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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.
Evaluation of zones of iris hypoplasia in horses and ponies. Mass-like lesions of the iris were evaluated in 15 horses or ponies of various ages and breeds. Breed or gender predilection was not found. These lesions were most often found in blue irides at the 12 o'clock region. Because the lesions transilluminated and changed shape rapidly with changes in pupillary size, they were hypothesized to be zones of iris hypoplasia. Histologic evaluation of one specimen supported this interpretation. The lesions were not associated with any other ocular or systemic abnormality.
Repair of superior palpebral defect in a horse by use of silicone subdermal implant. A silicone subdermal implant was used in the surgical repair of a superior palpebral defect in a horse. The right superior palpebra was missing from the lateral canthus superiorly to the 1 o'clock position, and a corneal ulcer, anterior uveitis, and right micropalpebral fissure also were observed. Lateral canthotomy and canthoplasty were performed to enlarge the palpebral fissure, and a silicone implant was inserted in the superior palpebra to replace the missing tarsal plate. These procedures resulted in a successful reconstruction, with improvement of palpebral function.
[Adenoma of the pigmented epithelium of the iris with endothelialization and descemetization in the horse]. The authors describe peculiar tumors with brown-white piebald anterior surface, which had grown bilaterally from the corpora nigra (C.N.) of an adult horse and occluded the pupils. The surgical procedure for removing the larger tumor and the postoperative treatment are described. The findings by light and electron microscopy suggest that the tumor represent a so-called adenoma of the iris pigment epithelium. The white patches on its surface consist of newly formed Descemet-like material produced by displaced corneal endothelial cells, which have probably grown on the tumor after contact with t...
Anterior uveal melanoma, with secondary keratitis, cataract, and glaucoma, in a horse. Intraocular melanoma was diagnosed in a 13-year-old horse. Secondary clinical findings included keratitis, cataract, and glaucoma. The eye was enucleated. Follow-up information did not give an indication of metastatic disease.
[Immunotherapy of squamous cell carcinoma of the bovine eye and of equine sarcoid]. Squamous cell carcinomas of the bovine eye and equine sarcoids are briefly reviewed. A single injection of BCG into the tumour results in permanent regression of the lesion in 37 per cent of the cattle, regression followed by recurrence of the tumour in 26 per cent and in progressive growth of the tumour in 37 per cent of the cases. Recurrence may be prevented by repeated injection into the lesion. From 50 to 60 per cent of the cows will remain free from tumours. Equine sarcoids show a complete regression in 70-80 per cent of the cases. Tumours on the limbs show a less satisfactory response (l...
The equine fundus. III: Pathological variants. A wide range of ophthalmoscopic variants are encountered during routine examination of the horse. Some result from minor anatomical anomalies, cause no significant effect on vision and may be considered to lie within the limits of 'biological normality'. Others are a consequence of pathological disruption of the anatomical integrity of the fundus, and may directly or indirectly affect the neurosensory retina and produce some degree of visual deficit. This paper illustrates the ophthalmoscopic appearance of a number of pathological variants of the anatomic fundus, and discusses their possible e...
Bilateral colobomas involving the optic discs in a quarterhorse. THIS report describes bilateral colobomas of the optic discs with associated aberrations in ocular differentiation • and unusual hypopigmentation of the uveal tissues.
Tonometric and tonographic studies in the normal pony eye. Tonometric and tonographic techniques were evaluated in the normal pony and compared to other species. Applanation tonometry was utilised to calculate the ocular ridigity of the normal equine eye. The mean intraocular pressure for the pony eye was established as 23.5 mm Hg (sd +/- 4.5). Comparing the non-anaesthetised and anaesthetised pony eye (xylazine-ketamine and glycerol guaiacolate) no significant change in intraocular pressure occurred (P < 0.49). Mean aqueous outflow facility was 0.88 microliter/min/mm Hg (sd +/- 0.65) which is significantly higher (P < 0.01) than the canine and ...
