Calculating relative retinal image sizes of eyes

I derive simple formulas which accurately give the relative retinal image sizes of corrected eyes. These are useful in calculations involving anisometropia and/or refractive surgery. Using the formulas, I derive simple equations for particular situations and provide two examples. I compare the formulas with the approach adopted by Applegate and Howland (1993) and Applegate and Chundra (1995) to determine relative retinal image sizes before and after refractive surgery.