Mary Lassaline

Interval prevalence of and factors associated with colic in horses hospitalized for ocular or orthopedic disease

OBJECTIVE To determine interval (1-year) prevalence of and factors associated with colic in horses hospitalized for ocular or orthopedic disease. DESIGN Cross-sectional study. ANIMALS 105 horses with ocular disease and 197 horses with orthopedic disease admitted to a veterinary teaching hospital between July 1, 2011, and June 30, 2012. PROCEDURES Medical records were reviewed to determine whether colic (abnormal behavior prompting abdominal palpation per rectum or nasogastric intubation) was observed during hospitalization. Data were collected on putative risk factors for colic, including reason for admission, signalment, and medical or surgical interventions received. RESULTS No significant difference in interval prevalence of colic was identified between horses with ocular disease (8/105 [8%]) or orthopedic disease (9/197 [5%]). However, horses with ocular disease differed significantly from other horses in median age (10 vs 3 years, respectively); proportions of sexually intact males (3% vs 30%), Thoroughbreds (28% vs 62%), and those receiving general anesthesia (65% vs 80%); and median duration of hospitalization (3 vs 2 days). For every 1 mg/kg increase in daily NSAID dose, the odds of colic increased by 98%. No difference between groups was identified in median duration of colic (1 day), hospitalization (7 vs 3 days), or systemic NSAID administration (7 vs 5 days). Colic in both groups resolved with medical management for all but 1 horse with ocular disease. CONCLUSIONS AND CLINICAL RELEVANCE Horses hospitalized for ocular disease were at no greater odds for colic than were horses hospitalized for orthopedic disease. Medical management of colic appeared adequate for most horses.

A missense mutation in damage-specific DNA binding protein 2 is a genetic risk factor for limbal squamous cell carcinoma in horses

Squamous cell carcinoma (SCC) is the most common cancer of the equine eye, frequently originating at the limbus, with the potential to invade the cornea, cause visual impairment, and result in loss of the eye. Several breeds of horses have a high occurrence of limbal SCC implicating a genetic basis for limbal SCC predisposition. Pedigree analysis in the Haflinger breed supports a simple recessive mode of inheritance and a genome‐wide association study (N = 23) identified a 1.5 Mb locus on ECA12 significantly associated with limbal SCC (Pcorrected= 0.04). Sequencing the most physiologically relevant gene from this locus, damage specific DNA binding protein 2 (DDB2), identified a missense mutation (c.1013 C > T p.Thr338Met) that was strongly associated with limbal SCC (P = 3.41 × 10−10). Genotyping 42 polymorphisms narrowed the ECA12 candidate interval to 483 kb but did not identify another variant that was more strongly associated. DDB2 binds to ultraviolet light damaged DNA and recruits other proteins to perform global genome nucleotide excision repair. Computational modeling predicts this mutation to be deleterious by altering conformation of the β loop involved in photolesion recognition. This DDB2 variant was also detected in two other closely related breeds with reported cases of ocular SCC, the Belgian and the Percheron, suggesting it may also be a SCC risk factor in these breeds. Furthermore, in humans xeroderma pigmentosum complementation group E, a disease characterized by sun sensitivity and increased risk of cutaneous SCC and melanomas, is explained by mutations in DDB2. Cross‐species comparison remains to be further evaluated.

Corneal sensitivity and tear production in 108 horses with ocular disease

PURPOSE To compare corneal sensitivity and tear production in horses with keratitis to horses with other ocular disease. METHOD Retrospective medical record review was used to identify equine patients presented during a 1-year period for an ocular complaint who had Schirmer Tear Test (STT) or Corneal Touch Threshold (CTT) measured. Variables studied included patient age and sex; affected eye; category of presenting ocular complaint (keratitis vs. other ocular complaint); STT; and CTT. Patients with a complaint of ulcerative keratitis, immune-mediated keratitis, and stromal abscess were categorized in the keratitis group. Patients with a complaint of uveitis, as well as lid, lens, or retinal disease, were categorized in the group having other ocular disease. For patients presenting more than once in 2013, only the first visit at which STT or CTT was measured was included. For patients with bilateral disease, STT and CTT of both eyes were averaged. RESULTS A total of 108 patients were included, 45 with keratitis and 63 with other ocular disease. Average age was 13.65 years, with more males (77) than females (31). Adjusted for age, STT in affected eyes did not differ significantly between the two groups (keratitis = 29.92 mm/min; other ocular disease = 27.96 mm/min), but CTT was significantly lower in patients with keratitis (33.78 mm) than in patients with other ocular disease (40.10 mm). CONCLUSIONS Corneal sensitivity may be decreased in patients with keratitis. It is not known whether this is a cause or an effect of corneal disease.

