Recipient Organization
UNIVERSITY OF FLORIDA
G022 MCCARTY HALL
GAINESVILLE,FL 32611
Performing Department
College of Veterinary Medicine
Non Technical Summary
Glaucoma is an eye disease that results from an increase in intraocular pressure caused from a build up of aqueous humor, with the end consequence of optic nerve damage and severe vision impairment. In the normal eye, aqueous humor is secreted by the ciliary body to the posterior chamber, through the pupil to the anterior chamber, and then exits the eye at the iridocorneal angle. Located in the iridocorneal angle is the trabecular meshwork, which is tissue that drains the aqueous fluid from the anterior chamber into specific tubes called "Schlemm's canal", which then delivers this fluid into the bloodstream. Problems within this current of aqueous humor will result in the fluid not being drained correctly, eventually leading to the occurrence of glaucoma. Secondary glaucoma is when this disease is caused by infection or inflammation, and one example of this is the inflammation of the corneal endothelial cells. This inflammation, or endotheliitis, produces vertical corneal edema, which can end up changing the aqueous humor flow and leading to the increased intraocular pressure, and then glaucoma. An explanation for how these changes occur is that there are regional differences in the iridocorneal angle between the dorsal/ventral and nasal/temporal regions, so when the endothelial cells become irritated, alterations in the current occur at these localized areas and the edema will form. In this study, the characteristics of the microanatomy of the iridocorneal angle will be examined and the trabecular meshwork of each of these regions will be compared with a computer to determine ift differences exist, and how these differences affect the aqueous humor drainage in the eye. Differences in the amount of "space" that occurs within the trabecular meshworks between these different regions could be one of the main effecting factors that leads to the aqueous humor buildup when endotheliitis occurs. Less space means more aqueous humor turbulence to damage endothelial cells and cause water or edema to occur in the cornea.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The most common risk factor for glaucoma in the horse is iridocyclitis. Chronic inflammation can lead to eventual obstruction of the iridocorneal angle (ICA). Abnormal formation of the ICA could exacerbate the tendency for glaucoma to occur in horses with iridocyclitis. The pattern of vertical corneal edema found in endotheliitis may represent an earlier stage of glaucoma, and may represent a unique clinical sign, disease process or both. Disease of the horse corneal endothelial cells or endotheliopathy results in generalized or regional corneal edema depending on the cause of the endothelial disease. Edema in the ventral quadrant is found with iridocyclitis due to dysfunction of the ventral endothelial cells, while an anterior lens luxation can cause central or generalized corneal edema due to physical contact with endothelial cells in the respective regions. Endotheliitis or inflammation of the corneal endothelial cells has recently been noticed with vertical corneal edema. Aqueous humor normally moves dorsally adjacent to the warm vascular iris, and then flows ventrally against the cooler corneal endothelium.(Adler p 229) Alterations in the aqueous humor current sufficient to cause this vertical central pattern of edema appears to be a prerequisite for, and preceeds, elevated IOP in a very aggressive form of glaucoma in the horse. The localized vertical edema found in these horses suggests that alterations in aqueous humor convections currents may be involved in the pattern of corneal edema and the elevation of IOP. Disturbance of the normal fluidic movement of aqueous humor outflow due to microanatomic differences in the preglaucomatous dorsal/ventral versus nasal/temporal ICA may cause turbulence that physically irritates and alters the function of the endothelial cells such that the pattern of vertical edema occurs. The clinical appearance of the dorsal/ventral equine ICA differs from the appearance of the nasal/temporal equine ICA. We suggest that regional differences in the microanatomy of the equine ICA may contribute to abnormalities in the flow of aqueous humor to result in fluidic turbulence that causes vertical corneal edema and subsequent glaucoma in horse eyes without iridocyclitis. Morphologic features of the ICA of the normal horse will be examined for regional differences in microanatomy. We hypothesize that regional anatomical differences in the microanatomy of the equine iridocorneal angle (ICA) are associated with specific patterns of vertical corneal edema and subsequent elevations in intraocular pressure (IOP) in the early stages of certain forms of immune-mediated corneal endothelial disease. Specifically, the dorsal/ventral region of the equine iridocorneal angle differs in the amount of trabecular meshwork available for aqueous humor drainage compared to the nasal/temporal portion of the iridocorneal angle.
Project Methods
Tissue preparation: Clinically normal horse eyes will be immediately fixed in 2 percent glutaraldehyde cadodylate buffered solution after euthanasia not related to this project. The globe and entire cornea and limbus were removed post-euthanasia, and specimens of the tissue from the dorsal, ventral, nasal and temporal quadrants will be isolated, and placed in fixative at 4C. The tissues are then further fixed in 1 percent osmium tetroxide for 1 hour at 22C, washed, dehydrated, and flat embedded in Epon-Araldite mixture. One micron sections will be stained with toluidine blue for light microscopy. Some eyes will be fixed in buffered 10% formalin, cut into quarters, embedded in paraffin, and stained with haemotoxylin and eosin. Light microscopy and image digitalization The videodensitometry system was designed around an Optiphot-Pol polarizing light microscope (Nikon). Light is transmitted through a x 10 objective and a xl ITV relay lens to a solid-state CCD videocamera (series 4810, Cohu, San Diego, California) mounted on the eyepiece tube. Resolution of the camera is 754 (horizontal) X 488 (vertical) photosites. Images is digitized by a videoframe grabber (PCVISION plus, Imaging Technology, Woburn, Massachusetts) at a resolution of 640 (horizontal) x 480 (vertical) pixels with eight-bit pixels (256 gray levels). Pixel size was 1.82 square microns. Digitized images will be displayed on a high-resolution onitor (model C-3479, Mitsubishi, Torrance, California) and captured to a computer as Jpeg files. Image analysis A computerized image analysis system (MCID M1 System: Imaging Research Inc., St Catharines, Ontario, Canada) will be used to analyze digitized light microscopic photographs of each horse ICA. Four ICA regions, designated as dorsal (D), temporal (T), nasal (N), and ventral (V) will be measured for total intrameshwork scan area (mm2). The photographic slides will be placed on a camera Statistical comparison Observations on eight normal horse eyes will consist of individual meshwork cross-sectional areas (D, T, N, V) of the angle. Repeated measures analysis of variance (ANOVA), with section (DN, DT, VN, VT) considered as a four-level within-subject factor will be used to test for statistically significant differences in mean response among sections and among combinations of sections combined by averaging within animal.