Congenital ocular abnormalities of Rocky Mountain Horses.
Abstract: OBJECTIVE: To determine the incidence and describe ocular abnormalities in a cross-section of the population of Rocky Mountain Horses. Design: Prospective study. Animals: Five-hundred and fourteen Rocky Mountain Horses. Procedure: Ophthalmic examinations were performed using a slit-lamp biomicroscope and an indirect ophthalmoscope. Intraocular pressures were measured by applanation tonometry. Eyes from six horses were obtained for histologic examination. RESULTS: Cysts of the posterior iris, ciliary body, and peripheral retina were detected most frequently (249 horses), and were always located temporally. Curvilinear streaks of retinal pigmented epithelium extending from the peripheral temporal retina marked the boundary of previous retinal detachment in 189 horses. Retinal dysplasia was detected in 125 horses. Multiple ocular anomalies were evident in 71 horses and were always bilateral and symmetrical. Affected eyes had a large, clear cornea that protruded excessively and had an apparent short radius of curvature, a deep anterior chamber, miotic and dyscoric pupil, and iris hypoplasia. Pupillary light responses were decreased or absent and pupils failed to dilate after repeated instillation of mydriatic drugs in horses with multiple ocular anomalies. Less frequently encountered abnormalities included peripheral iridocorneal adhesions and goniosynechiae. Congenital cataract was always present in eyes with multiple abnormalities. Intraocular pressures did not differ among horses with normal eyes and horses with multiple ocular abnormalities. Histologic examination of eyes corroborated the clinical appearance.
Publication Date: 2001-06-09 PubMed ID: 11397242DOI: 10.1046/j.1463-5224.1999.00050.xGoogle Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
This research aimed to determine and describe the occurrence and nature of eye abnormalities in a population of Rocky Mountain Horses. The study found that multiple eye anomalies, including retinal detachment and iris hypoplasia, were common in these horses, and noted the presence of congenital cataracts in eyes with multiple abnormalities.
Research Design and Procedure
- The researchers carried out a prospective study on a sample of 514 Rocky Mountain Horses.
- They performed ophthalmic examinations on these horses using tools like a slit-lamp biomicroscope and an indirect ophthalmoscope.
- Intraocular pressures were measured using an applanation tonometer. This approach relies on the ‘applanation’ or flattening of the cornea to establish the intraocular pressure.
- For histologic examination, the researchers collected eyes from six horses. Histology involves the study of the microscopic structure of tissues.
Key Findings
- The most common ocular abnormality found was temporal cysts in the iris, ciliary body, and peripheral retina, detected in 249 horses.
- In 189 horses, the researchers noted curvilinear streaks of retinal pigmented epithelium extended from the peripheral temporal retina, marking previous retinal detachment.
- Retinal dysplasia, or the abnormal development of the retina, was present in 125 horses.
- Multiple ocular anomalies were found in 71 horses, and these were always bilateral (affecting both eyes) and symmetrical.
Characteristics of Affected Eyes
- Affected eyes exhibited a large, excessively protruding clear cornea, a deep anterior chamber, a miotic (constricted) and dyscoric (irregularly shaped) pupil, and iris hypoplasia or underdevelopment.
- These eyes showed decreased or no pupillary light responses, and the pupils failed to dilate even after administering mydriatic drugs, which are typically used to enlarge the pupil.
- Congenital cataract was always found in eyes with multiple abnormalities.
- Notably, intraocular pressures did not vary between horses with normal eyes and those with multiple ocular abnormalities.
- The results of histologic examination affirmed the clinical observation of these abnormalities.
Cite This Article
APA
Ramsey DT, Ewart SL, Render JA, Cook CS, Latimer CA.
(2001).
Congenital ocular abnormalities of Rocky Mountain Horses.
Vet Ophthalmol, 2(1), 47-59.
https://doi.org/10.1046/j.1463-5224.1999.00050.x Publication
Researcher Affiliations
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824-1314, USA; Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824-1314, USA; Pathology and Animal Health Diagnostic Laboratory, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824-1314, USA; Veterinary Vision, 219 North Amphlett Blvd, San Mateo, CA 94401, USA; Rood & Riddle Equine Hospital, PO Box 12070, Lexington, KY 40513-1126, USA.
