The human eye provides us with the ability to visualize the world around us. Light enters the eye through the cornea and excites special neurons on the retina. The brain receives this information and interprets it so that we are aware of what we are seeing. The parts of the eye contribute to its proper function.
Conjunctiva
The conjunctiva is a thin membrane that covers most of the visible surface of the eyeball and the inner surfaces of the eyelids. It is transparent and secretes a film of mucous that keeps the eye moist.
Cornea and Sclera
The cornea and sclera are the two parts of the outermost layer of the eye, known as the tunica fibrosa. The sclera appears white and contains blood vessels, while the cornea is transparent to allow light into the eye.
Lens
The lens of the eye helps to focus light entering the eye. It is held in place by a suspensory ligament and the ciliary body.
Tunica Vasculosa
The middle layer of tissue in the eyeball is called the tunica vasculosa, or uvea. It has three important components: the ciliary body, choroid and iris. The ciliary body is a ring of tissue that supports the lens and iris. It also secretes a fluid called aqueous humor. The iris is the colored part of the eye. It expands and contracts to control the amount of light coming into the eye through they pupil--an opening in the center of the iris. Finally, the choroid is a dark vascular layer of tissue behind the retina that absorbs excess light.
Vitreous Humor
Vitreous humor is a thick jelly-like substance found inside of the eyeball behind the lens. It gives the eyeball its spherical shape and prevents it from collapsing on itself. It also functions to hold the retina in place.
Retina
The retina is a layer of neural tissue outgrowth from the brain. It is spread out like a blanket on the interior surface of the back of the eyeball. It is physically attached to the eye in two places: the optic disc and the ora serrata. The vitreous humor keeps it pressed smoothly against the eye. The retina has special photoreceptor cells called rods and cones that are excited by incoming light. These cells are most concentrated at the macula lutea.
Optic Disc
The optic nerve exits the eye at an area called the optic disc. This area lacks photoreceptor cells, which results in a blind spot in the visual field of each eye. The eye's blood supply also enters and exits the eye through the optic disc.
References
- "Anatomy and Physiology: The Unity of Form and Function (5th Edition)"; Ken Saladin; 2010
- All About Vision: Human Eye Anatomy
- Macula.org: Anatomy of the Eye
