ANATOMY
- Situated in the orbital cavity, almost spherical in shape and about 2.5 cm in diameter.
- The space between the eye and the orbital cavity is occupied by fatty tissue. The bony wall of the orbit and the fat helps to protect the eye from injury.
- Structurally the two eyes are separate but they function as a pair. It is possible to see with only one eye, but three-dimensional vision is impaired when only one eye is used to judge distance.
The eyeball has three layers namely:
- The outer fibrous layer—Sclera and cornea
- The middle vascular layer—Iris, ciliary body and choroid
- The inner nervous tissue layer—Retina.
Interior of the Eyeball
The structures inside the eyeball are:
- Aqueous humor
- Lens 3. Vitreous.
Accessory Structures of the Eye
- Eyebrows
- Eyelids and eyelashes
- Lacrimal apparatus
- Extraocular muscles of the eye.
Function of different parts of the eye
Sclera: Tough opaque protective outer layer
Cornea: Same as sclera but transparent to allow transmission of light. Convex shape ➔ refraction of light. Dense connective tissue ➔ maintains its structural integrity, providing protection from mechanical damage and UV rays.
Choroid: Vascular layer supplying retina with nutrients.
Ciliary bodies: Continuation of choroid, attached to iris, adjusting size of the pupils to control the amount of light coming in.
Ciliary processes: secrete aqueous humor into the anterior chamber to nourish and clean the lens and cornea, as well as maintaining intraocular pressure.
Retina: Pigment layer absorbs light and the neural layer acts as a transducer to convert light energy into electrical impulse using cone cells and rod cells.