Table 2. Agreement and Differences in BCVA Letter Score: Number or Landolt C Charts vs Alphabet Charts.
| ETDRS Chart Type | Concordance Correlation Coefficient (95% CI)a | Difference in Letter Scores (95% CI)b | ||||||
|---|---|---|---|---|---|---|---|---|
| Group A (20/20-20/25) | Group B (20/20-20/40) | Group C (20/50-20/100) | Group D (20/125-20/200) | Group A (20/20-20/25) | Group B (20/20-20/40) | Group C (20/50-20/100) | Group D (20/125-20/200) | |
| Number vs alphabet | 0.89 (0.82 to 0.93) | 0.97 (0.94 to 0.98) | 0.92 (0.86 to 0.96) | 0.96 (0.87 to 0.99) | 1.16 (−2.98 to 5.29) | 0.70 (−3.96 to 5.36) | 0.94 (−6.17 to 8.05) | 0.21 (−4.98 to 5.41) |
| Landolt C vs alphabet | 0.72 (0.52 to 0.83) | 0.83 (0.68 to 0.91) | 0.79 (0.61 to 0.89) | 0.89 (0.66 to 0.97) | −4.80 (−13.5 to 3.91) | −7.56 (−20.12 to 5.00) | −8.04 (−21.33 to 5.26) | −6.36 (−14.07 to 1.35) |
| P valuec | .003 | <.001 | .01 | .11 | <.001 | <.001 | <.001 | .001 |
Abbreviations: BCVA, best-corrected visual acuity; ETDRS, Early Treatment Diabetic Retinopathy Study.
a
Concordance correlation coefficients were calculated from intraclass correlation (interpretation: <0.40, poor; 0.40-0.59, fair; 0.60-0.74, good; and 0.75-1.00, excellent).
b
Negative sign indicated that the ETDRS letter scores were less than those measured with the alphabet chart.
c
P values for the differences in agreement (intraclass correlation coefficients) were calculated using the F test, and the P values for the differences in letter scores across charts were calculated using the Wilcoxon signed rank test.