Study: Final results favorable for both SBK, ASA

January 1, 2008

Advanced surface ablation and sub-Bowman's keratomileusis (SBK) were compared in a randomized, prospective study enrolling 200 patients who underwent bilateral surgery using the same procedure in both eyes. At 1 year, predictability, visual acuity, quality of vision, and safety outcomes were excellent. SBK had significantly faster visual recovery.

Key Points

"Based on previous reports, we assumed when we started this study the results would favor the surface procedure," said Dr. Schallhorn, currently in private practice in San Diego and medical director for Optical Express. "However, using the technology we did, we found no significant differences in any of our outcome parameters at the end of our follow-up."

The study was undertaken at the Naval Medical Center, San Diego, where Dr. Schallhorn and David J. Tanzer, MD, performed all of the surgeries. Two hundred patients were randomly assigned to undergo bilateral treatment with ASA or SBK. The ASA procedure was performed using an epithelial brush (Amoils Epithelial Scrubber, Innovative Excimer Solutions Inc.) to remove the epithelium. The femtosecond laser (IntraLase, Advanced Medical Optics) was programmed to create a 9.1-mm, 100-μm flap in the SBK eyes (actual 96 μm). All of the ablations were performed with a custom laser vision correction system (Star 4 CustomVue, Advanced Medical Optics/VISX) using the Fourier algorithm but without iris registration. The ablation zone had a 6-mm optical zone with a transition zone to 8 mm.

Postoperative care for the ASA eyes included placement of a bandage soft contact lens and topical treatment with tetracaine, an antibiotic, and a corticosteroid, which was tapered over 2 months. Eyes treated with SBK were placed on a 1-week course of topical antibiotic and corticosteroid treatment.

The two study groups were well-matched preoperatively. Mean manifest refraction spherical equivalent (MRSE) in both groups was about –3 D. Across the entire population, preoperative sphere ranged from –0.25 to –5.75 D and cylinder ranged up to –2.50 D. About 85% of eyes in each group were seen at 12 months.

Visual recovery was rapid in the SBK eyes, whereas it took until about 3 months for the ASA group to catch up. In the SBK group, uncorrected visual acuity (UCVA) of 20/16 or better was achieved in 77% of eyes at 1 week and in 87% of eyes at 1 month. Only 10% of ASA eyes had UCVA of 20/16 or better at 1 week. The proportion of ASA eyes with UCVA of 20/16 or better increased to 59% at 1 month and to 81% at 3 months. At 1 year, 88% of eyes in both groups had UCVA of 20/16 or better and about half were seeing 20/12.5 or better unaided.

Accuracy and predictability were excellent. At 1 year, mean MRSE was close to emmetropia in both groups (SBK, –0.04 ± 0.23 D; ASA, –0.03 ± 0.27 D) and was within 0.50 D of target in 98% of SBK eyes and 94% of ASA eyes.

"Almost three-fourths of SBK and ASA eyes had an MSE that was ±0.25 D of attempted. Emmetropia was our refractive target and the data show we hit it very well," Dr. Schallhorn said.

MSE outcomes also supported the decision to apply no nomogram adjustment for the ASA procedure, he added.

Safety and visual quality outcomes also were similar in the two groups. The mean change in best-corrected visual acuity (BCVA) from baseline showed a small similar gain in both groups at 12 months, with no eyes losing 2 or more lines of BCVA and only a few eyes (SBK 1.7%, ASA 2.8%) losing a single line.