Ray Tracing–Guided LASIK

Patient-specific optical modeling may improve refractive consistency, reduce enhancements, and refine LASIK treatment selection.

Last year, I picked up a new obsession: golf. Like many beginners, I assumed the key to playing golf better was hitting the ball farther. I spent hours swinging harder and chasing the perfect drive before realizing I had the wrong goal. Golf is not won by the longest drive. It is won by consistently posting the lowest score or, in my case, lowering my handicap.

I began to wonder whether this lesson also applies to refractive surgery. In my workflow, planning topography-guided LASIK with Contoura Vision (Alcon) using the Phorcides Analytic Engine (Phorcides) required multiple diagnostic and planning steps. The WaveLight Plus workflow, which incorporates InnovEyes Sightmap (both from Alcon), consolidated some of that process. Would the streamlined workflow also reduce my enhancement rate and improve the overall patient experience?

For years, 20/10 uncorrected distance visual acuity (UDVA) has been celebrated as the ultimate LASIK outcome. I still enjoy seeing a patient read the 20/10 line, but high-contrast distance acuity does not represent the entire patient experience. Is achieving 20/10 UDVA in the most eyes the same as satisfying the most patients? I am no longer sure. That question became my new scorecard (Figure 1).

What I Saw in Practice

During the past several years, I have treated patients with wavefront-optimized LASIK, topography-guided LASIK planned with Phorcides, and, most recently, WaveLight Plus ray tracing-guided LASIK. These were sequential practice cohorts, not randomized or contemporaneous comparison groups. Differences in patient selection, follow-up duration, testing protocols, workflow, and clinical experience limit direct comparisons among them.

Topography-guided LASIK frequently achieved 20/15 UDVA and some of the sharpest 20/10 results in my practice. Patients often described excellent visual clarity.

After the US FDA approved the WaveLight EX500 laser system with InnovEyes Sightmap for WaveLight Plus LASIK in 2025, I cautiously adopted the treatment and adjusted case selection as my experience grew (Figure 2).

In routine clinical practice, my patients' postoperative UDVA clustered at 20/20 and 20/15 (Figure 3). My staff and I documented fewer 20/10 eyes than some published series; our technicians did not always test to failure at that level, however, and we did not standardize chart type and lighting as a clinical trial would. Routine testing therefore could have underestimated the proportion of eyes achieving 20/10 UDVA.

The largest difference I observed was in my enhancement rate, which was 3.24% during my topography-guided period and 0.26% for my first 2,300 WaveLight Plus treatments.

From Population-Based Assumptions to Patient-Specific Modeling

Progressive Personalization

My experience changed how I view the evolution of excimer laser treatment planning. Earlier approaches relied largely on the manifest refraction. Wavefront-guided treatments incorporated measured ocular aberrations, wavefront-optimized treatments were designed to preserve corneal asphericity and limit induced spherical aberration, and topography-guided treatments incorporated anterior corneal topography. Phorcides added modeled estimates of posterior corneal and lenticular astigmatism and calculated how a topography-guided ablation could affect sphere and cylinder. Ray tracing extended this progression by modeling how light travels through the measured optical structures of the individual eye.

Building a Patient-Specific Eye Model

WaveLight Plus combines biometric, corneal, and wavefront measurements to construct a patient-specific optical model. The software traces light rays through that model and iteratively adjusts the proposed ablation profile to optimize retinal focus.

Population-based assumptions and schematic eye models remain useful, but no single model can represent every combination of axial length, anterior chamber depth, corneal shape, and lens position. Patient-specific modeling incorporates more of the measured anatomy of the individual eye, although its accuracy still depends on the quality of the measurements and the assumptions built into the model.

Where Each Tool Fits

Ray tracing has not replaced the other technologies in my refractive toolbox. Instead, it has changed how I distribute cases. My goal is to select the approach that best matches a given patient's anatomy, refractive error, optical quality, and diagnostic data.

