July 2017

 

REFRACTIVE

 

Refractive editor’s corner of the world
Wavefront-guided vs. wavefront-optimized laser treatments


by Michelle Stephenson EyeWorld Contributing Writer

 

 

Compared to refractive surgery 15 years ago, modern day refractive surgery has evolved into a specialty that utilizes advanced diagnostics to determine which technology is best for each situation. The most common refractive surgery procedures involve corneal laser vision correction or lens replacement. The technology choices in laser vision correction have grown significantly, much like our choices in lens replacement implant technology. When a 30-year-old myope utilizes his or her best optical correction and has nighttime glare in combination with higher order aberrations, a wavefront-guided treatment (WFG) is a quality option. If a patient has had previous refractive surgery and had visually significant higher order aberrations induced, a WFG treatment can be very helpful. For all other situations, we offer the patient wavefront-guided or wavefront-optimized (WFO) PRK, LASIK, or SMILE. In this article, William Trattler, MD, Michael Greenwood, MD, Michael Gordon, MD, and A. John Kanellopoulos, MD, discuss wavefront-guided and wavefront-optimized technology and how they use them to treat their patients. Both have a place, and in our center, we utilize both technologies. Thank you to our contributors for sharing their experience, knowledge, and opinions. 

Vance Thompson, MD,
Refractive editor


Both provide good outcomes with minimal induction of higher order aberrations


The wavefront measurement principle with a Tscherning device, in which wavefront deviation data are derived from projected patterns on the retina, imaged, and analyzed
Source: A. John Kanellopoulos, MD

Wavefront-guided and wavefront-optimized laser treatments offer advantages over traditional laser treatments. In the past, many patients had night vision complaints after traditional LASIK. These complaints are rare with the more advanced algorithms.
“Wavefront-guided and wavefront-optimized are two different algorithms for trying to provide the best quality vision to patients desiring laser vision correction with LASIK and PRK,” said William Trattler, MD, Miami.
Michael Greenwood, MD, Fargo, North Dakota, agreed. “Wavefront-guided and wavefront-optimized are great treatment options in many patients. Wavefront-guided will reduce pre-existing higher order aberrations, while wavefront-optimized will minimize the induction of new higher order aberrations. Both are superior to conventional treatments, which are more likely to induce higher order aberrations following refractive surgery,” he said.

Wavefront-guided

According to Dr. Trattler, wavefront-guided treatments use measurements of each patient’s unique optical pathway to design a treatment that will correct the patient’s refractive error, including any mild irregularities in the optical pathway. “It’s taking an individualized scan of each eye, and the software develops a customized treatment based on the patient’s unique findings,” he explained.
It’s an excellent treatment for patients who have a clear lens and pre-existing higher order aberrations, Dr. Greenwood said. “However, it might not be the best option for someone who is in his or her 50s and has some lens changes; the wavefront is picking up aberrations that are from the lens rather than from the cornea. You would be treating the higher order aberrations in the lens,” he said.
According to Michael Gordon, MD, San Diego, “The thought behind wavefront-guided treatments is that if we can measure wavefront aberrations with a reliable wavefront sensor and we have a scanning spot laser that has a tracker, we would be able to correct wavefront errors and make quality of vision better. That’s where wavefront came about. However, unless you get above 0.4 µm of RMS higher order aberrations, you don’t see better results than with wavefront-optimized.”
The problem with wavefront- guided treatments is that they are dynamic. “In other words, they change with pupil diameter, they change with accommodation, and they change with age. I think most people in the United States, other than those using a VISX platform [Johnson & Johnson Vision, Santa Ana, California], do not use wavefront-guided. Surgeons using a WaveLight laser [Alcon, Fort Worth, Texas] typically do not use wavefront-guided treatments as the initial treatment, particularly now that we’ve got topography-guided,” Dr. Gordon said.

