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Vision tests check many different functions of the eye. Some of the tests measure your ability to see details at near and far distances, check for gaps or defects in your field of vision, and evaluate your ability to see different colours. Others may check how sensitive you are to glare (brightness acuity), how well your eyes work together to provide depth perception, and more. Vision tests are usually done along with examinations and tests that check the health of the eye. Here are some common tests that check for blurred or low vision.
These tests may be done:
This test is done:
These may be done:
If you wear glasses or contact lenses, bring them with you to the examination since the tests cannot be properly performed without them. If you have a copy of your current eyeglass prescription, bring it with you.
If you have a young child, it is best to practice eye tests at home before you take your child to the appointment. This can help your child co-operate better during the real testing. For more information, see the topic Pediatric Preparation for Medical Tests.
Many medicines may affect the results of vision tests. Be sure to tell your doctor about all the over-the-counter and prescription medicines you take.
Talk to your doctor about any concerns you have regarding the need for vision tests, how they will be done, or what the results will mean. To help you understand the importance of these tests, fill out the medical test information form .
Visual acuity tests are used to evaluate eyesight. Several types of visual acuity tests may be used.
If you cannot read any of the letters or print on these charts because of poor vision, your visual acuity will be tested by other techniques, such as counting fingers, detecting hand movements, or distinguishing the direction or perception of light sources (such as room light or a penlight held up close to the face).
Visual acuity tests usually take about 5 to 10 minutes. They may be performed by a nurse, a medical assistant, an ophthalmologist, an optometrist, a teacher, or some other trained person. Testing may be done at a doctor's office, school, workplace, health fair, or elsewhere.
Refraction is a test that measures the eye's need for a corrective lens (refractive error). For this test, you will be asked to describe the effects of looking at an eye chart through various corrective lenses.
Your doctor may use eyedrops to widen (dilate) your pupils before you start this test. The eyedrops take about 15 to 20 minutes to dilate the pupil fully.
The doctor may put a device (called a phoropter) in front of your eyes. The device contains many different lenses. Testing one eye at a time, the doctor will ask you to compare the effects of two lenses (first one lens, then the other). You should state which lens of each pair gives you better vision. The doctor will continue to test your eyes with different lenses until it is determined which lenses correct your vision the best. Your doctor may use a hand-held device (retinoscope) to shine light into your eyes. A series of trial lenses will be placed in front of your eyes and adjusted until the light rays are properly focused on your retina.
Visual field tests are used to check for gaps in your range of vision. They can help detect eye diseases or nervous system problems that limit your ability to see objects clearly in the entire visual field or in one part of it. Several tests are commonly done to evaluate a person's visual field.
Colour vision tests check your ability to distinguish colours. In the most commonly used colour vision test, you look for different coloured numbers or symbols hidden in varying backgrounds of coloured dots.
First, you are shown sample patterns and told what symbols and numbers you can expect to see. You then sit at a table and cover one eye. The doctor holds the colour test patterns about 35 cm (14 in.) away from you. Some patterns are harder to pick out than others. As the doctor holds up a pattern, you will identify the number or symbol you see and trace it using a pointer. Some patterns may not have a number or symbol. The test is then repeated with the other eye.
You should not feel any discomfort during these vision tests.
Dilating drops may make your eyes sting and cause a medicine taste in your mouth. You will have trouble focusing your eyes for up to 12 hours after your eyes have been dilated. Your distance vision usually is not affected as much as your near vision, though your eyes may be very sensitive to light. Do not drive for several hours after your eyes have been dilated, unless your doctor says it is okay. Wearing sunglasses may make you more comfortable until the effect of the drops wears off.
In some people, the dilating eyedrops can cause an allergic reaction.
Vision tests check many different functions of the eye. Your doctor will let you know if your eyesight is normal or if it is better or worse than normal. He or she may also be able to tell you why you have a vision problem.
The visual acuity score compares your distance vision with that of people who have normal vision, using an eye chart. Each eye's score is expressed as two numbers, such as 20/20 (6/6) or 20/100 (6/30). The first number is the distance you stand from the chart, usually 20 ft (6 m) when using a typical wall chart. The second number is the distance from which people with normal eyesight can read the same line on the eye chart.
20/20 (6/6) vision is considered normal. A person with 20/20 vision can see at 20 ft (6 m) what people with normal vision can see at this distance.
Your doctor will also tell you if you have reduced near vision.
The doctor tests your eyes with different lenses until the lens that corrects your vision the best (sometimes better than 20/20 or 6/6) is found. The result of a refraction test determines your prescription eyeglass or contact lens strength.
Normally, a person's visual field forms a rough circle with a natural blind spot. If your vision is normal, you should be able to see objects clearly throughout the entire visual field except for the area with the natural blind spot. When you are using both eyes to see, the blind spots do not interfere with your vision.
You may have vision loss in certain areas of the visual field if you are not able to see:
Abnormal results during Amsler grid testing include:
Gaps in different parts of the visual field may have many causes, including eye diseases (such as glaucoma and macular degeneration) or nervous system problems (such as stroke). If results on any of the visual field tests are abnormal, you will need further tests to determine the cause.
People who have normal colour vision are able to distinguish the coloured numbers, symbols, or paths from the background of coloured dots.
If you are not able to distinguish some or all of the coloured patterns from the background, you may have a colour vision problem. You may be able to pick out some patterns of colours but not others. Or you may be able to pick out patterns that are different from a person with normal vision, depending on what type of colour vision problem you have.
Many conditions can change your vision test results. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.
Reasons you may not be able to have the test or why the results may not be helpful include:
Other Works ConsultedChang DF (2011). Ophthalmologic examinations. In P Riordan-Eva, ET Cunningham, eds., Vaughan and Asbury's General Ophthalmology, 18th ed., pp. 27–57. New York: McGraw-Hill.Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Current as of: August 31, 2020
Author: Healthwise StaffMedical Review: Kathleen Romito MD - Family MedicineAnne C. Poinier MD - Internal MedicineAdam Husney MD - Family MedicineE. Gregory Thompson MD - Internal MedicineChristopher J. Rudnisky MD, MPH, FRCSC - Ophthalmology
Current as of: August 31, 2020
Author: Healthwise Staff
Medical Review:Kathleen Romito MD - Family Medicine & Anne C. Poinier MD - Internal Medicine & Adam Husney MD - Family Medicine & E. Gregory Thompson MD - Internal Medicine & Christopher J. Rudnisky MD, MPH, FRCSC - Ophthalmology
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