Colour Vision Impairment in Young Alcohol Consumers

Abstract

Alcohol consumption among young adults is widely accepted in modern society and may be the starting point for abusive use of alcohol at later stages of life. Chronic alcohol exposure can lead to visual function impairment. In the present study, we investigated the spatial luminance contrast sensitivity, colour arrangement ability, and colour discrimination thresholds on young adults that weekly consume alcoholic beverages without clinical concerns. Twenty-four young adults were evaluated by an ophthalmologist and performed three psychophysical tests to evaluate their vision functions. We estimated the spatial luminance contrast sensitivity function at 11 spatial frequencies ranging from 0.1 to 30 cycles/degree. No difference in contrast sensitivity was observed comparing alcohol consumers and control subjects. For the evaluation of colour vision, we used the Farnsworth-Munsell 100 hue test (FM 100 test) to test subject's ability to perform a colour arrangement task and the Mollon-Reffin test (MR test) to measure subject's colour discrimination thresholds. Alcohol consumers made more mistakes than controls in the FM100 test, and their mistakes were diffusely distributed in the FM colour space without any colour axis preference. Alcohol consumers also performed worse than controls in the MR test and had higher colour discrimination thresholds compared to controls around three different reference points of a perceptually homogeneous colour space, the CIE 1976 chromaticity diagram. There was no colour axis preference in the threshold elevation observed among alcoholic subjects. Young adult weekly alcohol consumers showed subclinical colour vision losses with preservation of spatial luminance contrast sensitivity. Adolescence and young adult age are periods of important neurological development and alcohol exposure during this period of life might be responsible for deficits in visual functions, especially colour vision that is very sensitive to neurotoxicants.

Fig 1. Spatial luminance contrast sensitivity of young alcohol consumers compared with tolerance limits for the control group.

Young alcohol consumers had contrast sensitivity in the normal range. Data from alcohol consumers (circles) are located in the tolerance interval (dashed red lines) with the exception of a single data point from one subject that had contrast sensitivity lower than the lower tolerance limit a 2 cpd. Smokers and non-smokers among the alcohol consumers are identified with red and empty circles, respectively. There were no obvious differences between the two groups that could indicate an aggravation of the psychophysical performance of alcohol consumers by the smoking habit.

Fig 2. Colour arrangement performance of young alcohol consumers in the FM 100 test compared with performance of young non-alcohol consumers.

Examples of individual performance. A) Results for three young non-alcohol consumers. Subjects from this group always had small total scores. Top to bottom: subjects C01020222 (right eye, 21 years old), C02000111 (right eye, 20 years old), and C03010429 (right eye, 18 years old) had total scores of 53 ± 19, 13 ± 7, and 36 ± 9, respectively. Β) Results for three young alcohol consumers. Some subjects from this group performed similarly to controls in this test while others made more mistakes than predicted by the upper tolerance limits for controls. Top to bottom: subjects S15100325 (Right Eye, 23 years old), S08100807 (Right Eye, 24 years old), and S01090617 (Right Eye, 20 years old) had total scores of 28 ± 3, 152 ± 10, and 326 ± 30, respectively. See text for additional details.

Fig 3. Colour arrangement performance of young alcohol consumers in the FM 100 test compared with performance of young non-alcohol consumers.

Results for the two groups. A) Total errors for young alcohol consumers compared with the upper tolerance limit for young non-alcohol consumers. Half of alcohol consumers made more mistakes than the upper tolerance limit estimated for the control group, 100.7. Smokers and non-smokers among the alcohol consumers are identified with red and empty circles, respectively. There were no obvious differences between the two groups that could indicate an aggravation of subjects’ performance in the hue arrangement test by the smoking habit. Β) Comparison between means and standard deviations for controls (empty column) and alcohol consumers (filled column) (log values). Alcohol consumers had higher total errors than controls; their results were also more variable. (*) Statistical significance (P < 0.01, Student t test).

Fig 4. Colour discrimination ellipses from young alcohol consumers obtained with the MR test compared with young non-alcohol consumers.

Examples of individual performance. Five regions of the colour space were studied. Data points from colour discrimination thresholds were plotted in the CIE 1976 colour space and then fitted to obtain the corresponding MacAdam colour discrimination ellipses. A) Colour discrimination ellipses obtained from a control subject (C04 020620 Right Eye, 20 years old). Β) Colour discrimination ellipses obtained from a young alcohol consumer (S02100805, right eye, 22 years old). Some alcohol consumers had colour discrimination ellipses larger than controls, but data for the majority of them fell in the normal range. There was no preference in the colour space for threshold increase in young consumers.

Fig 5. Colour discrimination ellipses from young alcohol consumers obtained with the MR test compared with young non-alcohol consumers.

Results for the two groups. A) Diameter of colour discrimination ellipses obtained from young alcohol consumers (circles) compared with upper tolerance limits for controls. Ellipse diameter was taken as the diameter of a circle with equivalent area. Depending on the ellipse, E1 to E5, between 1 and 5 subjects had ellipses larger than the upper tolerance limits. Smokers and non-smokers among the alcohol consumers are identified with red and empty circles, respectively. There were no obvious differences between the two groups that could indicate an increase in colour discrimination thresholds of alcohol consumers by the smoking habit. Β) Means and standard deviation for ellipse diameters obtained from young alcohol consumers (filled bars) and controls (empty bars). For all ellipses, E1 to E5, the group of alcohol consumers had larger ellipses than the group of non-alcohol consumers, but statistical significance was reached only for E1, E3, and E5 (P < 0.05, ANOVA).