Cataract extraction is routinely performed in horses. However, an appropriate IOL implant specifically designed for horses has not been developed or evaluated. Because of the current lack of a commercially available and clinically validated IOL implant, cataract removal in horses results in animals that are aphakic, which results in a marked postoperative refractive error (hyperopia).1,2 Although most aphakic horses apparently are able to have typical behaviors and perform functions (with some even returning to their prior level of activity following surgery), compared with behavior and function of horses with intact lenses, there is a paucity of studies1–6 that have been conducted to objectively evaluate vision postoperatively in aphakic horses.
Before the widespread use of IOL implants in dogs undergoing surgical extraction of the lens, it was thought that aphakic dogs had acceptable and functional vision and did not need to receive an IOL implant.a However, following development of the canine IOL implant and subsequent clinical and retinoscopic visual function studies in dogs after IOL implant insertion, it has been determined that the visual acuity of a dog can be returned to normal following lens extraction. Currently, the 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 measurements of species-specific ocular dimensions, such as corneal curvature, AC depth, CLT, AxL, and postoperative AC depth.7–10 Although data for individual ocular dimensions are available, studies conducted to specifically evaluate the globe for the purpose of IOL implant design are limited to those in individual dogs,9 cats,10 and horses.11 In addition to corneal curvature and the measurement of preoperative ocular globe dimensions (ie, AC depth, CLT, and AxL) to calculate the appropriate dioptric power for the IOL implant that is to be inserted, it is necessary to determine the position of the IOL implant relative to the cornea (ie, postoperative AC depth) after insertion.12 In another study,11 the AC depth plus 50% of the CLT value was selected as the postoperative AC depth when calculating the refractive power (dioptric power) necessary for the selection of an appropriate equine IOL implant. The data obtained from that study11 were applied to 2 theoretical formulas13,14 established for humans, which provided a power estimate of approximately 30 D as the dioptric power of the IOL implant necessary to approximate emmetropia in an adult horse. Prototype IOL implants (eg, 30- and 25-D implants) were manufactured on the basis of the curvature of the cornea and ocular dimensions.11
Investigators have reported2,b the implantation of IOLs in adult horses, but calculations of the appropriate dioptric power were not performed before their use. Results of a study15 that was performed by use of a schematic eye,16 the Binkhorst formula,13 and an assumed postoperative AC depth of 13.07 mm were used to estimate that a 22.5-D IOL implant would be appropriate to approximate emmetropia in the eyes of horses. The purpose of the study reported here was to determine the appropriate equine IOL implant dimensions and dioptric power needed to approximate emmetropia in enucleated globes and eyes of adult horses after surgical extraction of the lens.
Axial globe length
Crystalline lens thickness
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Townsend WM, Jacobi S, Bartoe JT. Phacoemulsification and implantation of +14 diopter intraocular lenses in five eyes of four adult horses (abstr), in Proceedings. 39th Annu Meet Am Coll Vet Ophthalmol 2008;413–429.
Acrivet Inc, Hennigsdorf, Germany.
E Technologies Inc, Bettendorf, Iowa.
Electronic digital calipers, Fowler & NSK, Tokyo, Japan.
Tono-Pen Vet, Reichert, Depew, NY.
Heine Optotechnik, Herrsching, Germany.
Luneau SAS, Prunay-Le-Gillon, France.
Aplicare Inc, Meriden, Conn.
First Priority Inc, Elgin, Ill.
Polyglactin 910, Ethicon Inc, Somerville, NJ.
Kowa SL-14, Kowa Ltd, Tokyo, Japan.
Pfizerpen, Roerig, Division of Pfizer Inc, New York, NY.
GentaMax 100, Phoenix Pharmaceutical Inc, St Joseph, Mo.
Banamine, Schering-Plough Animal Health Corp, Union, NJ.
Ranitidine tablets (300 mg), Wockhardt USA Inc, Bedminster, NJ.
GastroGard, Merial Ltd, Duluth, Ga.
Mila International Inc, Erlanger, Ky.
Atropine sulfate ophthalmic solution 1%, E. Fougera & Co, Melville, NY.
Neomycin and polymyxin B Sulfates and dexamethasone ophthalmic suspension, Bausch & Lomb Inc, Tampa, Fla.
Vigamox, Alcon Laboratories Inc, Fort Worth, Tex.
Flurbiprofen sodium ophthalmic solution 0.03%, Pacific Pharma, Irvine, Calif.
Millenium Surgical Corp, Narberth, Pa.
Unique Technologies Inc, Mohnton, Pa.
Epinephrine injection (1:1,000), IMS Ltd, South El Monte, Calif.
Acrivet Biovisc 1.2% hyaluronic acid, Acrivet, Hennigsdorf, Germany.
Alexos, Oertli Instrumente AG, Berneck, Switzerland.
Amneal Pharmaceuticals of NY, Hauppage, NY.
Dormosedan (10 mg/mL), Orion Corp, Espoo, Finland.
Lidocaine hydrochloride 2%, Sparhawk Laboratories Inc, Lenexa, Kan.
Proparacaine hydrochloride ophthalmic solution, 0.5%, Akorn Inc, Buffalo Grove, Ill.
JMP, version 8.0, SAS Institute Inc, Cary, NC.
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