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P. Lopez, R.C. Caruso, D. Valle, M. Kaiser–Kupfer; Color discrimination in gyrate atrophy of the choroid and retina . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5157.
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Purpose: Gyrate atrophy (GA) of the choroid and retina (OMIM # 258870) is an autosomal recessive chorioretinal degenerative disease caused by mutations in the OAT gene. Its biochemical hallmark is hyperornithinemia, due to abnormal ornithine–delta–amino–transferase (OAT) function. The aim of this study was to assess the color discrimination of patients with GA, as an estimator of their foveal function involvement. Methods: 34 patients with GA, most of whom had known OAT gene mutations, were included in this study. 29 subjects with normal visual function were used as a control group. Color discrimination was assessed using the Farnsworth–Munsell 100 Hue test. In addition to the traditional error score, the method devised by Vingrys and King–Smith (IOVS: 1988, 29: 50–63) was used to analyze results. This technique yields three outcomes: the confusion angle, which identifies the type of color defect, the C–index, which quantifies its severity, and the S–index, which quantifies its polarity. All confusion angles were expressed as positive values. The Mann–Whitney test was used for statistical comparisons. Results: Using the age–adjusted criterion proposed by Verriest (AJO: 1982, 93: 635–642), 15 of the 34 patients had abnormal color discrimination. Of these, 3 showed a tritan axis, but no specific axis was seen in the remaining 12. Error score was significantly larger in the GA group than in the control group (square root of error score: 12.83 ± 6.97 vs. 5.87 ± 2.97) (mean ± sd) (p < 0.001). Similarly, the C–index was considerably larger in GA patients. (2.35 ± 1.40 vs. 1.28 ± 0.25) (p < 0.001). The confusion angle was larger in the GA group (77.61 ± 19.00 vs. 62.19 ± 9.29) (p < 0.001). The S–index was very similar in both groups (1.32 ± 0.16 vs. 1.32 ± 0.10) (p = 0.86). This was due to the fact that most patients' errors were not restricted to a specific axis. Conclusion: Color discrimination was abnormal in approximately half of the GA patients tested. Severe discrimination defects were seen in all patients in whom chorioretinal atrophy encroached upon the fovea. However, they could also be seen in patients in whom atrophy spared the macula. This suggests that cone function abnormalities in GA may precede foveal atrophy.
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