Red-green color vision impairment in Duchenne muscular dystrophy

Abstract

The present study evaluated the color vision of 44 patients with Duchenne muscular dystrophy (DMD) (mean age 14.8 years; SD 4.9) who were submitted to a battery of four different color tests: Cambridge Colour Test (CCT), Neitz Anomaloscope, Ishihara, and American Optical Hardy-Rand-Rittler (AO H-R-R). Patients were divided into two groups according to the region of deletion in the dystrophin gene: upstream of exon 30 (n=12) and downstream of exon 30 (n=32). The control group was composed of 70 age-matched healthy male subjects with no ophthalmological complaints. Of the patients with DMD, 47% (21/44) had a red-green color vision defect in the CCT, confirmed by the Neitz Anomaloscope with statistical agreement (P<.001). The Ishihara and the AO H-R-R had a lower capacity to detect color defects--5% and 7%, respectively, with no statistical similarity between the results of these two tests nor between CCT and Anomaloscope results (P>.05). Of the patients with deletion downstream of exon 30, 66% had a red-green color defect. No color defect was found in the patients with deletion upstream of exon 30. A negative correlation between the color thresholds and age was found for the controls and patients with DMD, suggesting a nonprogressive color defect. The percentage (66%) of patients with a red-green defect was significantly higher than the expected <10% for the normal male population (P<.001). In contrast, patients with DMD with deletion upstream of exon 30 had normal color vision. This color defect might be partially explained by a retina impairment related to dystrophin isoform Dp260.

Figure 1.

Left, Image of the stimulus provided by the CCT, showing the spatial and luminance noise (small patches of different diameters and luminances) and the letter “C” formed by the same patches at a chromaticity that differs from the background. Right, CIE chromaticity diagram (1976 u′v′) used by the CCT. The gray area indicates all colors seen by the human visual system, and the color triangle exhibits the chromaticities that can be displayed by the video monitor at the luminance level used in the tests. The lines P, D, and T correspond to the protan, deutan, and tritan, respectively, confusion lines tested in the Trivector protocol.

Figure 2.

Color discrimination thresholds of the patients with DMD and control subjects (mean±SD) for the protan, deutan, and tritan confusion lines of the Trivector test. Statistical difference was significant for all three confusion lines.

Figure 3.

Patients with DMD stratified according to their color vision deficiencies, with their region of dystrophin gene deletion shown. The range of deletion is indicated numerically in the first column. For each patient, the length of the DMD gene is shown by a horizontal black line that represents the extension and location of deletion in this gene. A, All the patients with color vision impairment. All patients had deletions downstream of exon 30. B, Patients with normal color vision classification. The majority have deletions upstream of exon 30.

Figure 4.

Color discrimination results for the control subjects and patients with DMD, grouped according the region of the gene deletion (mean±SD) for protan, deutan, and tritan confusion lines. Statistical difference was found between the controls and the patients with deletion downstream of exon 30, for all the confusion lines.

Figure 5.

The mean area of the CCT ellipses for controls and for the patients with DMD stratified into two groups: those with deletion downstream or upstream of exon 30. The area of color discrimination ellipses quantify the ability of the subject to discriminate color in all directions around a point in the chromaticity diagram. The smaller the area, the better the discrimination. The downstream group shows statistically significant wider ellipses areas or reduction in color discrimination, compared with the other two groups.