WHAT EXACTLY IS 20/20 VISION?

Apr 15, 2018 Dr Karen Persram, Features / Columnists

Most people are familiar with the eye chart, either from the doctor’s office or the optometrist’s office. The Snellen eye chart is the most common. It was developed by Dr. Herman Snellen. The chart allows us to define and measure standard vision. It is made up of several rows of letters with the largest (usually an E) at the top and the others having letters that decrease in size. 20/20 is a term used to define “‘normal” vision, based on seeing a certain size image at 20 feet.
That translates in numbers to the 20/20 letters being 8.75 mm high. If you have 20/20 vision, from 20 feet away, you can see clearly 8.75 mm high letters that make up the 20/20 line. If you have 20/30 vision, it means that you must go as close as 20 feet to see a size letter that a person with normal vision can see from 30 feet back.
DO MOST PEOPLE HAVE 20/20 VISION?
Many people see well and assume they have good vision. They are sometimes surprised when they come for their first eye exam and realize this is not always the case. Persons who have never had their eyes checked may not realize that their vision is not as good as it should be because it is how they have always been seeing and assumed was normal. People are also surprised when they find out the vision in each eye may be different. It is not until one eye is covered and the vision checked in each eye individually that some people realize that one eye may be seeing better than the other.
Many people do not have 20/20 vision. Some of the reasons are:
1) Myopia, or nearsightedness, is where near objects are seen clearly, but far objects are not. A sign of nearsightedness is difficulty seeing distant objects like a TV screen or blackboard.
2) Hyperopia, or farsightedness, is where distant objects are seen clearly, but close ones are not. Common signs of farsightedness include difficulty in concentrating and keeping a clear focus on near objects like phone screens, eye strain, fatigue, headaches after close work / reading, or aching or burning eyes.
3) Astigmatism is a vision condition that occurs when the front surface of your eye, the cornea, is slightly irregular in shape. Think of it being egg shaped instead of round like a ball. This irregular shape prevents light from focusing properly on the back of your eye, the retina. As a result, vision may be blurred at all distances. Most people have some amount of astigmatism.
4) Cataracts are a condition where the lens in the eye becomes cloudy with age. The light does not go through the cloudy lens as well as it used to through the clear lens
5) Turned or crossed eyes can lead to decreased vision in the eye that turns.
6) “Lazy” eyes, or amblyopic eyes, which usually occur from not getting glasses early enough, or high prescriptions or uncorrected astigmatism.
An optometric examination will include testing for all forms of visual impairment. If needed, your optometrist can prescribe eyeglasses or contact lenses to change the way the light enters your eyes and to focus the images on the retina. Glasses do not correct your eyes, nor do they make your eyes worse or dependant on them …. they just help you to see better.
For more information, or if you wish to suggest a question, please contact Dr. Karen Persram at 295 Quamina Street, Georgetown. Tel: 225-0605 or send emails to drkpoffice@gmail.com.

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