Customized ablation valuable even without iris registration function

October 15, 2008

Outcomes of wavefront-guided LASIK performed using a proprietary excimer laser (STAR S4 IR, Advanced Medical Optics) are superior to those achieved when the laser is used for conventional LASIK, and the benefits associated with the wavefront-guided procedure appear to persist even when the iris registration function cannot be used.

Key Points

She discussed results from a study comparing refractive, visual acuity, contrast and glare sensitivity, and wavefront outcomes of groups of patients undergoing LASIK using a wavefront-guided technique with iris registration (WFG-IR) in 129 eyes, wavefront-guided surgery without IR (WFG-no IR) in 14 eyes, or a conventional ablation (74 eyes).

Compared with conventional LASIK, the WFG-IR group had significantly less astigmatism and less induced higher-order aberrations (HOAs), as well as significantly better contrast and glare sensitivity. No significant differences were found comparing the WFG-no IR group with the conventional LASIK eyes. Dr. Suzuki-Judge noted, however, that finding may be due to inadequate statistical power given the small number of eyes in the WFG-no IR group.

The eyes included in the study were identified from a review of the records of 396 LASIK procedures performed in 199 patients at Inouye Eye Hospital between November 2006 and June 2007. In all eyes, LASIK flap creation was performed using a proprietary microkeratome (MK-2000, Nidek).

The three study groups were similar in their gender distribution (40:60 male:female) and mean age (32 to 34 years). Mean preoperative spherical equivalent (SE) in the conventional LASIK group (–6.29 D) was significantly higher than in the wavefront-guided groups treated with IR (–4.85 D) and without IR (–4.96 D). Mean preoperative astigmatism was about –1 D in all three groups.

Comparisons of UCVA

No significant differences were observed across the three groups in uncorrected visual acuity (UCVA) results. A greater proportion of patients in the WFG-IR group achieved higher levels of UCVA, however. In the WFG-IR, WFG-no IR, and conventional groups, rates of UCVA 20/20 or better were 90.2%, 92.9%, and 90.0%, respectively, whereas the proportions of eyes in which UCVA of 20/12.5 or better were achieved were 72.5%, 64.3% and 61.5%, respectively.

Mean SE at 3 months was 0.02 D in the WFG-IR group, 0.10 D in the WFG-no IR group, and 0.09 D in the conventional group, with no between-group significant differences in those outcomes. Mean astigmatism, however, was significantly less in the WFG-IR group compared with the conventional group, 0.11 versus 0.18 D, respectively, and it was even lower in the WFG-no IR group (0.05 D). Not enough data points existed to compare the latter outcome to the other groups, however.

Total HOA root mean squared increased in all groups, but at 3 months, the change from baseline was significantly less in the WFG-IR group compared with the conventional group, 0.16 versus 0.31 μm, respectively. The results of the WFG-no IR group again were very similar to the WFG-IR group, with a mean increase of 0.17 μm.

Contrast sensitivity was best in eyes treated with WFG-IR LASIK. When the results were analyzed for change from the preoperative level, the latter patients had an improvement in contrast sensitivity at 3 months, whereas the conventional group had a loss, and the difference between groups was statistically significant. Similarly, outcomes of glare sensitivity testing were better after surgery compared with before in the WFG-IR group and worsened at most spatial frequencies in the conventional LASIK group. The difference between these two groups also was statistically significant. Glare sensitivity results in the WFG-no IR group were very similar to the WFG-IR group.