Colour vision tests to assess changes due to acquired colour vision defects have to be of the type D-15, saturated and desaturated, or 100-hue. These tests are difficult to handle if the visual field is limited or when the patient has central scotoma. Also, the size of the caps are so small that the stimulus becomes too little in many cases of central scotoma. The Panel 16 test with its larger stimulus area is useful in assessment of impaired vision.
If inherited colour vision defects are screened, the regular Ishihara and HRR can be used with no difficulty in the examination of deaf patients.