Femtosecond laser-based technique offers opportunities for customised manufacturing and post-implantation modification. Cheryl Guttman Krader reports from ASCRS 2021 in Las Vegas, USA.
Femtosecond laser-induced refractive index shaping (RIS) represents the future for advances in IOL technology and could be the solution for providing perfect refractive outcomes for patients undergoing cataract surgery, Susan MacDonald MD said.
“Refractive index shaping, created with the femtosecond laser, could offer the opportunity to create more sophisticated and customised optical designs that are not possible with currently available manufacturing techniques, which depend on frozen lathing or moulding processes,” Dr MacDonald said.
“In addition, RIS allows for micro-adjustments to implanted IOLs to correct residual spherical or cylindrical errors or add or remove multifocality. These postoperative modifications would reduce the burdens of managing the 20/unhappy patients.”
The RIS technique uses femtosecond laser energy within the IOL optic to create highly localised changes to the lens material’s hydrophilicity. Exposure to the laser pulses results in a photochemical reaction in which esters within the hydrophobic lens material convert into acid and alcohol groups that attract water, increasing in the lens polymer hydrophilicity.
Evidence of RIS technique efficacy is available from preclinical research that also demonstrates the procedure is highly reproducible and does not adversely affect the IOL quality. Citing experiments conducted at the John A Moran Eye Center, University of Utah, Dr MacDonald reported measurements that showed less than 98% of the lens optical transmission was preserved following the femtosecond laser treatment. Measured IOL light transmittance was 97.77% before the RIS procedure, reducing to 96.48% following the laser treatment.
The same researchers also showed modulation transfer function did not significantly change from the RIS procedure. In addition, they reported on the accuracy and repeatability of the technique for creating refractive change.
“The refractive changes are repeatable within 0.1D,” Dr MacDonald said.
This dioptric power precision contrasts with the tolerance limits for manufactured IOLs.
“We know there are many variables affecting our ability to reach our refractive target in patients undergoing cataract surgery, and we are unable to control all of them,” Dr MacDonald said.
“Variation in the power of the manufactured lens is one very important factor. For a 20D IOL, there can be a 0.2D difference between the labelled power and the actual power of the lens. This technology will change the accuracy of lenses produced.”
A lot is going on in this area of research. One approach, laser-induced refractive change index change, LIRIC (Clerio), aims to correct refractive changes in the cornea. The company believes the same approach could also work on IOLs or contact lenses. Another company, PerfectVision, is reportedly working on an approach that uses the laser to adjust an IOL after surgery.
Susan MacDonald MD is Associate Clinical Professor of Ophthalmology, Tufts School of Medicine, Boston, Massachusetts, USA. susanmacdonaldeyecorps@gmail.com
