Acquired Colour Vision Assessment – Is Ishihara Really Enough?

Kylie Green, BAppSci(Orth)
Orthoptic Department, Sydney Hospital & Sydney Eye Hospital, Sydney, Australia

Purpose: A quality improvement project was conducted to determine the most appropriate colour vision test for investigating acquired colour vision loss. The Ishihara Pseudoisochromatic Plate Test (Ishihara) is commonly used in many clinical settings for detecting acquired colour vision defects. However, the Ishihara is a screening test specifically designed to detect congenital red-green colour vision defects. While optic nerve pathology often causes red-green defects, this is not the same as a congenital loss. There is a strong need for in depth colour vision testing to be routinely utilised in clinical settings as colour loss is often the first sign of pathology.

Method: Thirty patients aged 23-76 with suspected optic nerve or macula pathology who were referred to the orthoptic department for colour vision testing, were assessed with the Farnsworth-Munsell 100 Hue (FM 100), Roth 28 Hue (Roth 28) and the Ishihara. The results of these three tests were compared. A control group consisting of 10 patients with no identified pathology were also tested with the FM 100 to ascertain if reliable results can be achieved despite the length of the test.

Results: Of the thirty patients, only one patient had a defect on the Ishihara. The Roth 28 did detect some losses, however, the defects were minimal and not clustered thus the abnormality could not be classified or monitored. The FM100 detected significant changes or abnormalities in colour vision in half of the 30 patients. The 10 control subjects all fell within the high to normal colour discrimination range on the FM 100 hue, with no abnormal axial patterns reported. The significance of these findings is demonstrated by three case studies, which outline the necessity of utilising the FM 100.

Conclusion: The comparison of all three tests shows that the Ishihara is not sensitive enough to detect acquired colour loss and is a poor substitute. While the Roth 28 does detect some colour changes it does not show enough detail to be a useful diagnostic tool. Colour vision testing is a key diagnostic tool and the correct test should be utilised in all clinical settings to aid diagnosis and to monitor progression or regression of optic nerve and macula pathologies.