Objective: To determine the correlation between measured and computed magnification caused by a change in the plane of correction from the spectacle plane to the corneal plane in myopic refractive surgery.
Methods: Fourteen patients who underwent radial keratotomy and five normal volunteers served as subjects. Anticipated relative magnification was computed and measured by means of a direct-comparison eikonometer. Measured values were correlated to the anticipated magnification effects determined by computation.
Results: Measured and computed magnifications were highly correlated (r = .891).
Conclusions: Magnification induced by refractive surgery can increase visual acuity in excess of 1 line for myopic corrections or similarly decrease visual acuity for hyperopic corrections. Magnification effects can be modeled accurately by means of computational methods. When clinical studies are designed to evaluate refractive surgery, ignoring the effects of magnification is similar to saying that visual acuity can be measured with and without the aid of a magnifier and the results directly compared.