Wavefront-Guided LASIK Versus Wavefront-Optimized LASIK

Mathmatical modeling and clinical results suggest wavefront-guided LASIK can give better visual results than wavefront-optimized LASIK. Just in the past week, I’ve been asked essentially the same question by a patient from my Santa Barbara office, from my Ventura office, and from my San Luis Obispo office: what is wavefront optimized LASIK and how does it compare to “regular” customized wavefront LASIK? Since it seems to be a popular question now, let me answer it — by looking at both theory and clinical results.

In general, laser vision correction, whether LASIK or PRK, can be peformed as conventional laser eye surgery, wavefront guided laser eye surgery, or wavefront optimized laser eye surgery. For this blog, we’ll focus on LASIK, although everything we’ll talk about could also be applied to PRK.

Conventional LASIK is based on the results of the refraction, the “which is better one or two” test. The patient’s answer tells the doctor which corrective lens best corrects the vision and this prescription is entered into the laser and then applied to the eye during surgery. Obviously, the refraction is ultimately based on the patient’s opinion of the two choices, which makes it subjective and less accurate.

Wavefront-guided LASIK, by contrast, uses a much more precise way to measure the optics of the eye. An invisible, infra-red laser is shined into your eye and then it bounces back off of the retina in the back of your eye. The returning wave of light generated by this laser is distorted and affected by all the focusing elements of the eye on its light flow journey back out through your eye. The distorted wave of light that comes out of your eye is a measurement of light flow thorugh your eye. We call it your “optical fingerprint” — it is a unique-to-you measurement of how your eye affects light flowing through it. Your optical fingerprint is downloaded into the laser and reproduced onto your eye with billionth of an inch tolerances. Because the entire complex distortions in the optical fingerprint are measured and treated, wavefront guided surgery is capable of treating not only nearsightnedness, farsightedness, and astigmatism, but also other aberrations (known as “higher order aberrations”) that are beyond simple nearsightedness, farsightedness, and astigmatism.

There are today various generations of wavefront technology. I personally prefer to use the VISX S4 IR laser which employs Fourier algorithms, iris registration systems, and three dimensional eye tracking to give what I consider to be the state of the art in wavefront guided treatment.

Recently, however, another approach to LASIK has been introduced by the Wavelight Allegretto Laser (Alcon Allegretto): wavefront-optimized LASIK.

The phrase “wavefront optimized” actually can be somewhat confusing to patients. It implies it is a form of wavefront guided LASIK, but it is not. Wavefront-optimized LASIK is in many ways simply conventional surgery, but with modifications based on wavefront modeling and wavefront theory to improve outcomes beyond standard conventional LASIK. With wavefront-optimized LASIK, a refraction is still performed on the patient to generate a precription to be entered into the laser, as is the case with standard conventional surgery. However, standard conventional surgery has been shown to increase a type of higher order optical aberration in the eye callled “spherical aberration.” To counteract this optical error in conventional surgery, a pre-set number of laser pulses are placed into the periphery of the laser ablation to negate the spherical aberration otherwise induced by conventional surgery. In this way, wavefront-optimized surgery simply is an improved version of conventional surgery.

The question has come up how wavefront guided LASIK peformed with the VISX CustomVue excimer laser system compares to wavefront optimized surgery performed with the Allegretto Wave Eye-Q excimer laser system.

In this blog, we’ll look at mathmatical modeling performed by the US Navy to predict the expected outcomes of these two approachs to LASIK: wavefront guided LASIK and wavefront optimized LASIK.

A highly respected colleague of mine, Dr. Steve Schallhorn (who was head of the laser vision correction program for the U.S. Navy’s Top Gun Pilot program at Balboa Naval Hospital in San Diego) recently presented a talk about wavefront guided LASIK versus wavefront optimized LASIK at the annual meeting of the American Society of Catract and Refractive Surgery (ASCRS). His talked centered around mathmatical modeling of the results expected from conventional LASIK, wavefront optimized LASIK, and wavefront guided LASIK, using the Navy’s modeling system.

