Table 4

Sample size calculations

Total patients required, using standard deviation of
Type of study20125013100131420015300*
Uniocular surgery or treatment using fellow eye as control (one group)†62490351787
Two groups of uniocular surgery or treatment‡18 (9 per group)90 (45 per group)352 (176 per group)1398 (699 per group)3142 (1571 per group)
  • α=0.05, power=0.8 for all calculations.

  • Difference to detect is 30 µm CRT, either to the fellow eye or to other treatment/surgery group. Assuming none lost to follow-up. Examples of literatures using the mentioned SDs are also given.

  • *Based on literatures that severe cases of diabetic macular oedema might exhibit CRT up to 600 µm, leading to a total SD of approximately 300 µm.16

  • †At -test for comparing difference between two dependent means (matched pairs), for example, study assessing impact of phacoemulsification on the retina in comparison with the fellow eye.

  • ‡At test for comparing difference between two independent means (two groups), for example, study assessing two phacoemulsification types.