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Table 1 Cup to disc ratio means and comparisons among the 3 brightness settings

From: The effect of photographic light brightness on cup to disc ratio grading

Mean c/d ± SD Dark (n = 50) Medium (n = 50) Bright (n = 50)
0.47 ± 0.11 0.48 ± 0.11 0.53 ± 0.12
  Dark vs. Medium Dark vs. Bright Medium vs. Bright
P value* 0.3030 < 0.0001 < 0.0001
  1. The mean c/d gradings for each of the 3 brightness groups, dark, medium, and bright, were compared to each of the others using paired t tests*; c/d (cup to disc ratio), SD (standard deviation)