Abstract
To calculate the size and dioptric power of a posterior chamber intraocular lens (IOL) to achieve emmetropia in adult rabbits and to compare the dioptric power calculation results using a proprietary predictive formula to a retinoscopy-based method. Three wild rabbit cadavers, seven pet rabbits with cataracts and ten healthy pet rabbits. Implant size was calculated using a capsular tension ring (CTR) (Acrivet® , Berlin, Germany). Published and cadaveric biometric data were used in the predictive formula. An IOL power-escalation study compared the predicted values to the refraction results of one pet rabbit (P1) fitted with a+41D canine IOL (Acrivet® ) and six pet rabbits (P2-P7) fitted with prototype IOLs (Acrivet® ). Retinoscopy of 10 healthy pet rabbits served as controls. A 13.5mm CTR fitted in all rabbits and permitted the use of a 13mm IOL. The predicted IOL power ranged between +24D and +25D. The +41D IOL resulted in a refraction error of +8D. Progressive recalculation through a calibration formula led to the insertion of three +49D IOLs in two pet rabbits and a refraction of +6D to +8D, followed by seven +58D IOLs in four pet rabbits and a refraction median of 0D (range: -1.5D to +1D). A 13mm prototype IOL of +58D achieves emmetropia and is of adequate size for rabbits. The combined use of a CTR and retinoscopy is a useful method to calculate the size and refractive power of a new, species-specific, veterinary IOL.
Highlights
IntroductionIntraocular lens implants with a fixed dioptric power are commercially available for dogs (+41D), cats (+53.5D) and horses (+14D), and the use of IOLs is considered the standard of care in dogs.[1,2,3,4] A variety of predictive formulas exist for the calculation of the dioptric power of a posterior chamber intraocular lens implant (IOL),[4,5,6] and retinoscopy is commonly used to prove if predicted IOL power achieves emmetropia in implanted animals.[7,8,9] The formulas of Binkhorst and Retzlaff have been used in the past for the IOL dioptric power calculation of dogs, cats and horses.[4,5,6] all formulas depend heavily on the accuracy of the biometric data used in the calculations
(range: -1.5D to +1D) in the implanted rabbits, which compared favorably to the control population. This is the first study to demonstrate the difference between the predicted intraocular lens (IOL) dioptric power calculated through a predictive formula, and the actual IOL power calculated through retinoscopy and a calibration formula
The present study demonstrates that given the varied nature of sources of error for the calculation of the dioptric power of an IOL, the use of a retinoscopy-based method that employs an IOL dioptric power escalation approach, is successful, flexible and relatively rapid in finding the power of a new veterinary IOL that leads to emmetropia
Summary
Intraocular lens implants with a fixed dioptric power are commercially available for dogs (+41D), cats (+53.5D) and horses (+14D), and the use of IOLs is considered the standard of care in dogs.[1,2,3,4] A variety of predictive formulas exist for the calculation of the dioptric power of a posterior chamber intraocular lens implant (IOL),[4,5,6] and retinoscopy is commonly used to prove if predicted IOL power achieves emmetropia in implanted animals.[7,8,9] The formulas of Binkhorst and Retzlaff have been used in the past for the IOL dioptric power calculation of dogs, cats and horses.[4,5,6] all formulas depend heavily on the accuracy of the biometric data used in the calculations. There are no publications in the veterinary literature that describe the calculation originally used to predict the haptic diameter of commercially available veterinary IOLs for dogs, and that might serve to calculate the approximate IOL size of a new implant for a different species
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