Differences in FM100-Hue test performance related to iris colour may be due to pupil size as well as presumed amounts of macular pigmentation

Abstract

Background: It has been reported that the differences in macular pigment between Asian and Caucasian eyes might give rise to different performance on the Farnsworth-Munsell 100 Hue test. However, the study did not appear to account adequately for the observation that differences were apparent only in older age groups. It was also acknowledged that other factors, like pupil size and crystalline lens colouration, could influence the result.

Method: We investigated the performance of the Farnsworth-Munsell 100 Hue test, under standard conditions, by three groups with presumed different macular pigmentation and narrow age range. We also measured pupil size.

Results: The group with blue irides (presumed low macular pigmentation) performed significantly better on the colour vision task than the Asian group and the brown-eyed subjects as a whole (presumed higher macular pigmentation). In addition, the difference in pupil size between the blue-eyed group and brown-eyed groups bordered on significance. The difference in pupil size and consequential reduction in retinal illuminance account for a significant proportion of the difference in colour vision performance. In addition, a difference in both pupil size and Farnsworth-Munsell 100 Hue test performance was also observed between males and females that reinforced the importance of pupil size, and not just macular pigment, as a factor in colour vision performance difference between Asian and non-Asian eyes.

Conclusion: It is concluded that pupil size, not just macular pigment, may have a significant influence on colour vision performance in a young, healthy population.