A great horned owl that weighed 1.5 kg (3.3 lb) and that was of unknown sex and estimated age < 1 year was evaluated at the University of Wisconsin Ophthalmology Service for suspected cataracts. The bird had a history of being perched on a fence with limited movement for 3 days. The bird was captured by wildlife rehabilitators for assessment and flew well in a flight cage, although the rehabilitators witnessed the owl occasionally flying into objects. Upon examination, the bird was lean and had pectoral muscle atrophy but no other physical abnormalities. Ophthalmic examination via slit-lamp biomicroscopy revealed prominent nuclear cataracts and multifocal punctate cortical cataracts in both eyes but no evidence of anterior uveitis (Figure 1). The owl had brisk direct pupillary light reflexes, was able to track moving objects, and had a positive menace response in both eyes. Complete fundic examination was hindered by the presence of the cataracts; however, a small degree of chorioretinal pigment clumping was noted nasal to the pecten in the left eye. To determine whether the owl was a candidate for cataract surgery, it received general anesthesia for complete ocular ultrasonography, electroretinography, and collection of blood for analysis. Ocular ultrasonography revealed no evidence of retinal detachment or other ocular defects, and electroretinogram values were within reference limits in both eyes, indicating normal retinal function.1,2 Results of a CBC and blood glucose analysis were within reference limits.
The following day, after induction of general anesthesia, an intracameral injection of 0.05 Mg of atracuriuma into each eye was performed with a tuberculin syringe and needle, entering at the limbus. This procedure was necessary to achieve pupillary dilation to facilitate phacoemulsification.
Bilateral cataract surgery was performed. Following surgical preparation of the eye, a clear corneal incision with a 3.2-mm keratomeb was created to enter the anterior chamber. A clear corneal incision was chosen to avoid the prominent scleral ossicles that extend to the limbus in birds.3 The anterior chamber was filled with viscoelastic agent,c and a 10-mm capsulorrhexis was created in the anterior capsule with a cystotomed and forceps.e To remove the cataract, a combination of routine phacoemulsification with irrigation and aspiration was performed as described.3,4 The corneal incision was extended to a length of 10.5 mm to accommodate the 10-mm optic of the IOL. At this time, the anterior chamber and capsular bag were refilled with viscoelastic agent and the intraocular lensf was inserted and centered in the capsular bag. The IOL was a 1-piece, custom-made PMMA lens with a 17-mm haptic diameter (tip to tip), 10-mm central optic, and power of +13.8 diopters. The dioptric strength (F) for the IOL was calculated with values obtained from the published schematic eye mathematical model for great horned owls and the Binkhorst equation5 as follows:
where a = axial length (38.72 mm), c = corneal curvature (11.608 mm), d = distance from cornea to IOL (15.0 mm), and 1336 = constant for the refractive index of the aqueous humor.
Closure of the corneal incision was performed routinely with 8-0 polyglactin 910g in a simple interrupted pattern, oversewn with a continuous pattern. A subconjunctival injection of triamcinoloneh (0.075 mg) was administered into the posterior aspect of the nictitans, and a temporary tarsorrhaphy with 6-0 silki suture was performed to protect the corneal wound.
After surgery, each eye was treated with topically administered 0.1% neomycin-polymyxin-dexamethasone dropsj at a tapering frequency (q 8 h for 2 weeks, q 12 h for 2 weeks, and q 24 h for 1 week). Fluconazolek (30 mg, PO, q 24 h for 2 weeks; then q 48 h for 2 weeks) was also administered because of the risk of development of systemic aspergillosis following the stress associated with transport, handling, and surgery.6
Minimal intraocular inflammation was detected in either eye at reevaluation 2 weeks and 3 months after surgery, and tracking and feeding behavior improved. Refraction, as evaluated by use of streak retinoscopy 3 months after surgery, was found to be −0.75 diopters in the right eye and −0.25 diopters in the left eye.
Two months after surgery, the owl was able to successfully capture live prey and improved in physical status. After 3 months of rehabilitation, the bird was fitted with a radio transmitter on a biodegradable harness and released back into the region where it had been found. It was successfully monitored for 6 months before the tracking system was lost as planned.
Atracurium, Bedford Laboratories, Bedford, Ohio.
Keratome, Feather Safety Razor Co Ltd, Osaka, Japan.
Viscoelastic agent, Hylartin V, Pharmacia & Upjohn Co, Kalamazoo, Mich.
Cystotome, Oasis, Glendora, Calif.
Utrata forceps, Bausch & Lomb Surgical Inc, San Dimas, Calif.
Intraocular lens, Storz Ophthalmics Inc, Clearwater, Fla.
Vicryl, Ethicon Inc, San Angelo, Tex.
Vetalog, Fort Dodge Animal Health, Fort Dodge, Iowa.
Silk, United States Surgical, Norwalk, Conn.
Neomycin/polymyxin B/dexamethasone 0.1%, Bausch & Lomb, San Dimas, Calif.
Fluconazole, Greenstone Ltd, Peapack, NJ.
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