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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.
Duration of corneal anaesthesia following multiple doses and two concentrations of tetracaine hydrochloride eyedrops on the normal equine cornea. There is a clinical impression that tetracaine hydrochloride (THCl) eyedrops is a suitable topical anaesthetic in horses. Objective: To determine the duration of corneal anaesthesia following instillation of multiple doses and 2 concentrations of THCl in 10 healthy horses. Methods: The corneal touch threshold (CTT) was determined, in both eyes, before (basal CTT) and after application of one drop of 0.5% THCl, 2 drops at a 1 min interval of 0.5% THCl or one drop of 1% THCl. CTT was measured in mm every 5 min until complete recovery of the basal CTT. Treatments were separated by an interval of ...
Determination of tear break-up time reference values and ocular tolerance of tetracaine hydrochloride eyedops in healthy horses. Tetracaine hydrochloride (THCl) has been reported to cause irritation in dogs. In man, some topical anaesthetics have been shown to disrupt the tear film. Tear break-up time (TBUT) is a useful test allowing an assessment of the quality of the precorneal tear film. Only one TBUT value has been reported in horses with no information on the technique used. Objective: To provide a method for performing the TBUT in horses and to report any side effects of a single application of THCl in clinically normal horses, particularly on the stability of the tear film. Methods: In Study 1, one drop of 0.5 or...
Distensible superficial venous orbital malformations involving the lower eyelid in two horses. 2 horses were examined because of vascular masses involving the lower eyelid. Results: Both horses had a unilateral, fluctuant mass involving the lower eyelid. For horse 1, the mass had been present since birth and had slowly increased in size over time. The mass also changed in size in response to various environmental stimuli, alterations in the position of the horse's head, and digital obstruction of superficial vessels adjacent to the mass. Horse 2 was brought to the hospital for euthanasia, and no historical or antemor-tem data were available. A combination of contrast angiography, Dopple...
Equine recurrent uveitis: the viewpoint from the USA. Equine recurrent uveitis (ERU) is a common disease in horses in the USA. There have been many advances in the treatment of ERU; however, frequent misdiagnosis of ERU occurs in cases of primary corneal or uveal disease. It is critical to remember that primary uveitis (i.e. one bout of inflammation) is a different disease to ERU, which is an immune mediated recurrent uveitis. Standard symptomatic anti-inflammatory therapy is effective to control most cases of ERU; however, some horses require advanced therapy, such as placement of drug delivery devices or removal of the vitreous, when they fail ...
Equine recurrent uveitis: the European viewpoint. Equine recurrent uveitis (ERU) has always been and still is an important disease with a significant impact on the horse industry in Europe, with a prevalence of 8-10%. The need to understand and manage the disease has spurred the development of veterinary ophthalmology in general, although the aetiology of the disease remains the subject of intense discussion. It is most probably an autoimmune disease triggered, at least in Europe, in the majority of cases by Leptospira spp. The therapy of ERU has evolved over the centuries from various methods of bloodletting to rational medical therapy using...
Current developments in equine cataract surgery. The purpose of this review is to discuss the evolution of equine cataract surgery over the past 50 years to its current stage. Equine cataract surgery is performed similarly compared with the techniques used in human ophthalmology and in other veterinary species. However, enough differences exist to make surgical lens removal and intraocular lens implantation in the horse an intrinsically unique endeavour. Due to the size of the adult equine globe, the introduction of species-specific instrumentation has provided the cornerstone to many of the changes made regarding surgical technique over the...
Neuro-ophthalmology: a review. Evaluation of horses for eye problems and for suspected impairment of visual acuity often requires a thorough neuroophthalmic examination to be conducted. Along with a full ophthalmic evaluation, the results of such an examination should indicate the likely site of any lesion(s) accounting for blindness, miosis, mydriasis, anisocoria, Horner's syndrome, strabismus, facial paralysis and facial spasm, nystagmus and other signs of vestibular disease, and cerebellar disorders, that may be present. Such a thorough examination with guidance for correct interpretation of findings is given here.
Equine glaucoma: state of the art. Understanding and awareness of equine glaucoma has significantly improved in recent years. The availability of portable tonometers and veterinarian/owner awareness has increased the frequency of glaucoma as a clinical diagnosis. A variety of medications for the medical management of equine glaucoma have been evaluated and the addition of lasers has improved the surgical treatment of equine glaucoma. Despite this, equine glaucoma is an insidious and painful disease that probably remains under diagnosed and often results in blindness in the affected eye.
