Why Do Doctors Use Eye Charts For Eye Examination?

A standard ophthalmic exam is a comprehensive series of tests done by an ophthalmologist or optometrist. These doctors specialize in eye health. They’ll use these tests to check both your vision and the health of your eyes. A standard ophthalmic exam is also known as a comprehensive eye examination or a routine eye exam.

An eye examination is conducted to examine all the parts of the eyes thoroughly. If any part of the eye is disturbed or has an issue, immediate actions are taken to cure it. During an eye exam, your doctor will place an eye chart in front of you.

The most common eye chart which is used for an eye examination is the Snellen eye chart developed by a Dutch eye doctor named Hermann Snellen in the 1860s. This eye chart consists of 11 rows of capital letters. The first row consists of one single letter, mostly E. Then as you go down, the number of letters increases, and the size of all the letters gradually decreases.

This eye chart is used to determine your vision problem. If you have trouble reading the letters the doctor will place certain lenses in front of your eyes and will ask you to read the chart again. He will keep changing the lenses until you get a clear and 20/20 vision by using those lenses.

What does 20/20 Vision Mean?

20/20 vision is considered a normal vision which means you are able to see things clearly at a distance of 20 feet. Most people are born with 20/20 vision but later get affected by several reasons like cataract, glaucoma, or an eye injury.

Visual Acuity

20/20 vision is a term used to express normal visual acuity (the clarity or sharpness of vision) measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.

Having 20/20 vision does not necessarily mean you have perfect vision. 20/20 vision only indicates the sharpness or clarity of vision at a distance. Other important vision skills, including peripheral awareness or side vision, eye coordination, depth perception, focusing ability and colour vision, contribute to your overall visual ability.

Some people can see well at a distance but are unable to bring nearer objects into focus. This condition can be caused by hyperopia (farsightedness) or presbyopia (loss of focusing ability). Others can see items that are close but cannot see those far away. This condition may be caused by myopia (nearsightedness).

Tumbling “E” Eye Charts

The Tumbling E eye chart can detect nearsightedness in young children who don’t yet know all letters of the alphabet. It’s also
a good “game” to play with a child who might be apprehensive about his or her first eye exam.
Tumbling E eye charts also are useful to test the distance visual acuity of children or adults who cannot communicate verbally due to a physical or mental disability, language barrier, or other reasons.

In these eye charts, only the letter E is used but the direction of the letter changes as you read it. So that person reading the eye chart needs to point out the direction of the letter. They are generally, asked to use their arms or index fingers to point out the direction. The direction can be left, right, up, or down.

According to researches and studies, it is proved that the visual acuity test conducted by using a tumbling ‘E’ chart gives virtually the same result as those obtained from testing with Snellen’s eye chart.

Dilated Eye Exam

A dilated eye examination lets your eye doctor see the back of your eye (retina). It’s usually done as part of a regular eye examination.

Your doctor will use eye drops to widen (dilate) your pupils. This makes it easier to see the back of the eye. Your doctor may also use eye drops to numb the surface of your eyes. It takes about 15 to 20 minutes to fully dilate the pupils. The dilating eye drops may make your eyes sting.

They may also cause a medicine taste in your mouth. When your pupils are dilated, your doctor will shine a bright light into your eyes and examine them. Tell your doctor if you or anyone in your family has glaucoma and if you are allergic to any type of eyedrops. Your vision will be blurry for several hours.

Everyone with diabetes should have regular dilated eye examinations. Diabetes can lead to eye problems that cause vision loss or blindness. The longer you have diabetes, the more likely you will have eye problems. By the time you notice any vision problems, your eyes may already be seriously damaged. A thorough examination can help detect symptoms early. Early treatment may help protect your vision.

Limitations of An Eye Exam

The eye chart is used to measure visual acuity only. They help the doctor to figure out the power of the lens required by your eyes. It also helps them to determine whether you should use eyeglasses or a contact lens. If you have a very poor vision i.e. 20/200 you might not be allowed to drive vehicles as it increases the chances of accidents.

Therefore, after the eye test has been conducted your doctor will briefly tell you about all the Do’s and Don’ts that you should keep in mind to keep yourself away from any harm. 

Eye charts do not measure your colour perception, depth perception, or peripheral vision. It also doesn’t even help in finding out about any eye disease such as glaucoma or the pressure caused by it. It also doesn’t examine the dryness of your eyes or the retina whether it is in good shape or not.

Therefore, the eye chart used for an eye examination is just a component of a complete eye exam. You cannot fully rely on it as there might be other reasons for the trouble faced by your eye. Make sure if your eye problem is not been treated after wearing an eyeglass or contact lens, consult your doctor immediately. Do go for regular check-ups at least once a year.

Overview

An eye chart is used for conducting eye examination. It mainly helps in determining the visual acuity of a person. It consists of several letters which gradually decreases as you go down. For those who are not able to read there is a special eye chart known as tumbling ‘E’ eye chart in which different directions of the same letter are used.

In such eye charts, the patient needs to point out the direction of the letter. Both the eye chart gives approximately the same results. However, the eye chart test has certain limitations and you cannot fully rely on it to determine the cause of your eye problem.

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