OJVM  Vol.4 No.5 , May 2014
Functional Microvascular Anatomy of the Horse Eye: A Scanning Electron Microscopic Study of Corrosion Casts
Abstract: Objective: This study presents the microvasculature of the horse iris, ciliary process, retina, and choroid and discusses the functional significance of the vasculature. Procedure: Seven horses were used for this study. The ocular vascular system was injected with methylmethacrylate resin via the carotid artery, and the vascular corrosion casts were observed using a scanning electron microscope. Results: The iridial vessels showed a wavy course. The ciliary process was supplied by 2 arterial routes: the iridial and ciliary arterial circles. The subjects displayed a paurangiotic retina with retinal vessels extending only a short distance around the disc. The retinal arterioles and venules ran in closely related pairs, and the capillaries formed hairpin loops. No central retinal artery was seen in the equine eyes examined. The choriocapillaris in the avascular retina was arranged in honeycomb hexagon lobules and formed a more densely packed network than that in the vascular retina. There were 2 distinct venous drainage systems in the horse choroid: the vortex veins and the posterior ciliary veins. The vortex vein ampulla was flattened and showed a slit-like lumen at the merge site with the ophthalmic vein. The vortex veins demonstrated a marked constriction before leaving the eye. Discussion: The 2 choroidal drainage systems may compensate each other in event of occlusion. The ampulla and the constriction in the vortex veins may act as a valve regulating the blood flow to keep the eye at an optimum size and the intraocular pressure within the normal physiological range.
Cite this paper: Ninomiya, H. and Inomata, T. (2014) Functional Microvascular Anatomy of the Horse Eye: A Scanning Electron Microscopic Study of Corrosion Casts. Open Journal of Veterinary Medicine, 4, 91-101. doi: 10.4236/ojvm.2014.45011.

[1]   Anderson, B.G. and Anderson, W.D. (1977) Vasculature of the Equine and Canine Iris. American Journal of Veterinary Research, 38, 1791-1799.

[2]   Smith, P., Samuelson, D. and Brooks, D. (1988) Aqueous Drainage Paths in the Equine Eye: Scanning Electron Microscopy of Corrosion Casts. Journal of Morphology, 198, 33-42.

[3]   De Schaepdrijver, L., Simoens, P., Lauwers, H. and De Geest, J.P. (1989) Retinal Vascular Patterns in Domestic Animals. Research in Veterinary Science, 47, 34-42.

[4]   Simoens, P., Muylle, S. and Lauwers, H. (1996) Anatomy of the Ocular Arteries in the Horse. Equine Veterinary Journal, 28, 360-367.

[5]   Simoens, P., Van den Broeck, W. and Lauwers, H. (2001) Scanning Electron Microscopic Study of the Posterior Ciliary Veins in Domestic Ungulates. Folia Morphologica, 60, 21-26.

[6]   Molleda, J.M., Cervantes, I., Galan, A., Tardon, R., Gallardo, J.M. and Martin-Suarez, E.M. (2008) Fluorangiographic Study of the Ocular Fundus in Normal Horses. Veterinary Ophthalmology, 11, 2-7.

[7]   Morrison, J.C., De Frank, M.P. and Buskirk, M.M. (1987) Comparative Microvascular Anatomy of Mammalian Ciliary Processes. Investigative Ophthalmology & Visual Science, 28, 1325-1340.

[8]   Schoster, J.V. (2006) Normal Fundus and Variations in the Dog, Cat and Horse.

[9]   Funk, R.H. Wagner, W. and Wild, J. (1992) Microendoscopic Observations of the Hemodynamics in the Rabbit Ciliary Processes. Current Eye Research, 11, 543-551.

[10]   Yu, D.Y. and Cringle, S.J. (2001) Oxygen Distribution and Consumption within the Retina in Vascularised and Avascular Retinas and in Animal Models of Retinal Disease. Progress in Retinal and Eye Research, 20, 175-208.