Mitomycin C, with or without surgery, for the treatment of ocular squamous cell carcinoma in horses. Ocular lesions in horses, confirmed as squamous cell carcinoma, were treated topically with mitomycin C. Fourteen horses with confirmed ocular squamous cell carcinoma, three of which were affected bilaterally, were included in the study. Eight of the affected eyes were treated topically with mitomycin C alone; in the other nine eyes, the tumours were surgically removed and topical treatment with mitomycin C was then applied. The treatment protocol consisted of 0.2 ml of 0.04 per cent mitomycin C instilled into the conjunctival sac of the affected eye, every six hours, in rounds of seven days o...
Pythium insidiosum: an overview. Pythium insidiosum is an oomycete pathogenic in mammals. The infection occurs mainly in tropical and subtropical areas, particularly in horses, dogs and humans. Infection is acquired through small wounds via contact with water that contains motile zoospores or other propagules (zoospores or hyphae). The disease, though described as emerging has in fact already been described since 1884. Depending on the site of entry, infection can lead to different forms of pythiosis i.e. a cutaneous, vascular, ocular, gastrointestinal and a systemic form, which is rarely seen. The infection is not contagious...
Measurement of phenol red thread tear test in Arabian and throughbred horses. To determine physiologic levels of tear production in Arabian (AH) and throughbred horses (TH) by using phenol red thread test (PRT). Methods: The study was performed on 16 AH and 14 TH, ranging from 2.5 to 24 years of age, housed in a stable situated in the Sanliurfa of Turkey. Methods: For the measurement of PRT, the strip was placed under the lower eyelid approximately one-third the distance from the temporal to nasal canthus and left for 15 s. The length of the wet area was measured in mm and compared among breed, sex, and age groups and between eyes of both sides. Results: The mean length...
Evaluation of 30- and 25-diopter intraocular lens implants in equine eyes after surgical extraction of the lens. To determine appropriate intraocular lens (IOL) implant strength to approximate emmetropia in horses. Methods: 16 enucleated globes and 4 adult horses. Methods: Lens diameter of 10 enucleated globes was measured. Results were used to determine the appropriate-sized IOL implant for insertion in 6 enucleated globes and 4 eyes of adult horses. Streak retinoscopy and ocular ultrasonography were performed before and after insertion of 30-diopter (D) IOL implants (enucleated globes) and insertion of 25-D IOL implants (adult horses). Results: In enucleated globes, mean +/- SD lens diameter was 20.14 ...
Evaluation of healthy equine eyes by use of retinoscopy, keratometry, and ultrasonographic biometry. To assess natural variations in degree of refraction, corneal curvature, corneal astigmatism, corneal radius, and intraocular distance of healthy equine eyes. Methods: 159 horses with healthy eyes that were admitted to a veterinary teaching hospital for nonophthalmic surgeries. Methods: Eyes of horses were examined with a retinoscope prior to anesthesia and with a keratograph and A- and B-scan ultrasonographic biometers during surgery. In addition, manual caliper measurements of horizontal and vertical corneal radii were obtained. Results: Mean +/- SD degree of refraction in the horizontal mer...
Semiconductor diode laser transscleral cyclophotocoagulation for the treatment of glaucoma in horses: a retrospective study of 42 eyes. To evaluate the outcome of diode laser transscleral cyclophotocoagulation (TSCP) for the treatment of glaucoma in horses. Methods: Medical records at The Ohio State University were reviewed. All horses that underwent diode laser TSCP between the years of 1995 and 2007 were included. Preoperative, procedural and clinical follow-up data were collected, and telephone follow-up was performed. Results: Forty-two eyes of 36 horses were included. Twenty-four hours prior to surgery mean intraocular pressure (IOP) was 37.17 + or - 13.48 mmHg (42 eyes). Forty-one of 42 eyes (98%) were sighted and 39 of ...
Ulcerative keratitis in thoroughbred racehorses in Japan from 1997 to 2008. To describe the number of cases, etiologies, healing times, and results of microbial culture and susceptibility testing of corneal ulcers in thoroughbred racehorses in Japan. Methods: Retrospective study of the medical records of racehorses belonging to the Japan Racing Association (JRA) from 1997 to 2008. Results: A total of 2846 horses suffered ulcerative keratitis. These horses accounted for 90.5% of all the corneal problems and 54.9% of the entire number of horses with ocular diseases. Running in races was the cause in 64.3% of the cases. The mean healing time of the ulcers developed in ra...