Effect of topical application of 0.5% proparacaine on corneal culture results from 33 dogs, 12 cats, and 19 horses with spontaneously arising ulcerative keratitis

OBJECTIVE To investigate the effect of topically applied proparacaine on bacterial and fungal culture results and to compare cytologic and culture results in patients with ulcerative keratitis. PROCEDURE Corneal samples were collected from 33 dogs, 19 horses, and 12 cats with spontaneously arising ulcerative keratitis. Samples for bacterial (dogs, cats, horses) and fungal (horses) cultures were collected prior to and following application of 0.5% proparacaine or saline. All patients then received a topical anesthetic, and samples were collected for cytology. Frequency of cultivatable bacteria before (Swab 1) and after (Swab 2) application of proparacaine or saline was compared using Fishers exact test. Homogeneity of culture and cytology results was assessed using McNemars test. RESULTS No difference was detected in number of animals from which bacteria were isolated from Swab 1 or Swab 2 for proparacaine (21/37 and 17/37, respectively) or saline (10/27 and 12/27, respectively). Small numbers prevented analysis of fungal culture results in horses between Swab 1 and Swab 2 for proparacaine (2/12 and 1/12, respectively) or saline (both, 1/8). Bacteria were isolated from 10 of 20 horses and detected cytologically in 3 of these; fungi were isolated from 3 of 20 horses and detected cytologically in 2 of these. Bacteria were detected more frequently using culture (31/64) than cytology (19/64). CONCLUSION Proparacaine did not significantly alter bacterial or fungal culture results in cats, dogs, or horses; however, clinical significance warrants investigation. Culture and cytology provided complementary data; both should be performed to maximize organism detection in patients with ulcerative keratitis.

Limbal squamous cell carcinoma in a Rocky Mountain Horse: Case report and investigation of genetic contribution

OBJECTIVE To document a case of limbal squamous cell carcinoma (SCC) in a Rocky Mountain Horse stallion determined to be homozygous for the genetic risk factor (DDB2 c.1013C>T) strongly associated with the disease in Haflinger and Belgian horses, and to determine the frequency of this allele in a larger population of Rocky Mountain Horses. ANIMALS STUDIED One privately owned Rocky Mountain Horse and 84 Rocky Mountain Horses screened for allelic frequency. PROCEDURES A complete ophthalmic examination was performed on a Rocky Mountain Horse stallion for assessment of a mass affecting the right eye. A clinical diagnosis of suspected limbal SCC was made, and routine keratoconjunctivectomy and adjunctive strontium irradiation were performed. Genotyping for the DDB2 c.1013C > T (rs1139682898) risk variant was performed utilizing an allele-specific PCR assay on DNA isolated from whole blood and hair follicles. RESULTS Histopathology confirmed the limbal mass to be consistent with SCC. The horse was genotyped as homozygous for the DDB2 c.1013C >T risk variant. The frequency of the variant allele among a population of 84 Rocky Mountain Horses was found to be 0.20. CONCLUSION The Rocky Mountain Horse breed possesses the DDB2 variant allele determined to be a significant risk factor for ocular SCC in the Haflinger and Belgian breeds. Genotyping additional Rocky Mountain Horses diagnosed with ocular SCC as well as confirmed healthy controls for this variant should be undertaken to determine whether a significant association exists between ocular SCC and the variant in the Rocky Mountain Horse breed.