Wavefront-optimized

According to Dr. Gordon, wavefront- optimized treatment, historically, was developed because surgeons realized that when energy was delivered to the periphery of the cornea, particularly with the scanning spot laser, some energy was lost. “One reason for this is the cosine effect: Because we’re coming tangential to the cornea, a certain percentage of the energy is reflected and not absorbed. Second, because the round beam is on a curved surface, coming again tangential, it becomes ovalized. The energy characteristics change, meaning the energy density changes because now it’s a bigger spot size but the same energy. Now we’re delivering less energy to any given spot. Because of those two characteristics, we weren’t getting as much energy as we needed delivered to the peripheral cornea, which basically generated more spherical aberration than one wanted. People with big pupils, in particular, would have night glare issues. Wavefront optimization was a way to deliver more energy to the peripheral cornea to compensate for the loss in a scanning spot laser,” he explained.
Dr. Trattler noted that wavefront-optimized treatments were developed after evaluating postoperative LASIK results and making adjustments in the algorithm for treating and reshaping the eye to improve the quality of vision by improving the transition zone of the treatment, which is the area between the optical zone and the rest of the cornea.
“One of the arguments regarding use of wavefront-optimized over wavefront-guided treatments is that normal eyes do not usually have higher order aberrations. Therefore, it would not make sense to employ wavefront-guided treatment, which could induce higher order aberrations due to capture and/or delivery error,” said A. John Kanellopoulos, MD, professor, New York University, and medical director, Laservision.gr Institute, Athens, Greece. “Potential parameters that may induce higher order aberrations include the LASIK flap, decentration of the excimer ablation, and irregularities in the ablation.”
The use of the femtosecond lasers for flap creation has reduced wavefront deviations for most LASIK patients. The reduction in flap-related aberrations may be the strongest indication for the use of femtosecond lasers in flap creation in LASIK.
Laser centration is also a concern. The latest laser trackers have higher frequencies and therefore faster response times. “Centration, especially for myopic ablations, has been more important than matching pupil size in determining quality of vision in mesopic and scotopic pupils. A decentration of more than 100 μm in myopic ablations starts to become significant and may induce mesopic and scotopic aberrations,” Dr. Kanellopoulos said.

Conventional laser treatments

Wavefront-guided and wavefront- optimized treatments are not ideal for all patients, so there is still a place for conventional laser treatments.
“One of the challenges is that in patients who are pseudophakic or who have irregular corneas, it is sometimes difficult to capture a high quality wavefront measurement. It depends on the wavefront technology,” Dr. Trattler said. “For example, the original VISX device, called WaveScan, has difficulty obtaining a high quality capture in pseudophakic patients. In comparison, a newer technology called iDesign [Johnson & Johnson Vision] measures five times more points, so it provides higher density of measuring. The iDesign can capture higher quality wavefront images, and can provide an accurate measurement, as well as a non-subjective refraction, in patients who are pseudophakic.”
“It’s nice for surgeons to have a lot of tools in their toolbox so that they can fit the technology to the patient rather than fitting the patient into the technology,” Dr. Greenwood said. “For most eyes, both treatments are going to be good. For patients who have a lot of pre-existing higher order aberrations, wavefront-guided treatment is a better option. But in general, they both provide good outcomes with minimal induction of higher order aberrations, which means good quality of vision following the procedure.”

Editors’ note: Dr. Gordon and Dr. Kanellopoulos have financial interests with Alcon. Dr. Trattler has financial interests with Alcon, Bausch + Lomb (Bridgewater, New Jersey), and Johnson & Johnson Vision. Dr. Greenwood has no financial interests related to his comments.

Contact information

Greenwood
: Michael.greenwood@vancethompsonvision.com
Gordon: mgordon786@gmail.com
Kanellopoulos: ajkmd@mac.com
Trattler: wtrattler@gmail.com

Wavefront-guided vs. wavefront-optimized laser treatments Wavefront-guided vs. wavefront-optimized laser treatments
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