Aqueous humor and plasma concentrations of ciprofloxacin and moxifloxacin following topical ocular administration in ophthalmologically normal horses. To determine the degree of ocular penetration and systemic absorption of commercially available topical ophthalmic solutions of 0.3% ciprofloxacin and 0.5% moxifloxacin following repeated topical ocular administration in ophthalmologically normal horses. Methods: 7 healthy adult horses with clinically normal eyes as evaluated prior to each treatment. Methods: 6 horses were used for assessment of each antimicrobial, and 1 eye of each horse was treated with topically administered 0.3% ciprofloxacin or 0.5% moxifloxacin (n = 6 eyes/drug) every 4 hours for 7 doses. Anterior chamber paracentesis wa...
Return to work following unilateral enucleation in 34 horses (2000-2008). REASONS FOR STUDY: The effect of unilateral enucleation on vision and potential loss of performance in horses has received little study. Objective: To evaluate the likelihood of return to prior discipline following unilateral enucleation in horses, assessing the role of age at enucleation, equine discipline, reason for enucleation, time to vision loss and eye enucleated. Objective: Unilateral enucleation has no significant effect on likelihood of return to work in horses, for both right and left eyes, across age and discipline. Methods: A retrospective review of medical records identified 92 h...
Iris abscesses with and without intralenticular fungal invasion in the horse. To describe clinical and histologic findings in horses with iris abscesses. Design Retrospective medical records study. Methods: 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. Methods: 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 warmblo...
Extra-adrenal paraganglioma of the equine orbit: six cases. At The Ohio State University from 1994-2006 six of seven horses evaluated for primary orbital disease were diagnosed with extra-adrenal paraganglioma (EAPG). The horses ranged in age from 14 to 24 years, with a mean of 16.8 years. Duration of clinical signs was 1.5 years to 5 years, with a mean of 2.8 years. Clinical signs varied, but all six had non-painful exophthalmus of the right eye. Five horses had complete ocular exams reported; three of five had decreased to absent vision, two of five had pale optic nerves, and in three of five, difficulty of retropulsion of the globe was noted. Diagno...
Congenital ocular anomalies in purebred and crossbred Rocky and Kentucky Mountain horses. This abstract gives a critique of a research study on ocular anomalies in Rocky and Kentucky Mountain Horses. The author identifies various flaws in the study, arguing that poor sample [...]
Infrared digital imaging of the equine anterior segment. Ocular photographs are an increasingly important method of documenting lesions for inclusion in medical records, teaching purposes, and research. Availability of affordable high-quality digital imaging equipment has allowed for enhanced capture of desired images because of immediate on-camera viewing and editing. Conversion of the standard digital camera sensor to one that is sensitive to infrared light (i.e. > 760 nm < 1 mm wavelength) can be done inexpensively. In the equine eye, advantages of infrared digital photography include increased contrast of anterior segment images, identific...
Bilateral intraocular glandular choristomas in a Thoroughbred foal. Intraocular choristomas are rare anomalies in domestic animals and are often associated with multiple ocular malformations. A Thoroughbred foal presented for ocular abnormalities and was diagnosed with microphthalmia, corneal dermoids, severe anterior segment dysgenesis (including glandular choristomas), aphakia, retinal dysplasia, and optic nerve hypoplasia. Morphological, histochemical, and immunohistochemical comparisons were made between ocular choristomatous tissues from this foal and lacrimal gland, third eyelid gland, nasopharynx, trachea, and lacrimal sac/nasolacrimal duct from normal ...
Circadian intraocular pressure rhythms in athletic horses under different lighting regime. The present study was undertaken to investigate the existence of intraocular pressure (IOP) rhythms in athletic thoroughbred horses maintained under a 24 h cycle of light and darkness (LD) or under constant light (LL) or constant dark (DD) conditions. We identified an IOP circadian rhythm that is entrained to the 24 h LD cycle. IOP was low during the dark phase and high during the light phase, with a peak at the end of the light phase (ZT10). The circadian rhythm of IOP persisted in DD (with a peak at CT9.5), demonstrating an endogenous component in IOP rhythm. As previously shown in other mam...
