Structure of the Canine Eye

THE STUCTURE OF THE CANINE EYE
by Jennie Bullock

The canine eye is actually a relay station which collects light images. The eye transforms these images into nervous impulses and then passes them, via the optic nerve, to the brain. Within the brain the impulses are transformed, triggering the perception of sight.
The eye is composed of many complex structures necessary for its proper function. The globe-like eyeball sits within the folds of the eyelids, which protects the globe from foreign materials and retains the lubrication of the eye. The inner surface of the lid is lined with a vascular tissue called the conjunctiva. The conjunctiva forms a pocket at the front of the eye and keeps foreign material from slipping behind the eyeball.
The eye, itself, is made up of three layers. The cornea, which is a transparent layer around the front of the eye, and the sclera, which is a white, dense connective tissue around the back of the eye. These make up the outer layer of the eye. The middle layer of the eye includes: a) the iris, which is the colored portion of the eye, and is composed of blood vessels and muscle fiber which controls the opening and closing of the pupil through which light passes, b) the ciliary body, which contains muscle fibers responsible for alterations of the shape of the lens (it is by the shape changing of the lens that the eye can focus), and c) the choroid, a vascular layer of tissue which lines the sclera and is key in supplying blood flow and nutrients to the structures of the eye. The innermost layer is the retinal layer, which consist of receptor cells, the rods and cones, which collects the light, and transforms the light into neural impulses. The retinal layer relays these impulses to the brain by way of the optic nerve. The lens separates the interior of the eye into two unequal areas. The large area behind the lens, is the posterior compartment, the area is filled with a transparent gelatinous mass called the vitreous humor. The area in front of the lens is divided into a posterior chamber, which is the space between the iris and the lens, and the anterior chamber, which is the space between the iris and the cornea. These two chambers are filled with a transparent watery fluid called the aqueous humor. Light passes first through the cornea and the aqueous humor, it is the pupil which controls the amount of light allowed to pass through to the lens, the lens then focuses the light images which pass through the vitreous humor before reaching the receptor cells of the retina. For a clear interpretation of the image by the brain, all of these structures must be healthy and transparent. Often these structures are affected eirther by environmental or hereditary factors which can either interrupt or interfere with their proper function. The interference can lead to partial or complete vision impairment.

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