The equine fundus. II: Normal anatomical variants and colobomata. A wide range of fundic variants are encountered during routine ophthalmoscopic examination of visually normal horses, often causing the examiner difficulty in assessing their clinical significance. Many of these are anatomical variants having no significant effect on visual function, and lie within the limits of normality in the horse. This paper illustrates this range of variants and discusses their anatomical basis and physiological consequences. Colobomata are non-progressive discontinuities in the structure of the anatomic fundus, occasionally noted as incidental findings during ophthalmos...
Nutritionally variant streptococci associated with corneal ulcers in horses: 35 cases (1982-1988). Nutritionally variant streptococci (NVS) are nutritionally deficient viridans streptococci that require pyridoxal for growth. Although NVS are pathogenic in human beings, they have not been considered to be pathogenic in domestic animals. In 1982 and 1983, 24 isolates of NVS were recovered from horses with ulcerative keratitis. A retrospective study was done to determine the incidence of NVS in horses with corneal disease. The medical records of 249 horses (259 eyes) examined for clinical signs of corneal disease were reviewed. Nutritionally variant streptococci were isolated from approximatel...
Peripheral corneal ulcers in the horse. This report involves a retrospective study of five horses with an unusual form of progressive peripheral corneal ulcers. These ulcers were located at the perilimbal region of the cornea and spread both centripetally to mid periphery and circumferentially. Lipping of the epithelial edge was observed often. The depth ranged from superficial to mid stroma. Patients ranged from two and a half to eight years, both sexes, and were referred after a variety of antibacterial therapy. Histories were similar in that all ulcers were initially located adjacent to the limbus in one or more quadrants. No tra...
Follow-up report of a case of surgical aphakia with an analysis of equine visual function. More work is necessary to establish corneal dimensions and retinal structure and neural organisation in the equine eye. This paper reports a case of surgical management of bilateral cataracts in a pony and the results of a survey of refractive error in normal horses. Aspects of accommodation are discussed. It is suggested that a difference in retinal receptor organisation between horse and human eyes could explain the good visual performance of the aphakic pony; and that the degree of blurring of vision in the aphakic situation is less, both in absolute terms and in proportion to presumed norm...
The morphology of the equine iridocorneal angle: a light and scanning electron microscopic study. The present investigation of 20 equine eyes shows that the iridocorneal angle of the horse is characterised by a very distinct pectinate ligament and a large ciliary cleft. The pectinate ligament consists of long and broad pigmented trabeculae which form a firm, flat and dense network that encircles the eye. On meridional sections, the ciliary cleft is visible as a wide triangular space comprising the trabecular meshwork which consists of two parts. The inner part is the larger and forms a three-dimensional network of large pigmented trabeculae with very wide intertrabecular spaces. The outer ...
Treatment of advanced squamous cell carcinomas involving the equine cornea. Corneal squamous cell carcinomas with surface areas of more than 2.0 cm were diagnosed in 26 eyes of 25 horses. The depth of the lesion into the corneal stroma and involvement of the ocular adnexa were important determinants for surgical treatment. Corneal tumors that extended into adjacent palpebral conjunctiva, eyelid, or orbit were not amenable to complete excision, while those that involved only cornea and bulbar conjunctiva were treated surgically by keratectomy and beta radiation. Initial treatment was keratectomy followed by beta radiation on 24 eyes and enucleation of two eyes. Twenty ...
Nonulcerative keratouveitis in five horses. Five horses with severe nonulcerative keratouveitis had corneal lesions characterized by a pink stromal infiltrate that initially appeared in the stroma near the limbus. Unremitting iridocyclitis also was evident. In 3 horses, microscopic lesions consisted of marked corneal stromal fibrosis, with mild to severe inflammatory cellular infiltration. Corticosteroids and mydriatic/cycloplegics applied topically and corticosteroids and nonsteroidal anti-inflammatory medications administered parenterally were used with varying degrees of success to control pain and retain vision.
