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Topic:Eyes
The study of equine eyes encompasses various anatomical, physiological, and pathological aspects of the horse's visual system. The equine eye is a complex organ adapted for a wide field of vision and low-light conditions, which is essential for the survival of prey animals. Key components include the cornea, lens, retina, and optic nerve, each playing a role in capturing and processing visual information. Common ocular conditions in horses include uveitis, cataracts, and corneal ulcers, which can affect vision and overall health. Diagnostic techniques such as ophthalmoscopy and ultrasonography are employed to assess eye health and detect abnormalities. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, function, and diseases of the equine eye, as well as advancements in diagnostic and therapeutic approaches.
Treatment and long-term follow-up of distichiasis, with special reference to the Friesian horse: a case series. Distichiasis is very uncommon in horses and treatment options and outcome remain unknown. Objective: To describe treatment and long-term follow-up of distichiasis in the horse. Methods: Retrospective clinical study. Methods: Case records of horses admitted for diagnosis and treatment of uni- or bilateral distichiasis between 2003 and 2012 were reviewed. Long-term (>6 months after last treatment) follow-up was by telephone conversation with the owner or referring veterinarian. Data were analysed using a Chi-squared test. Results: Eighteen cases were identified, of which 17 were Friesians. Al...
Equine multiple congenital ocular anomalies and silver coat colour result from the pleiotropic effects of mutant PMEL. Equine Multiple Congenital Ocular Anomalies (MCOA) syndrome is a heritable eye disorder mainly affecting silver colored horses. Clinically, the disease manifests in two distinct classes depending on the horse genotype. Horses homozygous for the mutant allele present with a wide range of ocular defects, such as iris stromal hypoplasia, abnormal pectinate ligaments, megaloglobus, iridociliary cysts and cataracts. The phenotype of heterozygous horses is less severe and predominantly includes iridociliary cysts, which occasionally extend into the temporal retina. In order to determine the genetic ...
The fibrous tapetum of the horse eye. The tapetum lucidum is a light-reflective tissue in the eyes of many animals. Many ungulates have a fibrous tapetum. The horse has one of the largest eyes of any living animal and also has excellent vision in low-light environments. This study aimed to clarify the macroscopic tapetal shape, relationship between the tapetal thickness and the degree of pigmentation of the retinal pigment epithelium (RPE), spatial relationship between the visual streak and the tapetum, and wavelength of the light reflected from the tapetum in the horse. Macroscopically, weak light revealed the tapetum as a horizo...
A genome-wide association study identifies risk loci to equine recurrent uveitis in German warmblood horses. Equine recurrent uveitis (ERU) is a common eye disease affecting up to 3-15% of the horse population. A genome-wide association study (GWAS) using the Illumina equine SNP50 bead chip was performed to identify loci conferring risk to ERU. The sample included a total of 144 German warmblood horses. A GWAS showed a significant single nucleotide polymorphism (SNP) on horse chromosome (ECA) 20 at 49.3 Mb, with IL-17A and IL-17F being the closest genes. This locus explained a fraction of 23% of the phenotypic variance for ERU. A GWAS taking into account the severity of ERU, revealed a SNP on ECA18 n...
Evaluation of the conjunctival fungal flora and its susceptibility to antifungal agents in healthy horses in Switzerland. To characterize the conjunctival fungal flora and to determine the susceptibility of 2 isolated molds to antifungal drugs in samples of 64 healthy horses from The National Stud in Switzerland. Methods: Conjunctival cytobrush samples were collected from both eyes of 64 ophthalmologically normal horses in August 2012 and subsequently cultured on Sabouraud's agar medium. Growing fungi were identified and counted. Etests or broth microdilution tests for Aspergillus fumigatus and Eurotium amstelodami were carried out to determine antifungal drug sensitivity. These species had previously been detect...
Treatment of immune-mediated keratitis in horses with episcleral silicone matrix cyclosporine delivery devices. To describe the use of episcleral silicone matrix cyclosporine (ESMC) drug delivery devices in horses with immune-mediated keratitis (IMMK) with evaluation of tolerability and efficacy in long-term control of inflammation. Methods: Retrospective study. ESMC implants (1.2 cm length, 30% wt/wt cyclosporine (CsA) in silicone; with approximately 2 μg/day steady-state release for at least 400 days) were used. Results: Nineteen horses (20 eyes) received two or more ESMC implants for superficial stromal (n = 9), midstromal (n = 3), or endothelial (n = 5) IMMK. Three additional horses received two or...
