Keratometry, ultrasonic biometry, and prediction of intraocular lens power in the feline eye

Brian C. Gilger From the Department of Companion Animal and Special Species Medicine, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606.

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Michael G. Davidson From the Department of Companion Animal and Special Species Medicine, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606.

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Peter B. Howard From the Department of Companion Animal and Special Species Medicine, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough St, Raleigh, NC 27606.

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SUMMARY

Objective

To determine ocular dimensions (using A-scan ultrasound biometry) 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 mixed-breed cat cadavers.

Procedure

A-scan ultrasonic biometry was performed on both eyes of each live cat. Cats were tranquilized, and keratometry was performed on each eye. Biometry was performed on the cadaver eyes. Five of the cadaver eyes had the lens extracted and an IOL, designed for use in dogs, was implanted. Biometry was repeated to estimate postoperative IOL position. Using 3 theoretical IOL formulas, data from biometry, keratometry, and postoperative IOL position were used to predict IOL strength required to achieve emmetropia after lens extraction 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 postoperative ACD was calculated to be 10.84 mm. Measured postoperative ACD in the 5 cadaver eyes was 8.28 mm. Required IOL strength calculated, using the predicted postoperative ACD, was 73 to 76 diopters. The required IOL strength calculated, using the measured postoperative ACD, was 53 to 55 diopters.

Conclusions and Clinical Relevance

An IOL of substantially higher diopter strength than that needed in dogs is required to achieve emmetropia after lens extraction in average cats; an IOL strength of approximately 53 to 55 diopters will likely be required. (Am J Vet Res 1998;59:131–134)

SUMMARY

Objective

To determine ocular dimensions (using A-scan ultrasound biometry) 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 mixed-breed cat cadavers.

Procedure

A-scan ultrasonic biometry was performed on both eyes of each live cat. Cats were tranquilized, and keratometry was performed on each eye. Biometry was performed on the cadaver eyes. Five of the cadaver eyes had the lens extracted and an IOL, designed for use in dogs, was implanted. Biometry was repeated to estimate postoperative IOL position. Using 3 theoretical IOL formulas, data from biometry, keratometry, and postoperative IOL position were used to predict IOL strength required to achieve emmetropia after lens extraction 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 postoperative ACD was calculated to be 10.84 mm. Measured postoperative ACD in the 5 cadaver eyes was 8.28 mm. Required IOL strength calculated, using the predicted postoperative ACD, was 73 to 76 diopters. The required IOL strength calculated, using the measured postoperative ACD, was 53 to 55 diopters.

Conclusions and Clinical Relevance

An IOL of substantially higher diopter strength than that needed in dogs is required to achieve emmetropia after lens extraction in average cats; an IOL strength of approximately 53 to 55 diopters will likely be required. (Am J Vet Res 1998;59:131–134)

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