Eye Anatomy
Read below for a basic description and explanation of the structure of your eyes and how they function to help you see clearly and interact with your world.
Conjunctiva:
The conjunctiva is the thin, clear tissue that covers the outer surface of the eye. It begins at the outer edge of the cornea, covering the visible part of the sclera, and lining the inside of the eyelids. It is nourished by tiny blood vessels. The conjunctiva secretes oils and mucous that moisten and lubricate the eye.
Cornea:
The cornea is the transparent, dome-shaped window covering the front of the eye. It is a powerful refracting surface, providing 2/3 of the eye’s focusing power. It is a clear and shiny structure because there are no blood vessels in a healthy cornea. The cornea has the most nerve endings in the body, making it very sensitive. The adult cornea is about 1/2 millimeter thick. There are five layers: epithelium, Bowman’s membrane, stroma, Descemet’s membrane and the endothelium.
The Crystalline Lens:
The crystalline lens is located just behind the iris. Its purpose is to focus light onto the retina. In young people, the lens changes shape to adjust for close or distance vision. This is called accommodation. As we age the crystalline lens hardens reducing its ability to to accommodate and focus at near. Cataracts are the clouding of this lens.
Iris:
The coloured part of the eye is called the iris. It controls how much light will enter the eye. The black round opening in the center of the iris is called the pupil. The iris is embedded with tiny muscles that dilate and constrict the pupil size.
Retina and Macula:
The retina is a multi-layered sensory tissue that lines the back of the eye. It contains millions of photoreceptors that capture light rays and convert them into electrical impulses. These impulses travel along the optic nerve to the brain where they are turned into images.
The macula is located roughly in the centre of the retina, temporal to the optic nerve. It is a small and highly sensitive part of the retina responsible for detailed central vision. The fovea is the very center of the macula.
Pupil:
The pupil is the opening in the center of the iris. The size of the pupil determines
the amount of light that enters the eye. The pupil size is controlled by the muscles of the iris.
Optic Nerve:
The optic nerve transmits electrical impulses from the retina to the brain. It connects to the back of the eye near the macula. When examining the back of the eye, a portion of the optic nerve called the optic disc can be seen. The retina’s sensory receptor cells of the retina are absent from the optic nerve. Because of this, everyone has a normal blind spot.
Sclera:
The sclera is commonly known as “the white of the eye.” It is the tough, opaque tissue that serves as the eye’s protective outer coat. Six tiny muscles connect to it around the eye and control the eye’s movements. The optic nerve is attached to the sclera at the very back of the eye.
Viterous:
The vitreous is a thick, transparent substance that fills the center of the eye. It gives the eye form and shape. The vitreous is firmly attached to certain areas of the retina. With time, the vitreous shrinks and shrivels, causing shadow like images called floaters.
References:
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OSI Expand Your Eye-Q Module 1:Basic Optics Workbook 1:Anatomy of the Eye
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http://health.howstuffworks.com/human-body/systems/eye/eye1.htm