Material
- Ishihara colour test chart [Figures 27, 28].
Figure 27
Figure 28
This consists of a series of charts on which circular shapes are depicted, containing a pattern of dots printed in different shades of red, green, and grey.
Procedure
Allow the patient to hold the book containing the images in front of them and ask which figure or number is seen inside the circle.
This series of charts is built up in a way that a patient with abnormalities of colour vision will or will not recognise numbers and shapes. From the combination of recognised/unrecognised numbers and figures, the nature of the colour vision defect can be deducted.