Survey of ocular abnormalities in draft horses.

OBJECTIVE: To determine the prevalence of ocular disease in draft horses in the United States. ANIMALS: Draft horses of various breeds and ages. PROCEDURE: Nondilated ophthalmic examination was performed using slit lamp biomicroscopy and indirect ophthalmoscopy. Intraocular pressures were measured when possible. RESULTS: One hundred sixty-five draft horses were examined. Age range: 10 days to 33 years (mean 10.8 years, median 10 years); 87 geldings (52.7%), 71 mares (43.0%), 7 stallions (4.2%); 64 Percherons (38.8%), 51 Belgians (30.9%), 29 Clydesdales (17.6%), 15 Shires (9%), and 6 other draft breed (3.6%). Intraocular pressure: mean 24.7 mmHg OD, range 13-37 mmHg; mean 25.0 mmHg OS, range 11-37 mmHg. Vision-threatening disease was present in 9 horses (5.5%): complete cataracts 1, post-traumatic optic nerve atrophy 1, uveitis and secondary glaucoma 1, retinal detachment 1, large chorioretinal scar 3, phthisis bulbi 2. Non-vision-threatening ocular disease was present in 56 horses (33.9%) involving one or more ocular structures: eyelid trauma/notch defect 14 (8.5%), SCC-type adnexal lesions 12 (7.3%), corneal scars 16 (9.7%), keratitis 6 (3.6%), corpora nigra cyst 15 (9.1%), incipient/punctate cataract 50 (30.3%), vitreous degeneration 10 (6.1%), asteroid hyalosis 1, "bullethole" chorioretinal scars 3, RPE coloboma 1. Linear keratopathy was present in 28 horses (17%) with 2/28 having concurrent vision threatening ocular disease. CONCLUSIONS: Ocular abnormalities, in particular minor cataracts, were relatively common in this population, but not typically vision-threatening. Additionally, this survey demonstrated a greater prevalence of linear keratopathy in draft horses compared with reports in other breeds; however, it does not appear to be associated with concurrent ocular disease.

Additional Evidence for DDB2 T338M as a Genetic Risk Factor for Ocular Squamous Cell Carcinoma in Horses.

Squamous cell carcinoma (SCC) is the most common periocular cancer in horses and the second most common tumor of the horse overall. A missense mutation in damage-specific DNA-binding protein 2 (DDB2, c.1012 C>T, p.Thr338Met) was previously found to be strongly associated with ocular SCC in Haflinger and Belgian horses, explaining 76% of cases across both breeds. To determine if this same variant in DDB2 contributes to risk for ocular SCC in the Arabian, Appaloosa, and Percheron breeds and to determine if the variant contributes to risk for oral or urogenital SCC, histologically confirmed SCC cases were genotyped for the DDB2 variant and associations were investigated. Horses with urogenital SCC that were heterozygous for the DDB2 risk allele were identified in the Appaloosa breed, but a significant association between the DDB2 variant and SCC occurring at any location in this breed was not detected. The risk allele was not identified in Arabians, and no Percherons were homozygous for the risk allele. High-throughput sequencing data from six Haflingers were analyzed to ascertain if any other variant from the previously associated 483 kb locus on ECA12 was more concordant with the SCC phenotype than the DDB2 variant. Sixty polymorphisms were prioritized for evaluation, and no other variant from this locus explained the genetic risk better than the DDB2 allele (P = 3.39 × 10-17, n = 118). These data provide further support of the DDB2 variant contributing to risk for ocular SCC, specifically in the Haflinger and Belgian breeds.

Treatment of nonhealing corneal ulcers in 60 horses with diamond burr debridement (2010-2013).

OBJECTIVE: To review the signalment, clinical characteristics, and outcome of horses with nonhealing corneal ulcers treated with diamond burr debridement (DBD); and to evaluate the role of ulcer duration, size and location, and bandage contact lens (BCL) placement on healing. ANIMALS: From January 2012-April 2013, 60 horses were diagnosed with ulcers classified as nonhealing based on the presence of raised epithelial margins and duration of at least 7 days. PROCEDURE: Retrospective record review. RESULTS: Average age of included horses was 14.68 years, SD 8.17 years. There were three times as many males (45) as females (15), (χ12 = 15, P = 0.001). Forty-eight horses (80%) had nonhealing ulcers uncomplicated by associated corneal disease. In the remaining horses, associated corneal disease included esinophilic keratitis (10%), calcific band keratopathy (5%), endothelial decompensation (1.67%), habronemiasis(1.67%), and lid suture abrasion (1.67%). Average corneal ulcer duration prior to diamond burr debridement (DBD) was 29.0 days (n = 56). Ulcers occurred most commonly in the axial cornea (41%). Fifty-five of 60 horses (92%) healed with DBD. Healing time, defined as time to epithelialization following DBD, averaged 15.5 days, SD 9.32 days, and was not correlated with patient age or ulcer duration, location, or size prior to or following DBD. Healing time was significantly longer for eyes in which a BCL had been placed (n = 28, 19.0 days) than for eyes without a BCL (n = 32, 12.9 days), F(1,58) = 5.543, P = 0.02. DBD was considered a failure for five horses (8%). CONCLUSIONS: DBD may be an effective treatment for nonhealing corneal ulcers in horses.

