Test-retest Repeatability of the Ohio Contrast Cards

Abstract

Significance: The Ohio Contrast Cards are a repeatable test of contrast sensitivity, and they reveal higher contrast sensitivity for low-vision patients than is shown by the Pelli-Robson chart.

Purpose: This study aimed to compare the contrast sensitivity results and test/retest ±limits of agreement for the Ohio Contrast Cards and the Pelli-Robson letter contrast sensitivity chart on two challenging groups of participants, and to compare the Ohio Contrast Card results with grating acuity and the Pelli-Robson results with letter acuity.

Methods: The Ohio Contrast Card and Pelli-Robson tests were each performed twice by two different examiners within one visit on 40 elder patients in Primary Vision Care (>65 years old) and 23 to 27 low-vision school-aged students. Grating acuity was measured using the Teller Acuity Cards (all participants), and letter acuity was measured using ClearChart (elders) or the Bailey-Lovie chart (students).

Results: The ±95% limits of agreement were similar for the Ohio Contrast Cards and the Pelli-Robson chart. The elders' limits of agreement were ±0.27 (Ohio Contrast Cards) and ±0.28 (Pelli-Robson); the students' limits of agreement were ±0.42 (Ohio Contrast Cards) and ±0.51 (Pelli-Robson). However, Ohio Contrast Card results were 0.41 log10 Michelson units more sensitive than the Pelli-Robson chart (over one line on the Pelli-Robson chart) for the elders and 0.90 log10 Michelson units (three lines on the Pelli-Robson chart) more sensitive for the elders (0.11 and 0.6 log10 Weber units, respectively). The Pelli-Robson results were correlated with letter acuities and Ohio Contrast Card results for both groups, and the Ohio Contrast Card results were correlated with Teller Acuity Card acuities for the elders.

Conclusions: The Ohio Contrast Cards and Pelli-Robson chart are similarly repeatable. Both contrast sensitivity tests can provide additional clinical information that is not available through visual acuity testing, and Ohio Contrast Card may provide additional information not available from the Pelli-Robson chart.

Figure 1.

Signed differences between paired, repeated measurements of contrast sensitivity, as a function of their means. Measurements made using Pelli-Robson charts (A, C) or Ohio Contrast Cards (B, D). A, B, 40 elders; C, 23 low-vision students; D, 27 low-vision students. Dotted lines, mean difference between the first and second tests. Numbers, limits of agreement. Solid lines, means +/− 95% Limits of Agreement. The absyssa numbers for the Ohio Contrast Cards are in Michelson units, with the corresponding Weber units below in parentheses. Notice the different y-axis ranges for the elders and the students. Data points with the same coordinates have been displaced by ±0.05 or less for clarity.

Figure 2.

Association between results measured using grating cards and letter tests. Dashed lines of unit slope: equality. White triangles, 40 elders; black circles, 23 students. Elders’ data with the same coordinates have been displaced laterally by ±0.05 or less for clarity. A, Ohio Contrast Card contrast sensitivity as a function of Pelli-Robson contrast sensitivity. Left-hand axis, contrast sensitivity in Michelson units, applied to the data and the “M” equality line. Right-hand axis, contrast sensitivity in Weber units, applied to the data and the “W” equality line. Long regression line fit to student data: r=.59, P=.002. Short line fit to elder data, excluding the influential outlier at x=0.775: r=0.47, P=.002. Fine dotted horizontal line, maximum sensitivity available from the Ohio Contrast Cards. B, Teller Acuity Card acuity as a function of letter acuity. Long bold line fitted to the student data, r=0.66, P=.001. Short regression line fitted to the elder data, R=0.49, P=.002.

Figure 3.

Comparison between contrast sensitivity and visual acuity, with correlation coefficients and regression lines. A, B, 40 elders; C, 24 low-vision students; D, 27 low-vision students. A, C, letter charts; B, D, grating cards. In A, one influential outlier was excluded from the regression analysis. In figure section C, the arrow indicates the nominal log₁₀cy/deg of the Pelli-Robson letters. Elders’ data with the same coordinates have been displaced laterally by ±0.05 log₁₀units or less for clarity.