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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.
Bilateral eyelid swelling attributable to lymphosarcoma in a horse. Bilateral swelling of upper and lower eyelids was caused by lymphocytic infiltration in an 8-year-old Thoroughbred mare. The condition worsened with pregnancy and became associated with subcutaneous dissemination of lymphosarcoma at distant sites.
A new Papulaspora species from the infected eye of a horse: Papulaspora equi sp. nov. An unusual fungus, probably traumatically introduced into the eye of a horse while grazing, was studied on various mycological media. Upon examination of colonies the organism produced bulbils and clearly exhibited the characteristics of a new species of Papulaspora, P. equi Shadomy & Dixon.
Bilateral colobomas in a horse. Bilateral true colobomas with retrobulbar cysts located over the optic nerves are described in an 8-year-old Quarterhorse mare with a history of progressive blindness. Colobomas result from the failure of an embryonic fissure to close and retrobulbar cysts result from eversion of the neuroectoderm through the colobomas. It could not be determined whether the small optic nerves and the scars, rosettes and disorganization of the cell layers in the retina were the result of concurrent dysplasia or were secondary to degeneration.
Aqueous drainage paths in the equine eye: scanning electron microscopy of corrosion cast. The anterior vasculature of the pony eye was examined by the corrosion cast method. The anterior segment of the pony eye has a vascular pattern which is similar but distinct from that of other mammalian species. Large iridal veins collateralized directly with the anterior vortex venous system. The intrascleral plexus was present but formed a fine, radially oriented, extensive network. This contrasted to the circumferential larger-diameter intrascleral plexus noted in dogs and the canal of Schlemm present in primates. The intrascleral plexus only drained posteriorly in the pony as compared to t...
Equine ocular pathology ascribed to Onchocerca cervicalis infection: a re-examination. Eyes from 292 old (15-20 years) horses originating in the eastern, southeastern and midwestern United States were examined for the presence of Onchocerca cervicalis microfilariae (mf) and concurrently for anterior and posterior segment ocular pathological changes. One-hundred-fifty-three animals (52.4%) were positive for dermal mf (range 0.03-5,364/mg). Of these, 60 animals had anterior segment changes. An additional 58 animals with pathological changes had no dermal mf. Mf were recovered from the ocular tissues of 18% of animals (range 0.07-29/mg). All animals with ocular mf were positive for...
Effect of topical phenylephrine on the equine pupil. The mydriatic effect of 10% phenylephrine was evaluated in 9 horses. Base-line pupillary size in mesopic conditions and during light stimulation was ascertained before application of pharmacologic agents. In study 1, 10% phenylephrine was applied to each eye (n = 5 horses). After 15 minutes, the pupillary size was determined in both lighting conditions. Phenylephrine was again applied to each eye, and after an additional 15 minutes, the pupillary size was determined. In study 2, 1% tropicamide was applied to each eye (n = 4 horses), and after 30 minutes, the pupillary size was determined in bo...
Malignant teratoid medulloepithelioma in a horse. Enlargement of the left eye, corneal opacification, and blindness were clinical signs of a teratoid medulloepithelioma in a 5-year-old Standardbred mare. Diagnosis was made on histologic examination of the enucleated eye. Medulloepitheliomas are congenital intraocular tumors arising from primitive ciliary body epithelium. Their development is rare in domestic animals.
Tears and aqueous humor from horses inoculated with Leptospira contain antibodies which bind to cornea. An antigenic relationship between Leptospira interrogans and equine cornea was previously described by us. An enzyme-linked immunosorbent assay was employed in the present work to investigate the existence of anti-leptospira and anti-cornea antibodies in tears, aqueous humor and serum from horses inoculated i.m. with those antigens. Ten days after a booster by the same route, antibodies that bind to microtiter plates, coated with an homogenate of either equine cornea or leptospira, were detected in those fluids and in the sera. At the same time, the corneas of the horses began to develop a dif...
The optics of comparative ophthalmoscopy. One factor peculiar to the practice of comparative ophthalmoscopy is the very large variation in ocular size of the animals examined, a factor which is ignored in current textbook treatments of the subject. We have computed values of lateral magnification, axial magnification, angular field of view and linear field of view for 19 species of terrestrial vertebrates. The dimensional value of a 1 diopter change in direct ophthalmoscopic focus was also determined. The anterior focal length of the eye in air and the vitreal refractive index were the intrinsic optical parameters of the animal's eye ...
Unconventional aqueous humor outflow of microspheres perfused into the equine eye. Normal drainage of aqueous humor from the anterior chamber of the equine eye occurred through conventional and unconventional routes. To determine the degree of uveoscleral outflow in the pony, 1- and 3-microns (diam) microspheres were perfused through the anterior chamber for 60 and 90 minutes. Two eyes were treated with pilocarpine before perfusion of spheres to observe any effect on outflow. Presence of spheres was detected by scanning electron microscopy and verified by light microscopy. By 60 minutes of the perfusion, 1- and 3-microns spheres thoroughly infiltrated the anterior uveal trab...
