Evaluation of healthy equine eyes by use of retinoscopy, keratometry, and ultrasonographic biometry

Objective—To assess natural variations in degree of refraction, corneal curvature, corneal astigmatism, corneal radius, and intraocular distance of healthy equine eyes. Animals—159 horses with healthy eyes that were admitted to a veterinary teaching hospital for nonophthalmic surgeries. Procedures—Eyes of horses were examined with a retinoscope prior to anesthesia and with a keratograph and A- and B-scan ultrasonographic biometers during surgery. In addition, manual caliper measurements of horizontal and vertical corneal radii were obtained. Results—Mean ± SD degree of refraction in the horizontal meridian of eyes was −0.06 ± 0.68 diopters (D). Vitreous body length and horse age correlated negatively with refraction values. The horizontal corneal radius (15.96 ± 1.28 mm) was larger than the vertical corneal radius (15.02 ± 1.09 mm). Accordingly, the vertical corneal curvature (21.56 ± 1.68 D) was greater than the horizontal corneal curvature (22.89 ± 1.65 D). Axial globe length (40.52 ± 2.67 mm), anterior...