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Libby, Mt 59923
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Diagram of the Eye

human eye diagram
Vitreous Gel (also called vitreous humor): A thick, clear gel-like fluid that fills the inside of the eye behind the lens and helps the eyeball maintain its shape. Two common eye conditions associated with the vitreous gel are floaters and flashes. Floaters are tiny clumps of debris or cells inside the vitreous moving in your field of vision. While these objects look like they are in front of your eye, they are actually floating inside. What you see are the shadows they cast on the retina. When the vitreous gel inside your eye rubs or pulls on the retina, you may see what closely resembles flashing lights or lightning streaks. Both floaters and flashes are usually harmless; however, if you notice any new or sudden increase in either symptom, you should consult with your eye physician because of the possibility of a torn retina.
Optic Nerve: The optic nerve, also called cranial nerve II, is a bundle of more than one million nerve fibers that carries visual messages from the retina to the brain. The optic nerve is associated with a number of diseases which typically causes permanent and potentially severe loss of vision. Examples of such diseases are glaucoma, optic atrophy, or optic neuritis caused by multiple sclerosis, viral infections, bacterial infections, diabetes, or a number of other conditions.

The beginning of the optic nerve is called the optic nerve head or optic disc. Because of the lack of photoreceptors, this area of the retina cannot respond to light stimulation. As a result, everybody has what is known as the blind spot in each eye. To experience this interesting phenomenon, visit this link: Your Blind Spot.
Macula: The small sensitive area in the center of the retina situated near the optic nerve that is responsible for central vision. The macula allows us to perform detailed tasks that require central vision such as reading or sewing. Damage to the macula, commonly known as macular degeneration, eventually results in central vision loss making reading or intricate work difficult or impossible without the use of special low vision optical aids.
Fovea Centralis (fovia, or fovea): The center of the macular region of the retina that gives the sharpest central vision which is necessary for reading, watching television, driving, or any activity where visual detail is of primary importance.
Retina: The light-sensitive tissue lining the inner surface at the back of the eye. The retina converts light into electrical impulses that are sent to various visual centers of the brain through the optic nerve. A common problem related to the retina is retinal detachment. Retinal detachment occurs when the retina is pulled away from its normal position in the back of the eye allowing vitreous humor to leak under the thin tissue of the retina. When this occurs, vision is blurred and almost always causes some vision loss or blindness unless it is treated.
Iris: The iris is a membrane in the eye responsible for controlling the diameter and size of the pupil and regulates the amount of light entering the eye. In response to the amount of light entering the eye, muscles of the iris expand or contract the pupil. The larger the pupil, the more light can enter. The color of the iris, or eye color, can be green, blue, brown, hazel, gray, or amber. The common theory is that brown eyes are dominant and blue eyes are recessive when determining eye color. However, that is not necessarily the case. Eye color is determined by multiple genes that are inherited by each parent. The gene that has the greatest effect on eye color is the OCA2 gene because of its ability to control the amount of pigment called melanin that is produced. With two major genes determining the color and minor genes determining variation, the child’s eye color has numerous possibilities including having a completely different eye color than either parent. Oddly enough, when children are first born, they usually have blue eyes because of the small amount of melanin the eye contains. However, melanin production generally increases during the first year of a baby’s life because of light stimulation and the child’s permanent eye color is usually determined by the age of three.
Cornea: The clear front part of the eye that covers the iris, the pupil, and the anterior chamber. Because of its transparency, the cornea does not have blood vessels or a direct blood supply; therefore, it must exchange its nutrients and waste products through its front and back surfaces. The occurrences of corneal ulcers or keratitis are due to invasion by bacteria, fungi or viruses causing infection and inflammation. This condition may cause severe pain and reduce visual clarity and are commonly treated with anti-bacterial or anti-fungal eye drops.
Pupil: The round opening located in the center of the iris of the eye. The muscular action of the iris adjusts the size of the pupil and controls the amount of light that can enter the eye. The round pupil appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. Without any known cause, a small percent of the population has naturally unequal-sized pupils. However, causes of unequal pupil size could include conditions such as glaucoma, head, neck, or eye trauma, or possibly an intracranial tumor, that would require immediate medical attention or require for you to seek the advice of an eye professional.
Lens: A clear structure of the eye located behind the iris that helps focus light or an image on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp image of the object to be formed on the retina. Vision-threatening complications of the lens could include cataracts. A cataract is a clouding that develops in the lens of the eye, varying in degree from slight to complete obstruction of the passage of light. Cataracts typically progress slowly and are a natural process to aging.
Sclera: The tough, white outer coating of the eye that serves as the eye’s protection, also known as "the white of the eye". Six tiny muscles connect to it around the eye and control the eyes movements.
Thank you to the National Eye Institute for the use of this diagram. Visit their site at the National Eye Institute.
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