IOL power adjustment
Non-invasive femtosecond laser technique provides accurate refractive adjustment to IOLs without harmful effects
Liliana Werner MD, PhD
In vitro and in vivo studies show that the femtosecond laser can be used to perform multiple intraocular lens (IOL) power adjustments with a high degree of accuracy and can add premium features to the most commonly used lenses, said Professor Liliana Werner MD, PhD, John A Moran Eye Centre, University of Utah, Salt Lake City, Utah.
“IOL power adjustment with a femtosecond laser can be used in hydrophilic or hydrophobic IOLs. It is non-invasive and only requires topical anaesthesia. It can add and remove premium functions. And unlike the light-adjustable lens, it requires no special spectacles before the locking in of the refractive change,” Prof Werner told the 37th Annual Congress of the ESCRS in Paris, France.
The femtosecond laser IOL power adjustment system was developed by Perfect Lens LLC (Irvine, CA, USA). Using green light with a 520nm wavelength, the laser operates at energy levels that are below the threshold for ablation or cuts. It enables the power adjustment of previously implanted commercially available acrylic IOLs. The laser induces a chemical reaction in a targeted area of the IOL optic substance causing a localised increase in hydrophilicity. That, in turn decreases the refractive index in that area which can be used to increase or decrease the IOL’s dioptric power, among other adjustments.
In vitro studies carried out by Dr Werner and her associates have shown that in the laboratory setting the laser technique can modify refraction with a high degree of accuracy. In commercially available hydrophobic IOLs that underwent femtosecond laser power adjustment with a targeted change of 2.0D, the mean change was 2.03D. The studies also showed that the technique can convert a standard hydrophobic monofocal IOL to a multifocal and then back.
The studies also show that the treatment does not affect the clarity of the lens to the point where it became clinically significant. For example, a mean power change of -2.037D was associated with a modulation transfer function (MTF) change of -0.064 cycles/mm and reduced light transmittance, as measured by spectrophotometry, by only 1.4%. Backlight scattering, as measured with a Scheimpflug camera, increased within the IOL optic in the zone corresponding to the laser treatment at levels that are not expected to be clinically significant (Nguyen J, Werner L, Ludlow J, et al J Cataract Refract Surg. 2018;44(2):226-230).
Commercially available hydrophobic acrylic IOL after in vivo
(rabbit model) power adjustment by femtosecond laser
Results from in vivo studies with the rabbit eye model showed similar accuracy of refractive change and also support the biocompatibility of the technique. In a series of six rabbits implanted with a commercially available single-piece hydrophobic acrylic IOL, the femtosecond laser adjustment with a target of +3.6D resulted in a mean change of +3.7D. In addition, slit lamp examination showed no inflammatory reaction and there were no glistenings or damage to the IOL (Werner L, Ludlow J, Nguyen J, et al J Cataract Refract Surg. 2017;43(8):1100-1106).
Furthermore, no postoperative inflammation or toxicity was observed in the treated eyes, and postoperative outcomes and histopathological examination performed two weeks postoperatively showed results were similar to those in untreated eyes. The change in power obtained was consistent and within ±0.1D of the target.
A second in vivo eye study supported those findings. It involved rabbits implanted bilaterally with a commercially available hydrophobic IOL and femtosecond laser power adjustment was done in one eye of each rabbit between two and three weeks afterwards. At six months’ follow-up, slit-lamp examination showed there was again no inflammatory reaction or glistenings or damage to the IOL and again implant cytology and histopathology showed no significant differences between the laser-treated and nontreated eyes.
In addition, there was no difference between the two groups in terms of the late complications typical in the rabbit model, such as significant posterior capsule opacification, synechiae, partial pupillary optic capture and cell deposits.
Dr Werner noted that the first human trials with femtosecond laser adjustment are due to begin shortly in Panama. She added that it is conceivable that a femtosecond laser system could be designed with which a surgeon could perform not only IOL power adjustment, but also femtosecond laser-assisted cataract surgeries and corneal refractive procedures such as LASIK and SMILE.
Liliana Werner: firstname.lastname@example.org