvature and the extent of changes in corneal curvat ure during accommodation (corneal accommodation) were measured using v ideo keratometry. External ocular and head dimensions were measured wi th calipers to look for correlates with accommodative amplitude. In ge neral, all eyes examined were of high optical quality and relatively f ree of aberrations. No significant refractive errors were recorded in any of the birds examined (< 1.0 diopters (D)). In general, significan t amplitudes of accommodation were measured in the hawks (up to 25.0 D ), but little accommodation was seen in the owls. Corneal accommodatio n ranging from 2.8 to 6.2 D in magnitude was recorded in a number of t he hawks. These differences in the accommodative behaviors of the owls and hawks are discussed with respect to the limitations of the behavi oral techniques used, differences in the degree of cooperation of the different species, and real differences in the accommodative abilities of the owls and hawks in relation to their accommodative needs, such as when feeding.