Laser technology has potential to modify IOL refractive index without change to lens shape
Hydrophilicity refractive index shaping has potential to alter the refractive qualities of the cornea without changing its shape.
Reviewed by George O. Waring IV, MD, FACS
Developing femtosecond laser technology can change the refractive qualities of an IOL after it has been implanted.
The same technology, hydrophilicity refractive index shaping (RIS), has the potential to alter the refractive qualities of the cornea without changing its physical shape.
“This is a new paradigm and is potentially huge in refractive surgery,” said George O. Waring IV, MD, FACS, founder of Waring Vision Institute, Mount Pleasant, SC, and adjunct assistant professor of bioengineering, Clemson University. “It could change the ways we approach refractive surgery, either at the IOL plane or at the corneal plane.”
Dr. Waring described the current state of refractive index shaping as applied to acrylic IOLs. He is a consultant to Perfect Lens LLC, one of several companies developing RIS platforms and applications.
“What is being done is utilizing a femtosecond laser to selectively change the refractive index of the target material, which changes the optical properties of how a refractive material performs,” Dr. Waring said.
“You can essentially create a shape with a material plane, create a three-dimensional structure within an existing physical space without changing or disrupting the surface of the material or the tissue where the effect is aimed,” he said. “You can create a lens within a lens without disrupting the surface of the material, in this case an IOL.”
The femtosecond laser very precisely affects the hydrophilicity of the target material to alter its refractive characteristics in a limited area, Dr. Waring continued. The technology also exploits Fresnel optics to produce an effect called phase wrapping.
“Phase wrapping allows you to effect a large optical change efficiently in a small physical space,” he said. “This allows for larger treatments within an IOL. This could potentially offer numerous benefits in a clinical setting, in the laser suite, because the entire process is minimally invasive.”
Benchtop testing promises a wide variety of clinical applications. The technology allows the ophthalmologist to take control of most optical properties and qualities that affect both additive and subtractive measures, including spherical aberration, asphericity, toricity and multifocality.
The femtosecond laser that alters the optical qualities of the IOL is a proprietary application using a dedicated device, Dr. Waring said, but the laser form factor and liquid optic interface are intuitive and familiar to anyone who is used to docking or utilizing the femtosecond laser instruments now in clinical use.
The entire process is image guided and has been tested across multiple brands of acrylic IOPs with a high degree of precision across brands.
While the technology still needs further testing and clinical trials, benchtop test results are dramatic. The power of an IOL can be reduced, or increased, up to six diopters. And once changed, the power can be changed and adjusted at least multiple times without significantly affecting the modulation transfer function of the lens.
Spherical aberration can be adjusted to customize an off the shelf IOL to the patient’s own optics. Starting with a non-toric monofocal lens, RIS makes it possible to create a spherical and/or astigmatic pattern a treatment unique to each patient.
For patients implanted with a monofocal lens who later wish they had opted for a multifocal implant, RIS may offer a solution. Benchtop tests show a monofocal lens can be converted into a multifocal lens, and vice versa. The most important optical change when converting from monofocal to multifocal functionality is a reduction in modulation transfer function because light is now being redistributed across multiple foci.
“It appears that we may also be able to reverse multifocality for people who have struggled with this technology,” Dr. Waring said. “And when going from multi- to monofocal, we see increased modulation transfer function because we are reassigning light to the same focal point.”
Changes in modulation transfer function also make it possible to adjust the amount of light allocated to different focal points within a multifocal lens. That opens the door to customized light levels for near, intermediate, and far vision, depending on patient preference and visual need, he noted. It could also be possible to change the light allocation to the different focal points sequentially to allow for neuroadaptation over several weeks or months to improve the patient’s perception of visual quality.
Look to the future
“The most common opportunities for the refractive types of enhancements that are currently done, small enhancements with laser vision correction, piggyback IOLs or IOL exchange, these can all be done in minimally invasive fashion using laser light in the clinic with this technology,” Dr. Waring said.
“Sequential treatments appear to be possible, so power and other qualities could be changed over one’s lifetime or until the patient is happy with the result,” he added. “And because acrylics can be optimized for this technology, it is entirely conceivable that we could be customizing lenses even before they go into patients’ eyes and then tweaking each lens as needed after implantation.”
George O. Waring, IV, MD, FACS
This article was adapted from Dr. Waring’s presentation during Refractive Surgery Day at the 2018 meeting of the American Academy of Ophthalmology. He did not indicate financial interest in the subject matter.