Vision Tests

Color Vision Tests

Results

Vision tests check many different functions of the eye.

Visual acuity testing

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.

• When the second number is smaller than the first number, the person's vision is better than normal. For instance, a person with 20/10 (6/3) vision can see from 20 ft (6 m) what people with normal vision can see from 10 ft (3 m).
• When the second number is larger than the first number, the person's distance vision is worse than normal.
• A person with 20/200 (6/60) vision or less in his or her best eye when wearing corrective lenses is considered legally blind.

For near vision, 14/14 (35/35) is normal, with 14 in (36 cm) being the normal distance for reading. If the second number is greater than 14 (14/20, for example, or 35/50), it means that you have reduced near vision. You have to be 14 in (36 cm) away to read print that people with normal near vision can read from 20 in (51 cm).

A Jaeger (J) number is another way to rate your near vision. The J number relates to the size of text you could read on the Jaeger chart. The J number goes up as the print size of the text you read goes up. The higher the J number, the worse your near vision. The number can range from J1 to J16. For example:

• J1 means that you could read the smallest text on the chart and that you have 20/15 vision.
• J2 means the line of text you were able to read had larger print than J1, and your vision is 20/20.
• J3 means the line of text you were able to read had larger print than J1 and J2, and your vision is 20/40.

Visual acuity tests usually take about 5 to 10 minutes.

Refraction

The health professional 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.

A refraction test takes 5 to 30 minutes (30 minutes if dilating drops are used).

Visual field test

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:

• Test objects during tangent screen testing.
• Movements or light flashes during perimetry testing.

Abnormal results during Amsler grid testing include:

• Not being able to see the black dot at the center of the grid.
• Not being able to see all four edges of the grid.
• Having blank spots or dark spots on the grid (other than the black dot at the center).
• Seeing lines that look wavy or curved.

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.

Confrontation tests and Amsler grid tests take just a few minutes. More thorough visual field testing that uses perimetry and tangent screens can take more than 45 minutes when both eyes are tested.

Color vision test

People who have normal color vision are able to distinguish the colored numbers, symbols, or paths from the background of colored dots.

If you are not able to distinguish some or all of the colored patterns from the background, you may have a color vision problem. You may be able to pick out some patterns of colors 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 color vision problem you have.

This test takes only a few minutes.

Many conditions can change your vision test results. Your health professional will discuss any significant abnormal results with you in relation to your symptoms and past health.

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Author:	Debby Golonka, MPH	Last Updated: June 18, 2009
Medical Review:	Kathleen Romito, MD - Family Medicine Christopher J. Rudnisky, MD, FRCSC - Ophthalmology
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