• Sample size calculations are shown for some common ophthalmologic study designs in which two treatments are to be compared. Included are the following three designs: 1, only one eye per subject; 2, both eyes, with each eye assigned to a different treatment; and 3, both eyes undergoing a common treatment. Continuous and binary outcomes are considered. The correlation between eyes is accounted for in the computations using a simple correction factor. For design 3, the formulas allow for a mixture of single-eye and double-eye eligible subjects. A computer program that performs the calculations is available.
Gauderman WJ, Barlow WE. Sample Size Calculations for Ophthalmologic Studies. Arch Ophthalmol. 1992;110(5):690-692. doi:10.1001/archopht.1992.01080170112036