Uveodermatologic syndrome in a rat terrier.

A 4 yr old intact male rat terrier presented with severe bilateral nonresponsive panuveitis. Bilateral uveitis, blepharospasm, conjunctival hyperemia, diffuse corneal edema, peripheral bullous retinal detachment, and secondary ocular hypertension were noted. Ocular lesions progressed despite aggressive medical treatment and were followed by cutaneous depigmentation and crusting along the nasal planum. Intensive oral and topical anti-inflammatory and topical antiglaucoma medications were administered, but the ocular disease progressed. A bilateral enucleation was performed. Uveodermatologic syndrome was diagnosed from histopathologic examination of a skin biopsy as well as histopathology of both globes after bilateral enucleation. To maintain control of the dermatologic lesions, oral azathioprine was initiated, but it was not well tolerated by this patient. Immunosuppressive doses of oral cyclosporine and anti-inflammatory doses of oral prednisone were used to control the depigmentation and crusting skin lesions.

Cutaneous periocular Habronema infection in a dromedary camel (Camelus dromedarius).

A 6-year-old castrated dromedary camel (Camelus dromedarius) presented with a non-healing, severely pruritic, ulcerative fibrotic plaque located at the medial canthus. Histological examination of surgical biopsies identified degenerating nematode larvae within eosinophilic granulomas. Treatment involved repeated debridement of the lesion, injectable ivermectin and anti-inflammatory therapies, and injectable and topical antibiotics. A specially constructed mask with goggles to prevent the camel from continuing to self-traumatize the eye and lesion was also placed. Full recovery occurred approximately 1 month after diagnosis. Because of the location of the lesion, time of year, the gross and microscopic characteristics of the lesion, the presence of a likely nematode larva and the response to treatment, a diagnosis of cutaneous habronemiasis was made.

Iris abscesses with and without intralenticular fungal invasion in the horse.

OBJECTIVE: To describe clinical and histologic findings in horses with iris abscesses. Design Retrospective medical records study. ANIMALS STUDIED: Medical records of horses that had iris abscesses at the University of Florida Veterinary Medical Center, Peterson & Smith Equine Hospital, and Veterinary Eye Specialists of London, Ontario, from 2005 to 2008 were reviewed. PROCEDURE: Data collected from the medical records included signalment, clinical and histologic descriptions of ocular lesions, therapy, complications, and visual outcomes. RESULTS: The medical records of two Quarterhorses, one pony, one warmblood, one Westphalian, and one Arab horse with unilateral iris abscesses were identified. Mild-to-severe clinical signs of iridocyclitis were present in all six eyes with iris abscesses. The eyes of two horses with iris abscesses were also associated with deep stromal abscesses and responded to medical therapy alone in one case, and medical therapy and corneal transplantation in the other. Iris abscesses in two horses were also associated with intralenticular invasion due to a Cladosporium and a Fusarium-type fungus respectively, and resulted in enucleations. Two horses with iris abscesses and no apparent lens involvement resolved with medical therapy in one case and surgical removal of the iris abscess and medical therapy in the other. CONCLUSIONS: This is the first clinical report of iris abscesses in the horse, and the first histologic report of fungal invasion of the horse lens.

Congenital stationary night blindness in a Thoroughbred and a Paso Fino.

This report documents congenital stationary night blindness (CSNB) in two non-Appaloosa horse breeds (Thoroughbred and Paso Fino). History of vision impairment since birth, normal ocular structures on ophthalmic examination, and electroretinographic findings were consistent with CSNB. In one horse (Thoroughbred), a 9-year follow-up was carried out. In the Paso Fino, severe vision impairment from birth to approximately 1 year of age in both dim and bright light situations led to humane euthanasia and histopathologic confirmation of the disorder.