Ocular angiosarcoma in four horses. In 4 horses with ocular angiosarcomas, the common characteristics were that all horses were aged, and the neoplasms developed initially on conjunctival surfaces, grew slowly, and metastasized despite excision and radiation treatment. Histopathologically, the neoplasms were of 2 types: a capillary pattern of scant stroma and endothelial-lined vascular channels, and a solid pattern composed of sheets of pleomorphic cells with hyperchromatic nuclei and poorly defined cytoplasmic borders. Definitive diagnosis was made by use of factor VIII:RAg, which stained the tissues intensely.
Ocular angiosarcoma in the horse: morphological and immunohistochemical studies. Angiosarcomas arising in ocular tissues of four aging horses are described. Tumors were locally invasive and eventually metastasized via the mandibular and cervical lymph nodes. Pathologically, the tumors contained well-differentiated regions, in which vascular channels were lined by pleomorphic endothelial cells, as well as poorly-differentiated regions, in which vascular channels were either rudimentary or absent. Red blood cells were scare in vascular structures formed by the tumors. Factor VIII related antigen (VIII:RAg), a blood vascular endothelial marker, was demonstrated by immunohisto...
Eyeworms (Thelazia lacrymalis) in one- to four-year-old Thoroughbreds at necropsy in Kentucky (1984 to 1985). From Mar 1, 1984, to Feb 28, 1985, both eyes from 189 one- to four-year-old Thoroughbreds (88 males, 90 females, and 11 geldings) in Kentucky were examined at necropsy for eyeworms. Thelazia lacrymalis was recovered from 45% of 1-year-old horses, 26% of 2-year-old horses, 45% of 3-year-old horses, and 50% of 4-year-old horses; overall, 43% of 1- to 4-year old horses were infected. Prevalence of eyeworms in horses in the present study was comparable with that in horses of similar ages examined at necropsy in Kentucky in 2 previous studies (1975 to 1976 and in 1979), except for the lower percent...
Effect of xylazine and ketamine on intraocular pressure in horses. Intraocular pressure was measured with a MacKay-Marg tonometer in eight horses following auriculopalpebral nerve block and topical application of lignocaine. Measurements were recorded before and after xylazine, 1.1 mg/kg intravenously, every two minutes for 16 minutes after administration of ketamine, 2.2 mg/kg intravenously, and after recovery from anaesthesia. Before xylazine, intraocular pressure was 17.1 +/- 3.9 and 18.4 +/- 2.2 mm Hg in the left and right eyes, respectively. Intraocular pressure tended to decrease after administration of xylazine and ketamine, with a significant decrease...
Ulcerative keratitis associated with Salmonella arizonae infection in a horse. Salmonella arizonae 61:1,5, was isolated in pure culture from the eye of a horse with unilateral ulcerative keratitis. The eye responded well to treatment with atropine sulfate and polymyxin B-bacitracin-neomycin ophthalmic ointments. In swab specimens taken after the lesion had healed, Salmonella was not found to be a constituent of the bacterial flora of the horse's eyes.
Prevalence of some internal parasites recovered at necropsy of Thoroughbreds born in 1982 in Kentucky. A total of 89 Thoroughbreds, 14 to 333 days old (born in 1982), were examined at necropsy for certain internal parasites during a 1-year-period, Mar 1, 1982, to Feb 28, 1983. The eyes of 73 of the horses and the cranial mesenteric arteries of 71 were examined. Specific interest was on prevalence of parasites according to month of the year and age of the horses at necropsy. Parasites recovered (first month-last month infected horse found) were as follows: Thelazia lacrymalis (eyes) immature and mature (June - February); Habronema/Draschia (lungs) immature (May - September); Habronema muscae (st...
Fundus examination of the horse. This article outlines various conditions affecting the fundus of horses, their symptoms, and associations. The conditions discussed include retinal hemorrhages in newborns, retinal detachments, inflammation, optic neuritis, and congenital stationary […]
Effect of flunixin meglumine on prostacyclin accumulation in the equine eye. A study was performed to identify prostacyclin (PGI2) in equine aqueous humor, demonstrate an increase in PGI2 following anterior chamber paracentesis, and determine the effects of subconjunctival injection of flunixin meglumine on PGI2 accumulation. Twenty ponies were found to be normal upon ocular examination and were placed under general anesthesia. Anterior chamber paracentesis was performed in both eyes (right and left); immediately afterward, 25 mg of flunixin meglumine was injected (subconjunctivally) in the left eye. Aqueous paracentesis was performed 1.5 hours later (both eyes). Aqueo...
