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Introduction For over 30 years, veterinary ophthalmologists have been implanting intraocular lenses (IOLs) following cataract extraction to achieve emmetropia and correct hyperopia. The optimal intraocular lens power necessary to achieve

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in Journal of the American Veterinary Medical Association

important role of the lens in optical refraction. 2 , 14 As such, veterinary ophthalmologists have attempted to approximate emmetropia in several species postphacoemulsification by implanting an intraocular lens (IOL). 5 , 8 , 10 , 15 , 16 , 17 Additional

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in American Journal of Veterinary Research

insertion of an IOL implant is considered the standard of care in dogs that have undergone phacoemulsification. 7,8 Development of an IOL implant with appropriate dioptric power to approximate emmetropia after insertion in an eye requires accurate

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in American Journal of Veterinary Research

was used to identify breeds with mean refractive errors that were significantly different from emmetropia. Differences in proportions of dogs with various degrees of anisometropia were analyzed by use of a χ 2 test. Statistical analyses were performed

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in American Journal of Veterinary Research

that the mean resting refractive state of 240 dogs was within 0.25 D of emmetropia, and breeds predisposed to development of myopia were also found. A more recent study 1 of 1,440 dogs found the mean ± SD refractive state of all eyes examined was −0

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in American Journal of Veterinary Research

Abstract

Objective

To measure postoperative anterior chamber depth (ACD), corneal curvature, and refractive state of feline eyes after lens removal and implantation of a prosthetic intraocular lens (IOL) and determine appropriate IOL use in cats.

Animals

8 clinically normal adult cats.

Procedure

A-scan ultrasonic biometry, keratometry, and streak retinoscopy were performed on both eyes of each cat before and after lens removal and implantation of a prosthetic IOL. Three diopter (D) IOL strengths were used: 48, 51, and 60 D. Measurements were recorded for 12 weeks after surgery.

Results

IOL were well tolerated by cats, with no serious complications attributable to implantation or presence of the IOL. The ACD was significantly greater after (8.30 mm) than before (4.97 mm) surgery; however, it became slightly more shallow during the 4 weeks after surgery, suggesting that the IOL shifted anteriorly in the eye. Significant difference in corneal curvature was not detected before or after surgery among eyes with various IOL. Twelve weeks after surgery, eyes with 48-, 51-, and 60-D IOL had mean ± SD refractive state of +2.1 ± 0.49, +0.42 ± 0.20, and -2.6 ± 0.78 D, respectively. Linear regression analysis of refractive state on IOL power for all eyes at 12 weeks after surgery predicted that +52.8-D IOL was necessary to best approximate emmetropia in these cats.

Conclusion and Clinical Relevance

IOL of substantially higher diopter strength than that needed in dogs was required to achieve emmetropia after lens extraction in cats. A 52- to 53-D IOL is required to correct feline eyes to near emmetropia after lens removal. (Am J Vet Res 1998;59:1339–1343)

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in American Journal of Veterinary Research

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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in American Journal of Veterinary Research

SUMMARY

Streak retinoscopy was performed by 5 ophthalmologists on 256 eyes (191 dogs) to determine their postoperative refractive state after cataract extraction. Aphakic and pseudophakic eyes that had been implanted with 1 of 5 intraocular lenses (iol) with dioptric powers ranging from + 14.5 to + 38 diopters (D) were studied. By use of ANOVA, breed and body type of dog and individual performing refraction were found to have no detectable effect on final refractive state. Mean refractive state of aphakic eyes was +14.4 ± 2.10 D. Mean refractive state for different iol powers was as follows: + 14.5 D iol = + 11.54 ± 1.18 D (n = 13); +30 D iol = + 5.15 ± 1.18 D (n = 105); + 34.0 D iol = +3.5 D (n = 1); +36 D iol = +2.34 ± 0.73 D 9 (n = 61); and +38 D iol = + 1.41 ± 0.56 D (n = 28). Residual hyperopia ranged from +0.5 D to +2.5 D with +38 D iol, and no eyes were myopic (overcorrected) by use of any of the iol studied. Linear regression analysis of refractive state on iol power for all dogs predicted that dioptric strength of +41.53 D was necessary to best approximate emmetropia for the population as a whole. Body type of the dog had only slight effect (< 1.0 D) on predicted optimal iol power. Further linear regression analysis of the 7 breeds studied predicted variations from +39.62 to +43.14 D in iol powers necessary to approximate emmetropia. Results of the study support the routine use of canine iol with dioptric strength of approximately + 41.5 D in circumstances in which preoperative biometry and keratometry are not practical. The findings further suggest that, for the specific population of dogs studied, most of the dogs could be corrected to near emmetropia by use of a small range of iol dioptric strengths, irrespective of body type or breed.

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in American Journal of Veterinary Research

SUMMARY

Axial length and corneal curvature were determined by use of A-scan ultrasonography and keratometry on both eyes of dogs of various breeds, sizes, and ages. Mean axial length was 20.43 ± 1.48 mm; axial length was not related to age or sex, but was significantly greater (P = 0.047) in dogs of larger breeds. Mean corneal curvature was 39.94 ± 2.61 diopters. Dogs of large breeds had significantly (P < 0.001) flatter corneas. Mild, roughly symmetric astigmatism was detected in a majority of dogs. Use of mean values in a theoretic artificial intraocular lens power equation suggests that aphakic dogs require an implant of approximately 40 diopters to achieve emmetropia.

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in American Journal of Veterinary Research

Abstract

Objective—To follow the development of the refractive error in the eyes of ostrich chicks from age 0 to day 37 after hatching.

Animals—35 ostrich chicks.

Procedures—Spot retinoscopy was conducted to assess refractive error in ostrich chicks. Seventy eyes of 35 ostrich chicks were examined. Of these, 18 chicks were followed over time. At least 4 serial measurements (at 2- to 7- day intervals) were conducted in each of these chicks from day 1 to 37 after hatching. Seventeen additional chicks were examined on days 0, 3, 12, and 19 after hatching.

Results—Ostrich chicks were myopic at hatching, with a mean ± SD refractive error of −4.47 ± 0.15 diopters (D). The refractive error rapidly decreased during the first week of life, and by day 7 after hatching, chicks were slightly hyperopic, with a mean refractive error of 0.42 ± 0.12 D. After day 7, there were no significant differences in the mean refractive error.

Conclusions—The development of optics in the ostrich eye appears to be unique among animals and is characterized by myopia at hatching, rapid onset of emmetropia, and minimal variation in refractive error among chicks. (Am J Vet Res 2001;62:812–815)

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in American Journal of Veterinary Research