Light rays pass through the dark center of the eye, called the pupil. The mucous membrane which is called the conjunctiva that lines the eyelids and coats the front portion of the eyeball over the white of the eye. The conjunctiva is very blur and colorless except when blood vessels are dilated. Dust or smoke may cause to dilate the blood vessels and give the conjunctiva an appearance of red which is generally known as bloodshot eyes.
The cornea which is a fibrous, transparent tissue that extends over the pupil and colored eye portion. The cornea works as it bend, or refract, the rays of light; so that they are indented properly on the cells of the sensitive receptor in the region of the eye which is posterior. The cornea is a vascular which has no blood vessels but receives its nourishment from blood vessels near its junction with the white of the eye, the selera. For people with scarred or opaque corneas are successful corneal transplants because the cornea has no supply of blood and rejection of foreign tissue is made with the response of antibodies which do not reach it. The sclera which is a fibrous, tough, supportive, connective tissue that extends from the cornea on the front surface of the eyeball to the nerve which is optic in the back of the eye.
Inside the sclera, there is a dark brown membrane called the choroid. This contains many blood vessels that supply nutrients to the eye. The choroids is continuous with the pigment containing iris and on the anterior surface of the eye called the ciliary body.
The iris which is colored can appear blue, green, gray, hazel or brown portion of the eye that rounds the pupil. The iris constrict the pupil in bright light of the muscles and dilate the pupil in dim light thereby regulating the amount of light entering the eye.
On each side of the lens, the ciliary body contains muscles that can adjust the shape and thickness of the lens. The refraction of light rays in the shape of the lens aid these changes. The lens is thinned or flattened for distant vision and thickened for close vision by the muscles of the ciliary body. This refractive power of the lens is called accommodation.
In the next post we would learn further about the eye’s anatomy and physiology.
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