Colour discrimination under C and high-pressure Na illumination in normals and patients affected by various diseases.

Under illumination produced by a high-pressure sodium lamp, colour discrimination, compared to C illumination, is found to be impaired. In particular, young diabetic patients, without signs of retinal involvement, show the expected decrease in total score as age proceeds from 10 to 25 years under C illumination. This is no longer the case under Na illumination.