Ray Tracing as the Primary Pathway

WaveLight Plus is currently my preferred treatment for routine myopic LASIK in phakic eyes when high-quality Sightmap data can be obtained. This strategy accounts for approximately 90% of the LASIK procedures I perform.

Among routine phakic patients with myopia, I suspect that the incremental benefit of whole-eye modeling may be greatest among those who have large pupils. Higher-order aberrations become more consequential as the pupil enlarges, and ray tracing can incorporate optical contributions that anterior corneal topography alone does not measure. This remains a clinical hypothesis rather than a demonstrated advantage in the data presented here.

When the Scans Fall Short

The Sightmap quality indicators help my technicians determine whether each acquisition is adequate. Occasionally, uniformly high-quality scans cannot be obtained despite repeated attempts. Often, these eyes have very large or very small pupils. When the data do not meet the platform's quality criteria, I select another form of treatment rather than proceed with a compromised dataset.

Roles for Topography-Guided and Wavefront-Optimized LASIK

When high-quality Sightmap data cannot be obtained, I choose between topography-guided and wavefront-optimized LASIK based on the reason for scan failure and the characteristics of the eye. I typically prefer wavefront-optimized LASIK if the eye is hyperopic or has an unusually large or small pupil. I reserve topography-guided treatment for certain eyes with an irregular or complex cornea, enhancement and rehabilitation cases, and pseudophakic eyes. In other words, I match the treatment to the patient (Figure 4).

Candidacy Still Comes First

Ray tracing has changed which patients remain LASIK candidates in my practice, but it does not override the fundamental requirements for safe corneal surgery. I continue to recommend phakic IOLs or refractive lens exchange when the patient's age, refractive error, corneal anatomy, ocular surface, or visual goals favor a lens-based procedure. For patients who are candidates for corneal surgery, patient-specific modeling provides another means of refining treatment.

Tightening the Landing Zone

In my experience, ray tracing is not raising the ceiling of best-case visual acuity. Its more relevant contributions are a narrower distribution of outcomes and fewer outliers. Wavefront-optimized ablation, topography-guided ablation, and ray tracing have each added information to the planning process. The difference in enhancement rate I observed with ray tracing is consistent with a tighter landing zone, but this finding requires confirmation through a comparison with standardized follow-up and similar patient populations.

Every avoided enhancement reduces chair time and spares the patient and surgeon an additional procedure. That outcome matters even when a patient's initial UDVA is not 20/10.

A More Integrated Workflow

Planning a topography-guided treatment with Phorcides requires scans on two devices, data transfer to a separate planning platform, and manual entry into the laser. WaveLight Plus consolidates diagnostic acquisition, treatment planning, and data transfer into a more integrated workflow. This may reduce opportunities for transcription errors and make the process more reproducible, but it does not replace surgeon judgment or prove that the treatment itself is superior.

Colleagues frequently told me that they appreciated the results of topography-guided treatment but were reluctant to adopt the associated planning workload. By incorporating more of the calculation into the platform, the ray tracing workflow may make patient-specific ablation more feasible for surgeons who do not perform a high volume of LASIK procedures.

No Separate Nomogram-Yet

After 2,300 treatments, I unexpectedly have not yet developed a separate nomogram for WaveLight Plus. With earlier workflows, I typically analyzed the first several hundred or 1,000 eyes and adjusted the treatment plan based on the results. Thus far, I have not found such an adjustment necessary.

A Better Scorecard

Golf is not won by the longest drive, and LASIK success should not be defined solely by the number of eyes that achieve 20/10 UDVA. A more meaningful scorecard pairs high-contrast acuity with refractive accuracy, the surgeon's enhancement rate, patients' visual symptoms, and patient-reported outcomes. It should also ask whether patients would choose LASIK again and recommend it to others (Figure 5).

Perhaps the best outcome is a patient who loves their vision enough to forget they ever had surgery.

Now if only ray tracing could improve my putting.