Customized IOLs: stability matters

When it comes to correcting spherical aberration (SA) of the whole eye, customized IOLs could be a possible approach for the future. However, if high stability of corneal asphericity during cataract surgery is required, it may be necessary to make some improvements to this approach, according to Jochen Wahl from the University of Mainz, Germany.

Customized intraocular lenses (IOLs) require corneal asphericity to remain stable before, during and after cataract surgery and IOL calculations are based on assumptions which look for the postoperative dense position of the base preoperative data. However, this preoperative data may change during surgery, particularly corneal radii and asphericity. With this is in mind, Dr Wahl and Paul-Rolf Preussner set out to investigate how the corneal surface is influenced by the cataract surgery procedure.

The researchers investigated pre- and postoperative topographies of 50 eyes before and after cataract surgery, and at least two months after the procedure. All eyes were operated on by the same surgeon and all eyes had 3 mm temporal clear-corneal incisions. Best-fitting numerical eccentricity of the optical zone was calculated using the 4 parameter corneal model. “We call this the simple model, because we only need four parameters to describe the cornea: the two vertex radii, the angle of the axis and the asphericity,” Wahl explained.

RMS-errors of spatially resolved refraction and wavefront errors were evaluated in addition by ray-tracing of the whole pseudophakic eye, and implications with respect to best-fitting IOL asphericities were investigated.

The researchers found that the asphericity pre- and postoperatively is highly correlated with the numerical eccentricity, being slightly smaller postoperatively than preoperatively. “The difference is, however, too negligible to meet the requirements of customized optics, and as a result some improvements seem to be necessary for customized IOLs,” said Dr Wahl. “One solution may be sclero-corneal incisions, although this may be a step back. Alternatively, smaller corneal incisions may be a better option for customizing IOLs,” concluded Dr Wahl.