Customised myopic LASIK using automated ray tracing optimisation has the potential to offer improved and more predictable outcomes, a study shows.
Customised myopic LASIK using automated ray tracing optimisation appears to offer improved and predictable results. The procedure is driven by artificial intelligence (AI) and represents a clear step forward in LASIK technology.
The roots of the technology can be traced to topography-guided treatments introduced in Europe in the early 2000s; the treatment approach ultimately led to the introduction of the Athens Protocol, which combines topography-guided and partial transepithelial photo-reactive keratectomy and corneal crosslinking.
“The topography-guided treatments were used to treat sick or problematic eyes, with enlargement of optical zone and treating irregularities such as those seen in keratoconic eyes,” noted Dr A. John Kanellopoulos from the LaserVision Clinical and Research Eye Institute in Athens, Greece, and New York University Medical School, United States.
The advancements in the technology are demonstrated by the surgeon’s ability to treat, for example, a herpetic scar. The topography-guided procedure can return the cornea to a normal state; in contrast, before the availability of the technology, a corneal transplant might be considered in a patient who was contact lens intolerant.
The technology can also be used to treat normal eyes, Dr Kanellopoulos explained. “Use of TMR [topography-modified refraction] in routine myopic eyes not only achieves emmetropia but also pushes the envelope to achieve significant gains in lines of vision postoperatively,” he said.
This technology was initially theoretical and difficult to perform, Dr Kanellopoulos recounted, because of the extensive team diagnostics required and calculations by the surgical team. The advent of ray tracing first validated the effort to push refractive surgery beyond wavefront-optimised treatments and standard clinical refractions to the next level.
Testing the method
Dr Kanellopoulos and Dr Dylan Stevens evaluated both eyes of 25 cases in a consecutive case series that were treated with femtosecond laser-assisted myopic LASIK. The eyes were evaluated for all refractive parameters. Dr Stevens is also from the LaserVision Clinical and Research Eye Institute in Athens, Greece, and New York University Medical School.
These procedures differ from the standard method by using a novel wavelength outcome AI platform, which calculates the ablation profile based on measurements from a single device, the Sitemap (Alcon). This device performs three types of measurements for each patient: axial length measurements with interferometry, Scheimpflug tomography and Hartmann-Shack wavefront analysis. The investigators evaluated the visual acuity, refractive error, keratometry, topography, high-order aberrations and contrast sensitivity during 3 months of follow-up.
The AI of the InnovEyes software calculates the low and higher-order aberrations for each eye in four steps and performs ray tracing in two opposite directions in a model eye using the axial length measurements obtained previously. The corneal topography measurements are then used to calculate the propagation of 2,000 light rays through the anterior corneal surface, corneal stroma, the posterior corneal surface, through the anterior chamber and onto the anterior lens surface.
The wavefront data are used to calculate the light that travels through the eye, from the retina, through the vitreous cavity, onto the posterior lens surface through the natural lens and onto the anterior lens surface. Finally, tilt is calculated between the lens and cornea.
This process is markedly faster than previously, taking just seconds compared with hours. “This process facilitates viewing the eye as a total visual system; that is, as a system of multiple refractive entities,” Dr Kanellopoulos said.
The results in the 25 eyes showed that in patients with a broad range of myopia up to 8 D and significant astigmatism in some patients at 3 months postoperatively, there were highly relevant changes: mean refractive error decreased from −5.06 ± 2.54 D (range, −8.0 to −0.50 D) to −0.11 ± 0.09 D; refractive astigmatism from −1.07 ± 0.91 D (range, −4.25 to 0 D) to −0.15 ± 0.04 D; and topographic astigmatism from −1.65 ± 0.85 D to −0.26 ± 0.11 D.
According to Dr Kanellopoulos, 65% of eyes gained one line of vision and 38% gained two lines. The root mean square changed from 0.25 to 0.35 μm and the contrast sensitivity improved postoperatively. “The visual outcomes were remarkable,” he said.
“This technology has the potential to offer improved and more predictable outcomes through total eye aberration data and ray tracing refraction calculation, and the data are compelling,” he concluded. The data from this study have been subsequently published in peer-reviewed literature.1,2
A. John Kanellopoulos, MD
Dr Kanellopoulos has no financial disclosures related to this content.