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P. Lopez, R.C. Caruso; The Effect of Stimulus Size on Color Vision Deficiencies in Retinal Disease . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4906.
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Purpose: Dichotomous panel tests are routinely used to diagnose and quantify color vision deficiencies. Two versions which are commercially available are the classical Farnsworth D-15 panel, with 12 mm diameter caps, and a version with 32 mm caps (Precision Vision 16 (PV-16) test). Both color tests can be quantified using the method proposed by Vingrys & King-Smith (IOVS, 1989). The purpose of this study was to compare the results obtained using larger and smaller stimuli in patients with color vision deficiencies of retinal origin. Methods: 32 subjects, all of whom failed the D-15 test, were tested to date (12 patients with color confusions along the blue-yellow axis, 10 patients with confusions along the red-green axes, 4 patients with confusions along the scotopic axis and 6 patients with "anarchic" deficiencies, i.e. without a specific axis). Study parameters were the confusion angle, the confusion (C) index, and the selectivity (S) index, which measure type, degree, and polarity of the color vision defect, respectively. Results were analyzed using parametric and non-parametric statistical tests. Results: Confusion angle: As expected, both tests yielded similar confusion angles, and no statistically significant differences between them were observed (P= 0.79). Therefore, the confusion angles tests showed positive correlation (Spearman rank correlation coefficient rs= 0.58) (P < 0.01). Of the 8 patients in which a difference in defect type between the two tests was seen, 6 of them were classified as defective with the D-15 test and as normal with the PV 16 test. Confusion Index. The C-index was significantly larger with the D-15 (2.98 ± 0.56) (mean ± std. dev.) than with the PV 16 (2.49 ± 0.89) (P < 0.001). The correlation between C-indices yielded by the two tests was good (rs= 0.66) (P < 0.01). Selectivity Index. The S-index was significantly larger with the D-15 (2.87 ± 1.29) than with the PV 16 (2.23 ± 1.19) (P = 0.002). The correlation between S-indices was also good (rs= 0.73) (P < 0.01). Conclusions: In these patients with moderate or severe color vision defects, a larger stimulus size, as expected, yielded a lower error score (smaller C-index). Since some patients who failed the D-15 test passed the PV-16 test, the latter test showed less sensitivity. This decline in C-index was not associated with a desirable increase in the selectivity of the defect (the S-index was also lower). Patients with exclusively macular disease showed a trend towards larger differences in C-index and S-index between the two tests than patients with diffuse retinal disease.
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