Multifocal corneal topographic changes with excimer laser photorefractive keratectomy
H. Moreira, J. J. Garbus, A. Fasano, M. Lee, T. N. Clapham and P. J. McDonnell
Doheny Eye Institute, Los Angeles, CA 90033.
Excimer laser photorefractive keratectomy can flatten the central cornea,
thereby eliminating myopic refractive errors; in older patients, however,
presbyopia limits satisfaction. Computer-assisted topographic analysis of
corneas after refractive surgery indicates that a minority of patients
achieve a multifocal lens effect, such that they maintain reasonable acuity
over a range of defocus. We have purposefully attempted to create a
multifocal refractive effect and have analyzed the subsequent topographies
quantitatively to determine if multifocality was achieved. In corneas not
operated on and plastic hemispheres, a fairly small range of corneal powers
is observed; the range of powers is increased after a monofocal ablation.
After multifocal ablations, a greater spread of surface powers is observed,
often with a bimodal distribution, indicative of an apparent multifocal
effect. These observations suggest that in some patients undergoing
photorefractive keratectomy for myopia, it may be possible to reduce
symptoms of presbyopia, although a decrease in image contrast or monocular
diplopia may complicate this approach.