Pleomorphic corneal sarcoma resembling malignant peripheral nerve sheath tumor in a horse. A 14-year-old Haflinger gelding presented with a protruding mass involving the cornea of the right eye. The mass was resected and submitted for histopathologic and immunohistochemical examination. The preliminary diagnosis was corneal sarcoma, most likely fibrosarcoma. The immunohistochemical results confirmed the mesenchymal origin of the neoplastic cells, which were most consistent with a malignant peripheral nerve sheath tumor. Corneal mesenchymal neoplasms are extremely uncommon tumors in human beings and domestic animals. The cause for this tumor was not determined; infection with bovine ...
Equine Multiple Congenital Ocular Anomalies maps to a 4.9 megabase interval on horse chromosome 6. Equine Multiple Congenital Ocular Anomalies (MCOA) syndrome consists of a diverse set of abnormalities predominantly localized to the frontal part of the eye. The disease is in agreement with a codominant mode of inheritance in our horse material. Animals presumed to be heterozygous for the mutant allele have cysts originating from the temporal ciliary body, peripheral retina and/or iris. In contrast, animals predicted to be homozygous for the disease-causing allele possess a wide range of multiple abnormalities, including iridociliary and/or peripheral retinal cysts, iridocorneal angle abnorm...
Ocular distribution and toxicity of intravitreal injection of triamcinolone acetonide in normal equine eyes. To determine ocular distribution and toxicity of a single injection of intravitreal triamcinolone acetonide (TA) in normal horses. Methods: Six adult horses, donated to North Carolina State University. Methods: Six horses were injected intravitreally with either 10, 20, or 40 mg (n = 2 each) of TA. The opposite eye of each horse was injected with balanced salt solution (BSS). Ocular toxicity was assessed by biomicroscopy, tonometry, indirect ophthalmoscopy, and electroretinogram. Aqueous humor (AH), vitreous humor (VH), and plasma samples were collected. Horses were euthanized 7 or 21 days aft...
Photodynamic therapy for the treatment of periocular squamous cell carcinoma in horses: a pilot study. Local photodynamic therapy (PDT) is a novel cancer therapy in veterinary ophthalmology. A prospective pilot study seeking to demonstrate proof of principle and safety for the treatment of equine periocular squamous cell carcinoma (PSCC) was therefore conducted. We hypothesized that surgical excision with adjunctive local PDT is an effective and safe treatment for equine PSCC. Methods: Nine horses (10 eyes) with PSCC were treated with surgical resection, local infiltration of resulting wound beds with 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a (HPPH) and irradiation with 665-nm wavelength ...
Ocular and multicentric lymphoma in a young racehorse. A 6-year-old thoroughbred gelding was presented with a history of blepharospasm and opacity in the OS of 1 weeks' duration. Ophthalmic examination findings were consistent with acute uveitis in the OS, and traditional treatment was initiated with systemic antibiotics and anti-inflammatory drugs, topical mydriatics, and corticosteroids. During the total treatment period of 4 weeks response to treatment was weak and the horse developed further problems such as cellulitis of the right hind limb with fever and eventually weight loss and dependent edema. Blood work was indicative of liver disease. ...
Epibulbar melanoma in a foal. A case of epibulbar melanoma in a 6-month-old, gelded, chestnut Hanoverian foal is reported. The location and clinical appearance upon initial presentation led to the tentative diagnosis of staphyloma or a congenital mass of unknown origin. An attempt was made to surgically excise the mass under general anesthesia, but due to its infiltrative nature and intraoperative appearance, most, but not all was removed without compromising the integrity of the globe. Histopathological evaluation revealed a multinodular to packeted, poorly demarcated, unencapsulated, infiltrative exophytic melanocytic ne...
Daily rhythm of tear production in normal horse. This study was designed to assess the daily rhythm of tear production in clinically healthy horses, to compare left eye and right eye, and to evaluate the influence of time and gender. Methods: For our study 18 horses (nine female and nine male) were subjected to three different light/dark (L/D) schedules: 12/12 L/D cycles, constant light (24/0 L/D) and constant darkness (0/24 L/D). Methods: In all subjects Schirmer tear tests were performed at 4-h intervals over a 24-h period. Results: A circadian rhythm of tear production was found during the 12/12 L/D period and during constant darkness. Al...