Ocular and periocular hemangiosarcoma in six horses

OBJECTIVE To determine the characteristics of and prognosis for ocular and periocular hemangiosarcoma in horses. ANIMAL STUDIED Six horses treated for ocular or periocular hemangiosarcoma. PROCEDURE A retrospective review of medical records from 2007 to 2015 was performed to identify horses with a histologic diagnosis of ocular or periocular hemangiosarcoma. Signalment (age, sex, breed), duration of clinical signs, prior treatment, tumor size and location, medical and surgical treatment including postoperative chemotherapy, follow-up time, and outcome were obtained from medical records. Histopathology was reviewed by a board-certified pathologist. RESULTS In six horses diagnosed with ocular or periocular hemangiosarcoma, no breed, age, or sex was overrepresented. Sites included the temporal limbus (3), third eyelid (2), and uvea (1). With the exception of one horse with uveal hemangiosarcoma, 5/6 horses had lightly pigmented periocular haircoat. Histologic features of ocular hemangiosarcoma in 6/6 cases included high cellularity, nuclear pleomorphism, and inflammation with a mitotic index ranging from 0 to 8 mitoses per 10 consecutive 400× fields. Five of six tumors displayed solar elastosis, indicating ultraviolet light-induced damage to sub-epithelial collagen. Treatment included surgical excision in all cases and was not associated with recurrence in 4/6. Three cases that received ancillary treatment with topical mitomycin C had no postoperative recurrence. Two cases with postexcisional recurrence had histologic evidence of incomplete excision. CONCLUSIONS Complete surgical excision may be associated with resolution of periocular and ocular hemangiosarcoma in horses. Etiopathogenesis may include exposure to ultraviolet light.

Generation of an equine biobank to be used for Functional Annotation of Animal Genomes project

The Functional Annotation of Animal Genomes (FAANG) project aims to identify genomic regulatory elements in both sexes across multiple stages of development in domesticated animals. This study represents the first stage of the FAANG project for the horse, Equus caballus. A biobank of 80 tissue samples, two cell lines and six body fluids was created from two adult Thoroughbred mares. Ante-mortem assessments included full physical examinations, lameness, ophthalmologic and neurologic evaluations. Complete blood counts and serum biochemistries were also performed. At necropsy, in addition to tissue samples, aliquots of serum, ethylenediaminetetraacetic acid (EDTA) plasma, heparinized plasma, cerebrospinal fluid, synovial fluid, urine and microbiome samples from all regions of the gastrointestinal and urogenital tracts were collected. Epidermal keratinocytes and dermal fibroblasts were cultured from skin samples. All tissues were grossly and histologically evaluated by a board-certified veterinary pathologist. The results of the clinical and pathological evaluations identified subclinical eosinophilic and lymphocytic infiltration throughout the length of the gastrointestinal tract as well as a mild clinical lameness in both animals. Each sample was cryo-preserved in multiple ways, and nuclei were extracted from selected tissues. These samples represent the first published systemically healthy equine-specific biobank with extensive clinical phenotyping ante- and post-mortem. The tissues in the biobank are intended for community-wide use in the functional annotation of the equine genome. The use of the biobank will improve the quality of the reference annotation and allow all equine researchers to elucidate unknown genomic and epigenomic causes of disease.

Corneal edema in four horses treated with a superficial keratectomy and Gundersen inlay flap

OBJECTIVE To describe the clinical presentation, treatment, and outcome of four horses with severe corneal edema caused by suspected endothelial disease treated with a superficial keratectomy and Gundersen inlay flap and to determine whether this procedure (i) reduces corneal edema, (ii) reduces ocular pain, (iii) eliminates recurrent corneal ulceration, and (iv) improves vision in these horses. ANIMALS STUDIED Four horses met inclusion criterion of (i) diagnosis with endothelial disease by a board-certified veterinary ophthalmologist and (ii) surgical treatment with a superficial keratectomy and Gundersen inlay flap. PROCEDURE Retrospective medical record review of included horses was used to determine breed, age and sex of included horses, as well as details of medical and surgical therapy, and visual outcome. RESULTS Four horses were presented with a complaint of focal corneal edema that progressed to diffuse corneal edema. Epithelial bullae and ulceration were present in all cases. The disease process was unresponsive to standard medical treatment with a hyperosmotic agent and topical and systemic anti-inflammatories. However, treatment with a superficial keratectomy and Gundersen inlay flap performed under general anesthesia was associated with (i) a significant decrease in corneal edema, (ii) increased comfort, (iii) elimination of corneal ulceration, and (iv) retention of vision postoperatively with little to no need for medical therapy. Follow-up time was 15, 12, 6, and 3 months. CONCLUSIONS The superficial keratectomy and Gundersen inlay flap may provide a surgical alternative to chronic medical treatment of severe corneal edema in horses.

