In this episode of Interventional Mindset, Arjan Hura, MD, a refractive and cataract surgeon at the Maloney-Shamie-Hura Vision Institute in Los Angeles, CA, discusses ray tracing-guided LASIK and its impact on visual outcomes.
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History and evolution of LASIK
In the early stages of LASIK treatment, procedures were primarily based on simple manifest refractions. These early methods did not consider the “natural hills, valleys, or aberrations” across the entire cornea. Significant innovations have since been made, including corneal topography and tomography which image the front and back surfaces of the cornea, respectively.
Epithelial maps allow for a granular look at the superficial most layer of the cornea, and corneal pachymetry and understanding the concept of residual stromal bed allow for more accurate identification of which patients are and are not good candidates for laser vision correction.
Over the past several decades, LASIK evolved to include various degrees of customization in the form of wavefront-guided, wavefront-optimized, and topography-guided LASIK. Ray tracing-guided LASIK combines the best aspects of these iterations to deliver a highly precise method of vision correction.1
Ray tracing-guided LASIK technology
Alcon’s Sightmap enables comprehensive data collection of the entirety of one’s eye and optical system. Ray tracing-guided LASIK combines subjective refraction, topography, tomography, and wavefront measurements. It also uses laser interferometry to measure the entire eye from anterior to posterior, including axial length and lens position.1
Previous LASIK treatments produced excellent outcomes, but they involved taking a customized wavefront reading of the eye and applying it to a standard eye model. With ray tracing LASIK, the measurements taken create a 3D model of the patient’s eye,1 known as a "digital twin.”
These models are iterated thousands of times to achieve precision before creating a highly personalized treatment. Dr. Hura comments that “it's a level of personalization and customization that really just has never been possible before.”
In the hands of a skilled surgeon, the overall rate of needing a touch-up or enhancement after LASIK is low. However, there are sometimes instances where the prescription may change after surgery. The corneal epithelium can proliferate zonally and in specific areas following treatment—typically centrally after myopic treatments and peripherally after hyperopic treatments.
For most patients, this is usually insignificant and does not affect vision. However, in some cases, it can result in regression that may appear months or even years after the initial treatment. Ray tracing-guided LASIK incorporates predictive capacity technology which theoretically can forecast how the epithelium is likely to remodel after surgery, and assimilate that information into the custom treatment itself, which may help reduce the long-term need for enhancement procedures or touch-ups.
Clinical outcomes and patient candidacy in ray tracing LASIK
Clinical studies show that ray tracing-guided LASIK is an effective procedure. In a study by He et al. (2023), nearly all patients achieved at least 20/20 vision, with approximately 51% achieving 20/12.5 or better 3 months after the procedure. There was no clinically significant increase in higher-order aberrations (HOA) and a marked decrease in spherical aberration was observed.2
In the past, nomograms, or manual software adjustments, were necessary to make small tweaks to treatment plans because each laser functioned differently. Variables such as humidity, room barometric pressure, and even the time a surgeon took to lift a LASIK flap, perform the ablation, and lay it back down could all affect the patient's results.
The use of a custom nomogram specific to the surgeon that takes these variables into account leads to highly accurate outcomes. Sightmap simplifies clinic workflow and reduces reliance on nomograms, thereby decreasing the risk of human error in treatment transcription and selection.
Currently, ray tracing-guided LASIK is approved for patients with a prescription range of -1.00 to -8.00D, with individual-cylinder treatment up to -3.00D. It is not approved for hyperopic and mixed astigmatism patients or photorefractive keratectomy (PRK). Dr. Hura expects that the specifications and indications for the treatment will expand as more datasets come in.
Final thoughts
In conclusion, ray tracing-guided LASIK is safe and effective for correcting myopia, with or without astigmatism. However, it is important to recognize that not everyone is a suitable candidate for LASIK. In some cases, PRK or a phakic intraocular lens (ICL) or even opting for no surgery at all may be the better choice for the patient.
