KERATOMETRY, ULTRASONIC BIOMETRY, AND PREDICTION OF INTRAOCULAR-LENS POWER IN THE FELINE EYE

Objective-To determine ocular dimensions (using A-scan ultrasound biom etry) and corneal curvature (using keratometry) in the feline eye and to calculate the appropriate dioptric power for a prototype posterior chamber intraocular lens (IOL) necessary to achieve emmetropia in the eyes of cats undergoing lens extraction. Animals-25 clinically normal adult mixed-breed cats and 10 eyes from 10 clinically normal adult mix ed-breed cat cadavers. Procedure-A-scan ultrasonic biometry was perfor med on both eyes of each live cat. Cats were tranquilized, and keratom etry was performed on each eye. Biometry was performed on the cadaver eyes. Five of the cadaver eyes had the lens extracted and an IOL, desi gned for use in dogs, was implanted. Biometry was repeated to estimate postoperative IOL position. Using 3 theoretical IOL formulas, data fr om biometry, keratometry, and postoperative IOL position were used to predict IOL strength required to achieve emmetropia after lens extract ion in cats. Results-Mean axial length of eyes in live cats was 20.91 +/- 0.53 mm. Mean preoperative anterior chamber depth (ACD) was 5.07 /- 0.36 mm, and mean lens thickness was 7.77 +/- 0.23 mm. Predicted po stoperative ACD was calculated to be 10.84 mm. Measured postoperative ACD in the 5 cadaver eyes was 8.28 mm. Required IOL strength calculate d, using the predicted postoperative ACD, was 73 to 76 diopters. The r equired IOL strength calculated, using the measured postoperative ACD, was 53 to 55 diopters. Conclusions and Clinical Relevance-An IOL of s ubstantially higher diopter strength than that needed in dogs is requi red to achieve emmetropia after lens extraction in average cats; an IO L strength of approximately 53 to 55 diopters will likely be required.