Adjusting IOL Power in the Eye

Femtosecond laser technology moves toward human trials. Howard Larkin reports from ASCRS in Las Vegas, USA

Afemtosecond laser treatment capable of altering the power and other optical characteristics of commercial intraocular lenses after implantation is on the brink of human trials, reports Liliana Werner MD, PhD.

The investigational treatment uses laser refractive index shaping to alter the IOL refraction in the eye. The femtosecond laser uses green light at 520 nm and operates at energy levels below the threshold for ablation or cuts. It induces a chemical reaction in the targeted area of the IOL optic material that locally increases hydrophilicity, which decreases the refractive index. An inscribed phase wrapping pattern creates a thin lens of different refractive power within the IOL, Dr Werner explained. This process can produce changes such as increasing or decreasing sphere power and adding, subtracting, or cancelling cylinder, asphericity, or multifocality.

SAFE AND EFFECTIVE Extensive safety studies show the laser treatment does not create any toxic substances or leaching from the lens, does not promote glistenings or other lens defects, and maintains stable refractive changes over time that are unaffected by YAG capsulotomy. The process does decrease light transmission slightly, from 83.2±1.4% before adjustment to 81.8±1.8% afterward (as observed in an in vitro study with a specific commercially available IOL), and increases backlight scatter, but at levels not thought to be clinically significant, Dr Werner said. Modulation transfer function curves are virtually unaffected by the adjustment of -2.0D on the same IOL.

In a short-term in vivo rabbit study, commercially available monofocal hydrophobic IOLs were implanted in both eyes of six New Zealand rabbits and adjusted using the laser to target adding 3.6 dioptres sphere, a treatment that took 23 seconds. The only side effect was gas bubbles behind the lens that disappeared within a few hours. There were no inflammatory reactions or damage to the IOLs observed. Four weeks after implantation, clinical outcomes were similar between treated and untreated controls implanted with the same IOLs. Refractive outcomes for treated lenses were close to target with a mean of +3.7±0.03D, Dr Werner reported. A sixmonth study involving seven rabbits also found no significant differences between treated and untreated animals.

The laser also can be used to customise the lens before implantation, allowing more changes than can be made in vivo, Dr Werner said.

“The advantage is the laser can turn a monofocal IOL into a custom multifocal IOL in an affordable manner.”

It eliminates the need for highly trained technicians and large capital and inventory investments to manufacture premium lenses, she added.

Trials were set to begin last year in Panama were postponed due to COVID-19, but should resume soon.

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