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The next big thing in surgery?

First-in-human study finds non-invasive refractive index femtosecond laser treatment safe

Howard Larkin

Posted: Friday, November 1, 2019

After a decade in development, a novel femtosecond laser for correcting refractive errors by altering the refractive index of lens materials has passed its first safety trial in humans, Scott MacRae MD told the innovators session at the ASCRS ASOA 2019 Annual Meeting in San Diego, USA.
Using a Laser Induced Refractive Index Correction device (LIRIC, Clerio Vision), 27 monofocal pseudophakic patients received diffractive presbyopia corrections, creating a +2.5D add across a 3.0mm optical zone about 240 microns deep in the corneal stroma. All corneas were clear immediately after treatment and at one day, one week, one month and three months’ follow up.
No inflammation, light scatter, scarring or opacities were observed at any point. Mean corneal thickness change was -2.0±1.8%, and endothelial cell loss was negligible, establishing the safety of the LIRIC device in living humans, Dr MacRae reported.
“LIRIC is a potentially safer, better way to refine the optics of the eye. It is a disruptive technology with the potential to revolutionise refractive surgery, cataract surgery and adjusting contact lenses,” said Dr MacRae, of the University of Rochester, New York, USA.

Multiple applications
Unlike femtosecond and excimer lasers that change refractions by cutting and ablating corneal tissue, LIRIC does so by changing the refractive index of corneal stroma. This creates diffractive Fresnel arrays that can correct sphere, cylinder and higher order aberrations, and add multifocality. Tests in animals and now humans show an increase in density and decrease in water in collagen treated by the laser, which is thought to change the refractive index, Dr MacRae said.
LIRIC does minimal tissue damage, Dr MacRae added. Operating at a pulse energy of about 2.5 nanojoules, the LIRIC laser operates far below the 50-nanojoule threshold of tissue damage, and even farther below the 150-to-1,000 nanojoules of flap-cutting lasers. As a result, corneal cell death is far less than in femto-LASIK and no nerve fibers are cut. The epithelium remains intact, so no antibiotics are required.
In addition to corneal tissue, LIRIC can change the refractive index of hydrogel and acrylic materials. This makes it possible to create multifocal contact lenses and increase the power of monofocal contacts without adding thickness, enabling customisation in refraction and size, and increasing oxygen permeability. LIRIC can also correct residual refractive error in implanted intraocular lenses, and add or subtract multifocality, Dr MacRae said.
Preclinical tests show the optical quality of LIRIC corrections is very high, with negligible effect on visual acuity, contrast sensitivity, modulation transfer function or light scatter. Animal tests suggest corneal corrections are stable for at least two years. More clinical tests of the device are planned.

Scott MacRae: scott_macrae@urmc.rochester.edu