Evaluation of two applanation tonometers in horses. Comparisons were made of measurements obtained in horses, using 2 applanation tonometers in vivo and in vitro. In vitro comparisons indicated that although neither instrument accurately recorded intraocular pressure (IOP), compared with manometric measurements, results of both instruments indicated linear digression from manometric IOP values that could readily be corrected, thereby accurately estimating IOP in horses. For tonometer 1 (MacKay-Marg), calculated actual IOP = 1.48 - 0.9 mm of Hg; and for tonometer 2 (Tono-Pen), calculated actual IOP = 1.38 + 2.3 mm of Hg. The coefficients of dete...
Combined treatment of ocular squamous cell carcinoma in a horse, using radiofrequency hyperthermia and interstitial 198Au implants. Unilateral ocular squamous cell carcinoma in a horse was treated effectively with a combination of repeated radiofrequency hyperthermia and interstitial radiotherapy. These 2 modalities of treatment are synergistic. Interstitial irradiation was achieved, using 198Au implants to deliver a total dose of approximately 5,000 rads/implant over an area of 1 cm2. Radio frequency hyperthermia was repeated 3 times, and radiotherapy was used twice. Treatment resulted in complete regression of the tumor, and ocular complications have not been seen.
Intraocular silicone prostheses in a dog and a horse with corneal lacerations. Intraocular silicone prostheses were implanted in the eyes of a horse and a dog with traumatic corneal lacerations and protrusion of intraocular contents. Several months after surgery, the horse and dog were tolerating the intraocular prostheses, and the appearance was cosmetically acceptable. This contradicts earlier reports that have cited corneal disease as a contraindication for implantation of intraocular silicone prostheses.
Immunohistochemical investigation of the distribution of immunoglobulins G, A and M within the anterior uvea of the normal equine eye. Distribution of the immunoglobulin (Ig) classes G, A and M within the anterior uvea of eight clinically normal equine eyes was examined using indirect immunoperoxidase labelling. Increased staining intensity of stromal IgG and IgA was observed within the ciliary processes, the iris stroma being relatively free of immunoglobulin. This may reflect anatomical variation in the permeability of the uveal microvasculature to lipid insoluble plasma macro-molecules. Intracellular IgG and IgA were observed within the non-pigmented ciliary epithelium in seven and four of the eight eyes respectively, alth...
Retinal vascular patterns in domestic animals. In this paper a morphological study of the retinal vascular patterns in various species of domestic animals is reported. A classification of these patterns into four well-defined groups is described. In the domestic ruminants, pigs and carnivores the retina contains a compact plexus of blood vessels located in the major part of the light-sensitive portion of the retina (euangiotic or holangiotic pattern). In other domestic animals blood vessels are present only in a smaller part of the retina. In the rabbit, vessels are confined to a broad horizontal band coincident with the area of dispersion...
Silicone ocular prosthesis in horses: 11 cases (1983-1987). Horses experience a number of ophthalmic diseases and injuries that may result in loss of function of the eye. In the treatment of end-stage ophthalmic disease or injury that precludes salvage of the eye, the use of an inert, silicone prosthetic implant is a cosmetic alternative to simple enucleation. Eleven horses treated either by enucleation and insertion of an intraorbital prosthesis (n = 9) or by evisceration and insertion of an intraocular prosthesis (n = 2) were evaluated for postoperative complications and for long-term cosmetic results. Of the 11 horses treated, complication rate was ...
Exophthalmos in a horse resulting from an adenocarcinoma of the frontal sinus. A fifteen-year-old thoroughbred gelding with exophthalmos of the left eye, was found at necropsy to have an adenocarcinoma of the left frontal sinus. The tumour extended caudally through the cribriform plate into the orbit, displacing the eyeball anteriorly.
Morphologic features of the aqueous humor drainage pathways in horses. The iridocorneal angle of the horse was anteriorly lined by a pectinate ligament, consisting of several layers of vertically oriented collagenous beams, that were interrupted by a network of extracellular spaces. The anterior chamber angle consisted mostly of a large uveal trabecular meshwork that was composed of widely-spaced, thick trabeculae. These trabeculae were attached in part posteriorly to extensions of the ciliary body musculature and anteriorly inserted into the prominent pectinate ligament. The corneoscleral trabecular meshwork was shaped hemiobovately and formed the external bound...
