The ‘new’ LASIK

An eye undergoing the IntraLase FS laser procedure, which is used in many SBK surgeries
Source: Howard Kornstein, M.D.

Ophthalmologists are familiar with LASIK’s “wow” factor, or the procedure’s ability to yield a near-immediate experience of excellent visual correction. While patients are often able to see clearly the day after LASIK, a new study details the benefits of certain versions of LASIK over PRK.
The study, published in the June 2009 issue of Ophthalmology, pitted thin-flap LASIK (termed sub-Bowman keratomileusis or SBK) against PRK.
“The SBK eyes were able to recover visual acuity and to return to functioning vision more quickly than the PRK patients, with 100% of the SBK eyes at legal driving vision (20/40) at day 1,” according to lead study author Stephen G. Slade, M.D., Houston.
Not all of the results favored SBK. “There was a greater loss of corneal sensitivity in the SBK flaps than in the PRK eyes through 6 months,” Dr. Slade noted. By six months post-op, there were no statistical differences between SBK and PRK eyes.
However, the immediate benefits of SBK are important to consider in a world where quick fixes are appreciated.

SBK vs. PRK

Dr. Slade performed a prospective, contralateral, randomized study on 50 patients (100 eyes) enrolled at two sites. Each patient underwent PRK in one eye and SBK in the contralateral eye.
Patients underwent myopia correction (of –2 to –6 D), with astigmatism up to –3.50 D.
The IntraLase FS Laser (Abbott Medical Optics, Santa Ana, Calif.) was used to make 100-micron (intended), 8.5-mm flaps in the SBK group. Ethanol-assisted PRK was performed in the other group. Both groups underwent laser correction with the LADARVision 4000 Excimer Laser (Alcon, Fort Worth, Texas).
Differences at 1 month were stark. “The UCVA at the 1-month postoperative visit showed 88% of the SBK eyes at 20/20 or better compared with 48% of the PRK eyes,” Dr. Slade reported.
Differences, however, began to disappear at three months (although there were some), and dissolved altogether at six months.
“Seventy percent of SBK eyes were 20/16 or better compared with 64% of PRK eyes at 3 months,” Dr. Slade reported. “At 6 months after surgery, there was a further equalization with 94% of the PRK eyes and 92% of the SBK eyes achieving a UCVA of 20/20 or better.”
Best-corrected vision was also affected in a similar manner in the groups. “The BSCVA results showed a similar trend at 1 and 3 months, with 42% of the SBK group gaining 1 line or more of vision compared with 16% in the PRK group at 1 month,” Dr. Slade reported. “Forty-two percent of the PRK group lost 1 line or more of vision, compared with 22% losing 1 line in the SBK group.”
At three months, 57% of the SBK eyes experienced an improvement of one line or more of BSCVA compared with a statistically similar 53% in the PRK group. At 6 months, 62% of SBK eyes gained a line or more, in comparison to 56% in the PRK group.
Subjective questionnaires also found 88% of participants reporting PRK as more painful at day three, although at one week this finding decreased markedly (to 49%, with 49% reporting both eyes felt the same). Eyes experienced virtually the same amount of comfort by six months.
“The results show that even with modern pharmaceutical therapy to manage pain and discomfort, patients in this study overwhelmingly found their PRK eye to be more painful, particularly in the first week, but even past the 1-month mark,” Dr. Slade reported.
Eyes were also reported to be drier with PRK at each follow-up visit through six months.
Satisfaction with vision was studied and showed some remarkable differences. “At the 1- and 3-day and 1-week visits, patients showed a preference for their SBK eye by a factor of 20:1,” Dr. Slade reported. “At the 1-month visit, the ratio was 10:1, and then the ratio was approximately 2:1 at 3 months after surgery.”
Dr. Slade went a step further, analyzing biomechanical results for both SBK and PRK eyes. “Lower CH [corneal hysteresis] and CRF [corneal response factor] values theoretically are suggestive of a biomechanically weaker cornea,” Dr. Slade reported. “The CH decreased after both SBK and PRK, which may suggest that there was no biomechanical advantage to the surface ablation technique. The same was true with the CRF results, with a theoretic equal biomechanical weakening seen in both the SBK and PRK eyes.”
Finally, Dr. Slade emphasized that although over time PRK and SBK results are much more comparable, the early period of recovery is important to consider.
“Proponents of surface procedures argue that it is unfair to compare the results between a flap-based and surface ablation procedure before the 3-month visit,” Dr. Slade noted. “However, they may be missing what is important from the patient’s perspective.
Sub-Bowman keratomileusis would seem to be more practical for the patient with less pain, quicker visual recovery, fewer medications, and an overall superior experience.”
William B. Trattler, M.D., director, Cornea, Center for Excellence in Eye Care, Miami, said that using the IntraLase FS Laser and a similar technique, he is much happier with LASIK surgery than he was a number of years ago. In fact, he switched back to LASIK as his preferred refractive surgery technique from surface ablation.
“The reason I left LASIK originally was because of an increased risk of ectasia, worse quality of vision, and a risk of complications with metal microkeratomes,” Dr. Trattler said. “Almost two and a half years ago, I went back to LASIK with the IntraLase because of fewer biomechanical changes with thinner IntraLase flaps and other benefits.”
Essentially, Dr. Trattler said, performing thin-flap LASIK with the IntraLase resolved all his previous LASIK concerns.

Editors’ note: Dr. Slade has financial interests with Abbott Medical Optics (AMO, Santa Ana, Calif.) and Alcon (Fort Worth, Texas). Dr. Trattler has financial interests with AMO.

Contact information

Slade: sgs@visiontexas.com
Trattler: 305-598-2020, wtrattler@gmail.com