Pulse technology boosts all-laser PRK for one-step, no-touch ablation

March 1, 2017

A transepithelial PRK (TransPRK) procedure (SmartSurface, Schwind eye-tech-solutions) provides the benefits of one-step, no-touch surface ablation plus rapid visual recovery, said Diego de Ortueta, MD.

Reviewed by Diego de Ortueta, MD

A transepithelial PRK (TransPRK) procedure (SmartSurface, Schwind eye-tech-solutions) provides the benefits of one-step, no-touch surface ablation plus rapid visual recovery, said Diego de Ortueta, MD. 

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The technique--performed with an excimer laser system (AMARIS) and pulse technology (SmartPulse Technology [SPT], both Schwind eye-tech-solutions)--is able to create a smoother corneal surface. With the novel pulse technology, the laser spots are delivered based on a three-dimensional fullerene structural model of the cornea that accurately represents the cornea’s curved surface and allows spots to be placed closer together, particularly in the periphery.

“The difference in smoothness can be seen on electron micrographs,” said Dr. de Ortueta, medical director, Aurelios Augenzentrum, Recklinghausen, Germany. “Laboratory bench testing shows that compared with the original software for [the excimer laser], SPT reduces surface roughness by about 60%, from 749 to 272 nm local standard deviation.”

 

Diving deeper

Results of a retrospective study comparing two consecutive groups of 125 eyes each that underwent TransPRK with or without pulse technology showed the benefit of the procedure, Dr. de Ortueta noted. Predictability of the refractive outcome was equally good in both groups as was safety, with no eyes losing 2 or more lines of Snellen visual acuity. At the time of bandage contact lens removal on postoperative day 4, however, visual acuity was 20/25 or better in 80% of patients in the SmartSurface group compared with just 55% of those treated without the new pulse technology.

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“In addition, the corneas of the eyes in the SmartSurface group appeared clearer postoperatively,” he said.

The idea of TransPRK has always been attractive to refractive surgeons because of the elegance and simplicity of removing the epithelium with the excimer laser instead of by mechanical or chemical debridement, Dr. de Ortueta noted.

Absence of a systematized “plug-and-play” option for performing the procedure hampered its adoption, but that obstacle was overcome in 2009 when the manufacturer implemented single-step TransPRK for the excimer laser.

“With this technique, the laser fires the aspheric PRK treatment profile first and then switches to a defined-depth radial PTK mode for aspheric epithelial ablation,” Dr. de Ortueta explained.

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“The ORK-CAM software of the laser compensates for the slight differences in photoablative rates of the stroma and the epithelium, and the applied defined epithelial thickness profile is based on literature values and mean epithelial profiles of large-based populations so that it is thinner at the center and thicker at the periphery,” he said. “Treatment without this aspheric ablation would remove about 10 μm of stromal tissue and induce a myopic-like correction of approximately -0.75 D.”

The software also takes into account the greater loss of energy for pulses delivered at the periphery and the change of the corneal curvature during the treatment.

Preferred technique

 

Preferred technique

Dr. de Ortueta said that TransPRK has become his excimer laser procedure of choice for refractive surgery, replacing LASIK.

“Epithelial healing and visual recovery occur much faster . . . compared with traditional PRK or LASEK, and while the healing process after [TransPRK] still takes longer than after LASIK or femto-LASIK, most patients will achieve binocular visual acuity of 20/25 or better by day 4,” he said. “Compared with LASIK, however, the . . . procedure has many advantages.”

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Outlining its benefits, Dr. de Ortueta explained that it allows a nearly perfect correspondence between the topography and the cornea. In addition, it avoids flap complications, related activity restrictions for the patient, and the need for a microkeratome or femtosecond laser.

“We still offer LASIK to all individuals who would be appropriate candidates, but we find that the idea of a flapless procedure is very appealing to patients,” Dr. de Ortueta said.

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TransPRK also induces less biomechanical changes and has a lower risk for causing ectasia compared with LASIK.

In addition, surgical time is faster. For example, laser treatment time for a 4 D myopic correction is only 40 seconds, which makes fixation easier for the patient.

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There is the potential for haze after TransPRK as there is with any surface-ablation procedure, Dr. de Ortueta noted.

“We have now treated more than 700 cases with this new technique,” he said. “Even though we do not use mitomycin-C on virgin eyes, we have observed a <1% incidence of clinical significant haze.” 

 

Diego de Ortueta, MD

E: ortueta@gmx.de or diego.de.ortueta@augenzentrum.org

Dr. de Ortueta is a consultant to Schwind eye-tech-solutions.