Vision Tests

Color Vision Tests

Results

Vision tests check many different functions of the eye.

Visual acuity testing

The visual acuity score compares your performance with that of people who have normal vision, using an eye chart. Each eye's score is expressed as two numbers, such as 6/6 (20/20) or 6/30 (20/100). The first number is the distance you stand from the chart, usually 6 m (20 ft) 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.

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

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

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 6/6 or 20/20) is found. The result of a refraction test determines your prescription eyeglass or contact lens strength.

A refraction test takes 10 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 centre 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 centre).
• 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.

Colour vision test

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.

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 medical history.

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Author:	Alison Allen	Last Updated: August 16, 2007
Medical Review:	Patrice Burgess, MD - Family Medicine Ian MacDonald, MDCM, FRCSC - Ophthalmology Andrew Swan, MD, CCFP, FCFP - Family Medicine
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