[11]   Snodderly, D.M. and Weinhaus, R.S. (1990) Retinal Vasculature of the Fovea of the Squirrel Monkey, Saimiri sciureus: Three-Dimensional Architecture, Visual Screening, and Relationships to the Neuronal Layers. Journal of Comparative Neurology, 297, 145-163.

[12]   Timney, B. and Macuda, T. (2001) Vision and Hearing in Horses. Journal of American Veterinary Medical Association, 218, 1567-1574.

[13]   McMenamin, P.G. (2007) The Unique Paired Retinal Vascular Pattern in Marsupials: Structural, Functional and Evolutionary Perspectives Based on Observations in a Range of Species. British Journal of Ophthalmology, 91, 1399-1405.

[14]   Walls, G.L. (1939) Notes on the Retinae of Two Opossum Genera. Journal of Morphology, 64, 67-87.

[15]   Craigie, E.H. (1945) The Architecture of the Cerebral Capillary Bed. Biological Review, 146, 20133-20146.

[16]   Chase, J. (1982) The Evolution of Retinal Vascularization in Mammals. A Comparison of Vascular and Avascular Retinae. Ophthalmology, 89, 1518-1525.

[17]   Fautsch, M.P. and Johnson, D.H. (2006) The Second ARVO/Pfizer Research Institute Working Group. Aqueous Humor Outflow: What Do We Know? Where Will It Lead Us? Investigative Ophthalmology & Visual Science, 47, 4181-4187.

[18]   Bhutto, I.A. and Amemiya, T. (2001) Microvascular Architecture of the Rat Choroid: Corrosion Cast Study. Anatomical Record, 264, 63-71.

[19]   Grozdanic, S.D., Betts, D.M., Sakaguchi, D.S., Kwon, Y.H., Kardon, R.H. and Sonea. I.M. (2003) Temporary Elevation of the Intraocular Pressure by Cauterization of Vortex and Episcleral Veins in Rats Causes Functional Deficits in the Retinal and Optic Nerve. Experimental Eye Research, 77, 27-33.

[20]   Wagner, J.A., Edwards, A. and Schuman, J.S. (2004) Characterization of Uveoscleral Outflow Enucleated Porcine Eyes Perfused under Constant Pressure. Investigative Ophthalmology & Visual Science, 45, 3203-3206.

[21]   Wilcock, B.P., Brooks, D. and Latimer, A. (1991) Brief Communications and Case Reports: Glaucoma in Horses. Veterinary Pathology, 28, 74-78.

[22]   Smith, P.J., Samuelson, D.A., Brooks, D.E. and Whitley, R.D. (1986) Unconventional Aqueous Humor Outflow of Microspheres Perfuse into the Equine Eye. American Journal of Veterinary Research, 47, 2445-2453.

[23]   De Geest, J.P., Lauwers, H., Simoens, P. and De Schaepdrijver, L. (1990) The Morphology of the Equine Iridocorneal Angle: A Light and Scanning Electron Microscopic Study. Equine Veterinary Journal, 10, 30-35.

[24]   Samuelson, D., Smith, P. and Brooks, D. (1989) Morphologic Features of the Aqueous Humor Drainage Pathways in Horses. American Journal of Veterinary Research, 50, 720-727.

[25]   Norn, M. (2005) The Glaucoma Theory of CF Heerfordt. Dan Medicinhist Arbog, 33, 103-114.

[26]   Elagouz, M., Stanescu-Segall, D. and Jackson, T.L. (2010) Uveal Effusion Syndrome. Survey of Ophthalmology, 55, 134-145.

[27]   Viana, R., Batourina, E., Huang, H., Dressler, G.R., Kobayashi, A., Behringer, R.R., Ellen Shapiro, E., Hensle, T., Lambert, S. and Mendelsohn, C. (2007) The Development of the Bladder Trigone, the Center of the Anti-Reflux Mechanism. Development, 134, 3763-3769.