Eye and Its Function

Eye Structure:

Cornea - A clear, dome-shaped window in the very front of the eye. It acts as a window for light to pass in.

Sclera – The sclera is what is known as the “white” of the eye. It serves as the eye’s protective coat.

Lens – The lens is a crystalline structure that focuses light into the retina. In a healthy eye, the lens changes shape to adjust for close or distance vision. Aging will cause the lens to harden and therefore, limit its adjusting power.

Aqueous and Vitreous – The aqueous is located in between the cornea and the lens and is a very thin fluid. It gives the front of the eye its shape as well as nourishes the cornea and lens. The Vitreous is a thicker substance that gives the inner eye it essential shape. With age, it thins and can cause damage to the retina.

Retina – The retina is the sensory tissue that lines the inner layer of the eye, and converts light rays into electrical impulses that communicate with the brain. It is made up millions of photoreceptors known as rods and cones. (For More Information, See Retina page).

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Structure of the eye



Normal physiological vision is created when light waves come in contact with the rods and cones on the outer surface of the retina. This induces photochemical transduction in the form of an electrical impulse which is then sent through the bipolar cells (Alfaro). These cells then relay the electrical message directly or indirectly through amacrine cells to the ganglion cells. All of axons of the ganglion cell come together to form what is known as the optic nerve. Then the signal reaches the optic chiasm and is sent down the optic tract. At a point, the signal turns into optic radiation, and proceeds to the primary visual cortex of the occipital lobe (Alfaro). From there, the message is sent to other processing and association areas of the brain.

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Visual pathway in the brain

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BMES 212
Summer Term 2007
School of Biomedical Engineering, Science and Health Systems