Feasibility of aqueous shunts for reduction of intraocular pressure in horses. Based on the current literature, neither medical, surgical nor combination therapy adequately controls equine glaucoma for many horses. Aqueous shunts have been useful in other species to control glaucoma. Objective: To determine whether aqueous shunts in normal equine eyes significantly reduce intraocular pressure (IOP) without causing vision threatening complications. Methods: Prospective experimental trial. Methods: Aqueous shunts were placed in 7 normal eyes of 4 horses. The shunts were placed dorsotemporally. Examinations were initially performed daily for 7 days and after that every 3 da...
Comparison of ultrasonography and histologic examination for identification of ocular diseases of animals: 113 cases (2000-2010). To compare ultrasonographic and histologic examination findings for eyes of animals with ocular diseases. Methods: Retrospective case series. Methods: 116 eyes of 113 animals examined at 2 facilities. Methods: Diseased eyes of animals were examined by means of ultrasonography, removed via enucleation or exenteration, then histologically examined. Ultrasonographic images and histopathologic slides were evaluated, and diseases of eyes were identified with each of those methods and allocated to various categories. For each disease category, agreement between results of ultrasonography and those o...
Equine glaucoma: a histopathologic retrospective study (1999-2012). To characterize and describe the histopathologic findings in equine globes enucleated due to glaucoma. Methods: Medical records at The Ohio State University from 1999 to 2012 were reviewed retrospectively. Signalment, history, and treatment data were collected, and histologic slides of enucleated globes were examined and lesions recorded. Twenty-three eyes from 23 horses were eligible for inclusion in this study. Results: The majority of affected horses were > 15 years of age (65%). The ages ranged from 5 to 35 years (mean = 17.4 years). The left eye was affected in 10 cases (43%) and the r...
Eosinophilic keratitis in 46 eyes of 27 horses in the Mid-Atlantic United States (2008-2012). To review the signalment, clinical characteristics, treatment, and outcome of equine EK cases in the Mid-Atlantic United States; to evaluate the effects of topical or systemic corticosteroid treatment, oral cetirizine treatment and secondary corneal infection on disease duration; and to evaluate the association between corticosteroid and cetirizine treatment and likelihood of recurrence. Methods: Twenty-seven horses (47 eyes) diagnosed with EK from 2008 to 2012. Methods: Retrospective medical record review followed by phone interview to obtain recurrence data. Results: Average age of affected ...
Anatomical location and culture of equine corneal epithelial stem cells. To identify morphologically the locations of equine corneal epithelial stem cells (CESCs) and to culture these cells. Methods: We studied the eyes of 12 adult thoroughbred horses. Methods: Eye tissues were immunostained for two positive stem cell markers (p63, CK14) and one negative marker (CK3) to identify the locations of CESCs, so we could compare their immunostaining patterns with those of human stem cells previously reported. We compared the proliferation rates and morphological features of epithelial cells isolated from the corneal limbus and central cornea. Results: Undifferentiated cel...
The effect of 1% tropicamide-induced mydriasis and cycloplegia on spherical refraction of the adult horse. To determine the effects of tropicamide 1% on the refractive state of the adult equine globe and identify the most appropriate time period (in relation to mydriasis) to perform streak retinoscopy. Methods: Eight university-owned mares of various ages and breeds. Methods: Topical tropicamide 1% was applied to one randomly selected eye from each of the horses to induce mydriasis and cycloplegia. The contralateral eyes served as controls. Streak retinoscopy and pupillometry were performed prior to, and every 5 min after tropicamide 1% installation for 90 min. Results: All values are expressed as ...
Equine keratomycosis in Switzerland: a retrospective evaluation of 35 horses (January 2000-August 2011). Keratomycosis is a severe disease in horses. Geographical differences in fungi causing keratomycosis and susceptibility of the organisms to antifungal drugs exist but few previous publications on this disease originate from Europe. Objective: To retrospectively compare the clinical data of 36 eyes with keratomycosis, diagnosed in 35 horses between January 2000 and August 2011 at the Vetsuisse Faculty of Switzerland. Case history, season, prior treatment, clinical appearance, surgical and medical treatment, treatment duration, and globe survival were evaluated. Methods: Retrospective case serie...