The Science and Practice of Equine Ophthalmology: A Quarter Century Later

It has been 25 years since Steven Roberts edited an issue of Veterinary Clinics of North America: Equine Practice with a focus on ophthalmology. Throughout those 25 years, the science and practice of equine ophthalmology have been challenged by some of the same diseases, including complicated corneal ulcers, fungal keratitis, uveitis, cataracts, glaucoma, and squamous cell carcinoma; however, progress has been made. There have been advances in pharmacology, genetics, diagnostics, imaging, and surgery, some of which are discussed within this issue, that have changed how ocular disease in the horse can be approached. The formation of the International Equine Ophthalmology Consortium, which first met in 2009, has provided a forum for collaboration and the exchange of ideas that previously was not as easily available. The volume of material in the literature, both as peer-reviewed articles and as reviews, has increased exponentially. Opportunities for continuing education are more available than previously. Finally, the sheer number of people engaged in the science and practice of equine ophthalmology has grown to better support the need and includes general equine practitioners, basic scientists, internists, and surgeons as well as ophthalmologists in this field that is truly interdisciplinary. It is hoped the momentum will continue. The goal of this issue is to summarize current knowledge across an array of topics within equine ophthalmology in a format in which each article can stand alone as a valuable source of information, yet together provide a state-of-the-art summary. It has been a privilege to shepherd the current issue from concept to the articles contained within it. These articles represent some of the advances that have been made in the past 25 years as well as the current thinking of some of the individuals who have been deeply engaged in the science and practice of equine ophthalmology

Effects of 0.2% brimonidine and 0.2% brimonidine–0.5% timolol on intraocular pressure and pupil size in normal equine eyes

BACKGROUND Brimonidine is an α2 -adrenergic agonist that decreases aqueous humour production and may increase uveoscleral outflow. It has not been evaluated in normal or glaucomatous equine eyes. OBJECTIVES To evaluate the efficacy and safety of brimonidine in lowering intraocular pressure (IOP), alone and in conjunction with timolol, as a treatment for equine glaucoma by comparing IOP in normal equine eyes treated with brimonidine and brimonidine-timolol, respectively, with IOP in control eyes. STUDY DESIGN A balanced crossover design with 16 horses receiving one of two treatments, brimonidine and brimonidine-timolol, during each of two 10-day study phases, was used. Four horses were randomly assigned to each of four combinations of treated eye (right or left) and drug order within the two 10-day study phases (brimonidine first or brimonidine-timolol first). METHODS Pupil size and conjunctival hyperaemia were assessed twice per day and IOP was measured three times per day using rebound tonometry in both eyes of 16 normal horses throughout two 10-day study periods (brimonidine and brimonidine-timolol) separated by an 18-day washout period. One eye of each horse was treated with brimonidine or brimonidine-timolol and the opposite eye was treated with balanced salt solution (BSS). RESULTS There were no adverse effects and no significant changes in pupil size in normal equine eyes treated with brimonidine or brimonidine-timolol. Average IOP in normal equine eyes treated with brimonidine (25.6 mmHg) was statistically higher than in eyes treated with brimonidine-timolol (24.6 mmHg) or BSS (24.5 mmHg). However, IOP differences were of ≤1 mmHg and thus not clinically important. MAIN LIMITATIONS Horses with normal eyes may not be as sensitive to the IOP-lowering effects of treatment as horses with glaucoma. CONCLUSIONS Brimonidine and brimonidine-timolol are well tolerated in normal horses but do not decrease IOP.