Experimental verification of computational methods to calculate magnification in refractive surgery
R. A. Applegate and U. Chundru
Department of Ophthalmology, University of Texas Health Science Center at San Antonio, USA.
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.