Dr. Schallhorn pointed out that it is well known that conventional LASIK does increase the distortions in the optics of the eye known as “higher order aberrations” that we discussed earlier. These are distortions beyond simple nearsightedness, farsightedness, and astigmatism. The particular type of higher order aberration increased by conventional surgery is spherical aberration. An increase in spherical aberration has been associated with problems with night vision and contrast resolution, particularly under low light conditions.

With wavefront optimized LASIK, Dr. Schallhorn pointed out that the U.S. Navy did notice that there was no increase in spherical aberration (an improvement upon conventional LASIK), but also pointed out that the treatments still were based on a patient’s refraction. In this way, wavefront optimized LASIK met its design goal of providing a conventional, refration based treatment, but without an increase in spherical aberration.

True wavefront guided LASIK, by contrast, rather than simply targeting a lack of increase in spherical aberration, by design actually target an elimination of all higher order aberrations. Wavefront guided LASIK aims to fully correct the optical fingerprint — the complete and complex measurement of all the higher order aberrations including, but not limited to, spherical aberration. Wavefront guided LASIK, unlike wavefront optimized LASIK, therefore is not designed simply just to avoid an increase in only one specific higher order aberration, spherical aberration — rather it is designed actually to address all higher order aberrations, including spherical aberration.

Given the basic different designs of the three approaches, Dr. Schallhorn then presented an objective mathmatical modeling system which looked at correcting vision with conventional LASIK, wavefront optimized LASIK, and wavefront guided LASIK. As expected, in the modeling system, conventional LASIK increased higher order aberrations and wavefront optimized LASIK induced fewer higher order aberrations, but wavefront guided LASIK resulted in even fewer higher order aberrations.

The U.S. Navy then tested this mathmatical model and found the model’s results were verified in clinical experience: wavefront guided LASIK laser vision correction resulted in fewer higher order aberrations remaining in the patient’s visual system than wavefront optimized LASIK. Both were better in the real world than conventional LASIK.

Dr. Schallhorn then asked the theoretical question of whether it actually matters in the real world what someone’s higher order aberrations are. He presented a study done by the U.S. Navy looking at their top-gun pilots with the best natural (non-surgical) vision. Even in this elite group of pilots, who were born with outstanding vision, the lower their level of their higher order aberrations, the better their contrast sensitivity and visual performance. Having the lowest possible higher order aberrations did, in fact, make a difference in the real world — particualrly to a high performance pilot. For this reason, the best technology would aim to provide the lowest possible higher order aberrations in its treatment outcomes.

Dr. Schallhorn then presented the clinical results of another respected colleague, Jack Holladay, M.D. Dr. Holladay performed a study looking at VISX CustomVue Wavefront-guided LASIK versus Allegretto Eye-Q Wavefront-optimized LASIK and found fewer higher order aberrations in the the VISX Wavefront-guided LASIK patients. Dr. Holladay also found superior contrast resolution in the clinical visual performance results of VISX Wavefront-guided LASIK patients compared to the Allegretto Wavefront-optimized LASIK patients.

Because mathmatical modeling predicts that wavefront-guided LASIK will outperform wavefront-optimized LASIK and because clinical results confirm this difference, Dr. Schallhorn concluded his talk by noting that in the U.S. Navy Top-Gun Pilot Program, Navy surgeons will use wavefront guided LASIK rather than wavefront-optimized LASIK.

I agree with this conclusion and I personally also use wavefront guided LASIK and wavefront guided PRK on essentially all my patients, rather than either conventional LASIK/PRK or wavefront optimized LASIK/PRK.

In my next blog, we’ll look at some additional clincial results which supports the mathmatical modeling data that Dr. Schallhorn presented showing that VISX CustomVue wavefront guided LASIK will outperform Allegretto Wave Eye-Q wavefront optimized LASIK.

Wavefront-Guided LASIK Versus Wavefront-Optimized LASIK

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