Citations
This article has been cited 18 times.- Allen R, Goodhead AD. A survey of ocular pathology in Warmblood horses in South Africa. Equine Vet J 2025 Jul;57(4):889-897.
- Stas EKL, Hermans H, Slenter IJM, Veraa S, Ensink JM. Noninvasive diode laser-an effective and safe treatment of iris cysts in 46 eyes of 35 horses. Equine Vet J 2023 Mar;55(2):205-213.
- Vercruysse E, Naranjo C, Sauvage A, Vandersmissen M, Grauwels M, Monclin S. Retinal detachment secondary to vitreoretinopathy in two closely related warmblood horses. Open Vet J 2021 Oct-Dec;11(4):672-679.
- Spencer PS. Etiology of Retinal and Cerebellar Pathology in Western Pacific Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex. Eye Brain 2020;12:97-104.
- Bruders R, Van Hollebeke H, Osborne EJ, Kronenberg Z, Maclary E, Yandell M, Shapiro MD. A copy number variant is associated with a spectrum of pigmentation patterns in the rock pigeon (Columba livia). PLoS Genet 2020 May;16(5):e1008274.
- Paschalis-Trela K, Cywińska A, Trela J, Czopowicz M, Kita J, Witkowski L. The prevalence of ocular diseases in polish Arabian horses. BMC Vet Res 2017 Nov 7;13(1):319.
- Johansson MK, Jäderkvist Fegraeus K, Lindgren G, Ekesten B. The refractive state of the eye in Icelandic horses with the Silver mutation. BMC Vet Res 2017 Jun 2;13(1):153.
- Jacobs LN, Staiger EA, Albright JD, Brooks SA. The MC1R and ASIP Coat Color Loci May Impact Behavior in the Horse. J Hered 2016 May;107(3):214-9.
- Andersson LS, Wilbe M, Viluma A, Cothran G, Ekesten B, Ewart S, Lindgren G. Equine multiple congenital ocular anomalies and silver coat colour result from the pleiotropic effects of mutant PMEL. PLoS One 2013;8(9):e75639.
- Hellström AR, Watt B, Fard SS, Tenza D, Mannström P, Narfström K, Ekesten B, Ito S, Wakamatsu K, Larsson J, Ulfendahl M, Kullander K, Raposo G, Kerje S, Hallböök F, Marks MS, Andersson L. Inactivation of Pmel alters melanosome shape but has only a subtle effect on visible pigmentation. PLoS Genet 2011 Sep;7(9):e1002285.
- Komáromy AM, Rowlan JS, La Croix NC, Mangan BG. Equine Multiple Congenital Ocular Anomalies (MCOA) syndrome in PMEL17 (Silver) mutant ponies: five cases. Vet Ophthalmol 2011 Sep;14(5):313-20.
- Andersson LS, Axelsson J, Dubielzig RR, Lindgren G, Ekesten B. Multiple congenital ocular anomalies in Icelandic horses. BMC Vet Res 2011 May 26;7:21.
- Andersson LS, Lyberg K, Cothran G, Ramsey DT, Juras R, Mikko S, Ekesten B, Ewart S, Lindgren G. Targeted analysis of four breeds narrows equine Multiple Congenital Ocular Anomalies locus to 208 kilobases. Mamm Genome 2011 Jun;22(5-6):353-60.
- Webb AA, Cullen CL. Coat color and coat color pattern-related neurologic and neuro-ophthalmic diseases. Can Vet J 2010 Jun;51(6):653-7.
- Sandmeyer LS, Grahn BH. Diagnostic ophthalmology. Can Vet J 2009 Mar;50(3):319-20.
- Andersson LS, Juras R, Ramsey DT, Eason-Butler J, Ewart S, Cothran G, Lindgren G. Equine Multiple Congenital Ocular Anomalies maps to a 4.9 megabase interval on horse chromosome 6. BMC Genet 2008 Dec 19;9:88.
- Grahn BH, Pinard C, Archer S, Bellone R, Forsyth G, Sandmeyer LS. Congenital ocular anomalies in purebred and crossbred Rocky and Kentucky Mountain horses in Canada. Can Vet J 2008 Jul;49(7):675-81.
- Brunberg E, Andersson L, Cothran G, Sandberg K, Mikko S, Lindgren G. A missense mutation in PMEL17 is associated with the Silver coat color in the horse. BMC Genet 2006 Oct 9;7:46.
Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
