ABSTRACT
ANATOMY AND PHYSIOLOGY INTRODUCTION The lens is a biconvex clear structure located behind the iris in the patellar fossa of the anterior vitreous. It is held in place by the zonules or the tertiary vitreous. While the lens is not the major refractive medium of the eye, its ability to vary in refractive power with accommodation makes it unique. The lens is also unique in its transparency, high protein content, high carbonic anhydrase (CA) levels, high glutathione levels, and lack of vascularity and innervation1, 2. The lens depends on the aqueous humor and vitreous for nutrition and elimination of waste products. The lens is composed of the lens capsule, lens epithelium, and lens fibers, with very minimal intercellular constituents. The lens in the dog is about 10.5 mm in diameter and 7.5 mm in axial thickness, in the cat is 9-10.4 mm in diameter and 7.5 mm in axial thickness, and in the horse is 21 mm in diameter and 12.75 mm in axial thickness3.
