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Sight and Vision
Transcript of Sight and Vision
focus images correctly. Photoreceptors 3 main parts - an outer segment that detects light - an inner segment that provides energy for the cell - & a synaptic terminal that transmits the visual signal to the next nerve cell in the pathway leading to the brain *in rods this segment is shaped like rods; in cones it is shaped like cones; this is where the photoreceptors get their names* Photopigment Molecules in the outer segment of the photoreceptors these molecules undergo chemical changes when activated by light different photopigments absorb some light better than others the light that is absorbed best by a photopigment is called its absorption maximum only absorbed light produces the photochemical reaction that results in vision Disorders Glaucoma Astigmatism Farsightedness Cataracts Nearsightedness a disease that causes damage to the optic nerve Glaucoma is a condition of that causes increased pressure within the eyeball this results in gradual loss of sight. At age 50 about 2% of the US population has glaucoma, increasing to 4% by age 70 and 24% for those over age 80 Often times, a person with glaucoma is unaware that they have it, because there are no symptoms. This is one reason it is important to get a dilated eye exam every two years. With early diagnosis there are treatments that can often protect against irreversible damage to the optic nerve. If left undetected Glaucoma can lead to complete loss of vision. Astigmatism is the condition that results from the curvature of the cornea being irregular. Because of the irregular curvature the eye is unable to focus light rays correctly when it reaches the retina. This results in a blurred image at all distances. This condition is normally present at birth, but can form after a person has undergone eye surgery or has had an eye injury. Cataracts are cloudy areas that appear in the lens of the eye which is suppose to be clear Cataracts can develop in one or both eyes. If they develop in both eyes, one will be more severely affected than the other. A normal, clear lens allows light to pass through to the retina where the image is focused. If a part of the lens becomes opaque, light does not pass through easily and the image becomes blurry. A person's vision with Cataracts is similar to a person with perfect vision looking through a glass of cloudy water or through a fogged up window. The more opaque (or cloudy) the lens is, the worse that the patient's vision becomes because more of the light is distorted, People who are farsighted see things at a distance more easily than they see things up close. If you are farsighted, close objects may be so blurry that you can't do tasks such as reading or sewing without glasses. Farsightedness occurs when light entering the eye is focused behind the retina instead of directly on it. This is happens when an eye is too short, the cornea is not curved enough, or the lens sits farther back in the eye than normal. Many times, as we get older, our eye sight weakens, and we lose the ability to focus images properly. This results in farsightedness. Most often, farsightedness begins in childhood, but normal growth corrects the problem. If the child still experiences symptoms after the eye is fully grown, the process of accommodation usually makes up for it. Presbyopia This condition is called Presbyopia. As presbyopia gets worse, near and distance vision will become blurred, until you need glasses or contacts for both. People with nearsightedness have difficulty seeing distant objects, but can clearly see objects that are near. A person who is nearsighted may not be able to make out highway signs until they are just a few feet away. In nearsighted people, the eyeball is too long or the cornea has too much curvature, so the light entering the eye is not focused correctly. Images focus in front of the retina, rather than directly on the retina, causing blurred vision. Nearsightedness runs in families and usually appears in childhood. Usually the condition plateaus, but it can worsen with age. Glasses, contact lenses, or refractive surgery can correct nearsightedness. Nearsighted prescriptions are represented as a negative number (such as -3.00). The higher the number, the stronger the prescription is. The prescription of eye glasses and contact lenses helps the eye focus light on the retina, clearing up the vision. There are also refractive surgeries available that improve the eye's ability to refract the light onto the retina. This would reduce or eliminate a patient's dependency on glasses or contacts.