Phakic IOLs better than LASIK for high myopia

Phakic IOLs offer slightly better results than LASIK for high myopia Dr Pablo Artal, of the Optical Laboratory in the University of Murcia in Spain, told delegates.

"For low degrees of refractive error, LASIK provides good results, but with high degrees of ammetropia the procedure is more difficult and the outcome less sure, " he said. "I wanted to test purely the optical performance of the two procedures to see which performed better. "

Dr Artal sought to compare the optical performance between LASIK and phakic IOL implantation using virtual surgery on a -8D patient, which he then compared to real results on operated eyes. For the virtual operation Dr Artal used customized ray-tracing modelling, using real patient data, to predict took data from real eyes.

The test used topography to trace the corneal surface, and IOL master (Carl Zeiss Meditec) to measure eye geometry, which was compared to wavefront measurements. The lens position was assessed using the Purkinje meter while the Zemax ray-tracing engine completed the model.

The experiment then adjusted the data to account for a standard LASIK treatment for high-myopia and a standard phakic IOL. "Using optimized LASIK or an optimized phakic IOL may obtain a better result for each procedure, " he said.

Postop analysis of both virtual surgeries showed a slight, but noticeable, difference between the two procedures. The phakic IOL showed a better result in both Radial MTF and retinal image quality. These results were from a theoretically 'standard' case.

Dr Artal then induced some theoretical spherical aberration as a function of the preop refractive state. The results showed that LASIK increased spherical aberration postop as the degree of myopia increased, from -2D to -8D.

Meanwhile, SA induced by the phakic IOL remained static or decreased slightly as the degree of correction increased from -4 to -10D. The predicted optical differences in spherical aberration were approximately 0.1 mm, but the observed differences following real operation among eight high myopes revealed a corneal SA of approximately 0.4 mm.

Finally, Dr Artal looked at direct measurements of retinal image quality in post-LASIK and post-IOL patients. These measurements showed that optical performance of phakic IOLs is slightly superior to LASIK, though less than predicted from corneal data.

Dr Artal emphasized that this experiment examined optical quality only, and there were many other variables not accounted for. But he said he believed it was a validation of virtual surgery and it was suggestive that phakic IOLs cope better with extreme myopia than LASIK does.

"Virtual surgery is a very useful procedure for a wide variety of cases, " Dr Artal said. "In this case we looked at a very simple case, and it shows interesting results. But it is possible to make far more sophisticated models, to account for many different factors and to test several possible solutions to extreme cases of ammetropia, for example. "