In comparisons of retinal image size within the same eye before and after refractive surgery, a change in the plane of correction from the spectacle to the cornea induces a change in retinal magnification. Comparing retinal image size between eyes of different individuals, a change in the plane of correction as well as the type of ametropia (axial or refractive) interacts to change the retinal magnification. Consequently, comparing acuity before and after refractive surgery without considering the effects of retinal magnification can be misleading. Magnification effects can be large, accounting for a visual acuity increase of 1 line or more. Here we model the magnification induced by refractive surgery in various reference eyes and discuss implications in the context of current clinical trials.
Applegate RA, Howland HC. Magnification and Visual Acuity in Refractive Surgery. Arch Ophthalmol. 1993;111(10):1335-1342. doi:10.1001/archopht.1993.01090100043025