Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

The Sense of Vision (Eye)The eye is set in a bony socket, the orbit. The visible portion of the eye is covered by a thintransparent membrane called the coniunctiva 1.The eyeball is not a solid sphere. It contains a large interior cavity that is divided into two parts,the anterior and posterior cavities. The anterior cavity, in turn, has two subdivisions known as theanterior chamber and the posterior chamber. Most of the eyeball (Figure 76) is recessed in the orbit,protected by the walls of this bony cavity. The wall of the eyeball is composed of three layers; fromthe outside to the inside, they are the sclera, the choroid, and the retina.. The sclera, composed of tough fibrous tissue, is the protective and supportive layer of theeye. The anterior portion of the sclera, called the cornea, lies over the colored part of theeye (iris) and the pupil. The cornea is transparent and allows passage of light.o The middle or choroid layer (the pigmented vascular coat) of the eye contains a great manyblood vessels. The iris, the colored muscular ring, controls the size of the pupil and theamount of light entering the eye. The anterior portion is modified to form the ciliary body,the main part of which is ciliary muscle. Its function is the adjustment of the lens of theeye for vision at different distances. The crystalline lens is suspended from the innersurface of the ciliary body by circular ligaments called the suspensory ligaments. Thefunction of the lens is to bend light rays in order to focus an image on the retina.° The retina is the innermost layer of the eye. It is composed of two sections: the outer ispigmented and attached to the choroid layer, and the inner is composed of nervous tissue.The retina is the light sensitive layer.Figure 75. EYEPog ter Lot chamber................ v,,,-,,.,,, boa,Eye muscle Choro i.dlconjunctiva--mucous membrane covering the anterior portion of the eyeball, and lining theeyelids.415