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What is 20/20 vision?
"20/20 vision" is commonly accepted as the standard of normal distance vision for a human being. Basically it means "good visual acuity at 20 feet." So if your vision is 20/20, you can read certain sizes of letters on a Snellen chart clearly at 20 feet or closer. But if your friend has 20/15 vision, his visual acuity is better than yours: you would have to stand 15 feet away from the chart to read the smaller letters that he can read while standing 20 feet away. Conversely, someone with 20/30 vision has worse distance vision than you.
By the way, visual acuity at a distance isn't the only measure of how good your vision is. You could have 20/20 distance vision but still have difficulty seeing at night because of poor contrast sensitivity. Or you could have near vision problems because you're over 40 and experiencing presbyopia.
The medical term for nearsightedness. Myopia occurs when an eye is too long for the cornea's curvature. As a result, light rays entering the eye do not come to a sharp focus on the retina at the back of the eye. Instead, they focus further forward, producing a blurred image.
See link for more information: http://en.wikipedia.org/wiki/Myopia
The medical term for Farsightedness. Hyperopia occurs when an eye is too short for the cornea's curvature. As a result, light rays entering the eye focus behind the retina instead of precisely on the retina, and a blurred image is produced. A person with hyperopia cannot see distant objects clearly. See link for more information: http://en.wikipedia.org/wiki/Hyperopia
Astigmatism is the result of having a cornea that is irregular in shape. The cornea is normally round. An astigmatic cornea is oblong or "football" shaped, resulting in a condition that generally causes eyestrain, headaches and blurry vision. Astigmatism is often associated with nearsightedness and farsightedness.
See link for more information: http://en.wikipedia.org/wiki/Astigmatism
Presbyopia is a condition in which the focusing ability of a person's eyes has decreased to the point where vision at his reading distance becomes blurred and difficult.
See link for more information: http://en.wikipedia.org/wiki/Presbyopia
Eye health concerns noted:
A Cataract is a clouding or opacity of the natural internal lens of the eye, which causes a visual impairment.
The natural lens is located behind the iris, or "colored part" of the eye. The opacity may be a small dot or may involve the entire lens.
The opacity in the lens causes the light entering the eye to be scattered, causing images to appear hazy or blurred.
See link for more information: http://en.wikipedia.org/wiki/Cataracts
GLAUCOMA OR GLAUCOMA SUSPECT
Glaucoma is an eye disease in which pressure increases in the eye due to clogged or blocked passages. Fluid that normally drains through these passages begins to build up, and the increased pressure can damage the optic nerve. Open-angle glaucoma tends to develop without warning--often painlessly and with no symptoms. Because of this, it can cause damage and blindness more quickly when untreated. Risk factors for developing glaucoma include people over the age of 40; those who have a family history of glaucoma; those who are very nearsighted; diabetics; and African-Americans.
See link for more information: http://en.wikipedia.org/wiki/Glaucoma
The most common symptom of macular degeneration is blurred central vision; noticeably worse when reading. In addition, horizontal lines may appear wavy and/or distorted. The most common method of detecting macular changes is the Amsler Grid test. During an eye examination, you are asked to look at the grid's center dot and asked if you notice any wavy, distorted, missing, or broken lines on the grid. Any one of these irregularities may indicate changes within the macular region of the eye. Your ophthalmologist or optometrist will be able to confirm any suspicions of macular degeneration during a dilated retinal examination.
See link for information: http://en.wikipedia.org/wiki/Macular_Degeneration
DRY EYE DISEASE
There is no known cure for dry eye. However, some dry eye symptoms are caused by medications, eye infections or wearing contact lenses. In these cases, simply eliminating the cause of dry eye will stop the problem. In many cases, however, dry eyes are a lifelong problem. You can relieve the symptoms, but not cure the original cause. Most eye care specialists recommend artificial tear products (ocular lubricants) for their patients with dry eyes. Follow your eye care specialist's recommendations in order to effectively relieve dry eye symptoms and avoid further damage to your eyes.
See link for more information: http://en.wikipedia.org/wiki/Dry_eye_disease
DIABETIC RETINOPATHY OR OTHER DIABETIC ISSUES
Diabetic Retinopathy is condition where a diabetic persons blood sugar gets too high. When this occurs, the high blood sugar level starts a series of events which end in damaged blood vessel walls. Blood vessels in the eye are small and delicate. As such, the blood vessels in the eye are easily damaged. The damaged vessels can then leak fluid or bleed, causing the retina to swell and form deposits known as exudates.
See link for more information: http://en.wikipedia.org/wiki/Diabetic_retinopathy
HYPERTENTION OR OTHER HIGH BLOOD PRESSURE ISSUES
Hypertension, or high blood pressure, is a disease that can have serious effects on many parts of the body, including the eyes. Hypertension causes damage to the tiny and fragile blood vessels that feed the retina.
What can be done? To reduce the risk of hypertensive eye disease, regular examinations by a physician are needed to monitor the condition. Hypertension must be controlled as much as possible and the key to control is to follow the advice of your physician.
See link fore more information: http://en.wikipedia.org/wiki/Ocular_hypertension
If you would like a more detailed explanation of items listed above, please visit the “Eye Cyclopedia” tab of our website.