Ultrasonographic features of PMEL17 (Silver) mutant gene-associated multiple congenital ocular anomalies (MCOA) in Comtois and Rocky Mountain horses. (1) To describe the ultrasonographic appearance of multiple congenital ocular anomalies (MCOA) in the eyes of horses with the PMEL17 (Silver) mutant gene. (2) To compare the accuracy of B-mode ocular ultrasound to conventional direct ophthalmoscopy. Methods: Sixty-seven Comtois and 18 Rocky Mountain horses were included in the study. Methods: Horses were classified as being carriers or noncarriers of the PMEL17 mutant allele based on coat color or genetic testing. Direct ophthalmoscopy followed by standardized ultrasonographic examination was performed in all horses. Results: Seventy-five of 8...
Corneal stromal abscessation in two horses treated with intracorneal and subconjunctival injection of 1% voriconazole solution. To describe and evaluate intrastromal and subconjunctival injection of voriconazole for the therapy of deep corneal stromal abscess (DSA) in horses. Methods: A retrospective clinical study describing the indications for intrastromal and subconjunctival voriconazole injection and the outcomes of this procedure in two eyes of two horses. Methods: The two horses in this study failed to respond to medical therapy. Treatment with intracorneal and subconjunctival administration of 1% voriconazole was performed in this study. Results: Treatment with intracorneal and subconjunctival administration of ...
Fungal polymerase chain reaction testing in equine ulcerative keratitis. To assess the diagnostic utility of fungal polymerase chain reaction (PCR) in forty-three horses with naturally acquired corneal ulcers presenting to a private practice. Methods: Routine evaluation of cytologic, histologic, and microbiologic samples was performed. Two PCR approaches were compared - generic and specific fungal nested PCR followed by sequencing and quantitative PCR (qPCR). PCRs were applied to pure control fungal cultures, corneal tissue from ulcerated eyes and in a subset of 9 horses, to swabs from contralateral normal eyes. Results: The expected fungus was identified by nested...
Association of height, body weight, age, and corneal diameter with calculated intraocular lens strength of adult horses. To determine whether differences exist in the calculated intraocular lens (IOL) strengths of a population of adult horses and to assess the association between calculated IOL strength and horse height, body weight, and age, and between calculated IOL strength and corneal diameter. Methods: 28 clinically normal adult horses (56 eyes). Methods: Axial globe lengths and anterior chamber depths were measured ultrasonographically. Corneal curvatures were determined with a modified photokeratometer and brightness-mode ultrasonographic images. Data were used in the Binkhorst equation to calculate the ...
Predictability of visual perturbation during locomotion: implications for corrective efference copy signaling. In guiding adaptive behavior, efference copy signals or corollary discharge are traditionally considered to serve as predictors of self-generated sensory inputs and by interfering with their central processing are able to counter unwanted consequences of an animal's own actions. Here, in a speculative reflection on this issue, we consider a different functional role for such intrinsic predictive signaling, namely in stabilizing gaze during locomotion where resultant changes in head orientation in space require online compensatory eye movements in order to prevent retinal image slip. The direct...
Ocular disease in working horses in Ethiopia: a cross-sectional study. Ocular disease is a frequent finding in working horses. This study aimed to estimate the prevalence and types of ocular pathology, and explore risk factors potentially associated with disease within a population of working horses in Ethiopia. In total, 1049 horses were selected from horses attending clinics run by the Society for Protection of Animals Abroad (SPANA). Each had an ophthalmic examination conducted under field conditions using a pen-torch. All owners completed a short questionnaire. The prevalence of ocular abnormalities was 23.5 per cent (95 per cent confidence interval (CI) 18.0...
Light microscopic evaluation and scanning electron microscopic analysis of horse eyes following deep anterior lamellar keratectomy. OBJECTIVE To describe the technique of deep anterior lamellar keratoplasty (DALK) with Descemet's membrane (DM) exposure in horse eyes. Also, to compare the efficacy and safety of viscodissection and big-bubble techniques for DALK. ANIMALS STUDIED Thirty-four ex vivo horse eyes. PROCEDURE Deep anterior lamellar keratoplasty was performed in 34 ex vivo horse eyes. Two groups (Group V--viscodissection--2% sodium hyaluronate; Group A--air--big-bubble) of 17 eyes were studied. Other than the substance used, the surgical technique was similar for both groups. Nonperforated eyes were submit...
