Colour Vision

Colour vision assessment

Colour vision can be assessed using Ishihara plates, each of which contains a coloured circle of dots. Within the pattern of each circle are dots which form a number or shape that is clearly visible to those with normal colour vision and difficult or impossible to see for those with a red-green colour vision defect.

How to use Ishihara plates

If the patient normally wears glasses for reading, ensure these are worn for the assessment.

1. Ask the patient to cover one of their eyes.

2. Then ask the patient to read the numbers on the Ishihara plates. The first page is usually the ‘test plate’ which does not test colour vision and instead assesses contrast sensitivity. If the patient is unable to read the test plate, you should document this.

3. If the patient is able to read the test plate, you should move through all of the Ishihara plates, asking the patient to identify the number on each. Once the test is complete, you should document the number of plates the patient identified correctly, including the test plate (e.g. 13/13).

4. Repeat the assessment on the other eye.

Normal results

If a client's colour vision is normal, they will be able to distinguish all colours.

What Abnormal Results Mean

This test can determine the following congenital (present from birth) color vision problems:

Achromatopsia -- complete colour blindness, seeing only shades of gray
Deuteranopia -- difficulty telling the difference between red/purple and green/purple
Protanopia -- difficulty telling the difference between blue/green and red/green
Tritanopia -- difficulty telling the difference between yellow/green and blue/green

Problems in the optic nerve can show up as a loss of color intensity, although the colour card test may be normal.

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