Benign intraocular teratoid medulloepithelioma causing glaucoma in an 11-year-old Arabian mare. An 11-year-old Arabian mare was presented for investigation of a visible, pale-colored intraocular mass in the right eye. Results: An intraocular mass was detected clinically and ultrasonographically as originating from the superior temporal quadrant of the ciliary body and iris and causing secondary glaucoma. The echodense mass was occupying the majority of the vitreous chamber and extended into the anterior chamber. The left eye appeared normal. Results: Enucleation was recommended for therapeutic and diagnostic purposes. No adjuvant treatment was given. Histopathological examination demonst...
Equine keratomycoses in California from 1987 to 2010 (47 cases). Equine keratomycosis in the western USA has received little study, probably owing to its low prevalence. Objective: To determine clinical features, predominant fungal isolates, treatment modalities and outcomes of horses with keratomycosis in California and compare these with results from different geographic regions. Methods: Records of horses presented to the University of California-Davis Veterinary Medical Teaching Hospital (UCD-VMTH) with confirmed keratomycosis between 1987 and 2010 were reviewed for this retrospective study. Information retrieved from the record included background, oph...
Ocular abnormalities in healthy Standardbred foals. To determine the prevalence and describe ocular abnormalities in healthy Standardbred foals within 48 h of birth. Methods: One hundred and two neonatal foals. Methods: All foals had an unassisted delivery. On the basis of physical examination and the results of hematological and biochemical parameters, all foals were unaffected by systemic diseases. A complete ophthalmic examination was performed within 48 h of birth. Foals with ocular hemorrhages were re-examined weekly until the abnormalities were resolved. Results: 65/102 (63.7%) foals did not show ocular abnormalities, while in 37/102 (36....
A pilot study on the corneal curvatures and ocular dimensions of horses less than one year of age. Intraocular lenses (IOLs) have been implanted in adult equine eyes after cataract surgery. Foals and weanlings comprise a large proportion of those horses undergoing cataract surgery. Due to potential differences in the size and corneal curvature of the juvenile eye, it is not currently known whether implantation of adult IOLs is appropriate in foals and weanlings. The objective of the study was to measure the anterior chamber depth (ACD), central lens thickness (CLT), vitreous chamber depth (VCD), axial globe length (AGL) and corneal curvature of horses less than one year of age. The axial di...
Ocular manifestations of a metastatic adenocarcinoma in a horse. A 10-year-old German Warmblood gelding was referred to the Equine Department of the Vetsuisse Faculty, University of Zurich, Switzerland, for an iris mass OD, lethargy, intermittent fever, and coughing. Ophthalmic examination revealed a 7 × 9 mm raised, fleshy, whitish to pinkish, vascularized iris mass at the 2 o`clock position OD. Fundic examination showed multifocal round, brown to black, slightly raised lesions with indistinct margins and a surrounding hyperreflective zone OU. Physical examination revealed a temperature of 39.2 °C, sinus tachycardia, preputial and ventral edema, and an e...
Lateral vision in horses: a behavioral investigation. This study investigated lateral vision in horses (Equus caballus) for the first time from a behavioral point of view. Three horses were tested using a novel experimental design to determine the range of their lateral and caudolateral vision with respect to stimulus detection and discrimination. Real-life stimuli were presented along a curvilinear wall in one of four different positions (A, B, C, D) and one of two height locations (Top, Bottom) on both sides of the horse. To test for stimulus detection, the correct stimulus was paired against a control; for stimulus discrimination, the correct ...
Diode laser endoscopic cyclophotocoagulation in the normal equine eye. To determine the clinical and histologic effects of diode endoscopic cyclophotocoagulation (ECP) in the phakic equine eye. Methods: Phase I: 10 equine cadaver eyes. Phase II: four normal adult horses. Methods: Phase I: ECP probe angle of reach (AR) was determined. Multiple ECP energy levels: 0.75, 0.90, 1.05, 1.20, 1.35, 1.50 J, and the resulting visible and histologic ciliary process changes were evaluated. Phase II: Ocular quadrants were treated with ECP at 0.90, 1.14, 1.38 J, and a control. The contralateral eye underwent a sham operation. Tissue changes (clinical and histologic) were evalu...
