Data from patients enrolled in prospective studies evaluating treatment of low to moderate myopia with astigmatism using a toric IOL (Visian Toric Implantable Collamer Lens, STAAR Surgical), wavefront-guided (WFG) LASIK, or WFG PRK were compared in a retrospective analysis. Although some differences were identified, all procedures overall were associated with favorable outcomes.
"The laser vision correction techniques provide greater refractive accuracy, whereas patients [in whom the phakic lens had been implanted] show greater gains in best-corrected visual acuity [BCVA] and low contrast visual acuity [LCVA], probably owing to the magnification effect of the [IOL] in this slightly more myopic patient population compared with the subjects treated with laser vision correction," said Dr. Tanzer, staff physician, Naval Medical Center, San Diego. "However, uncorrected visual acuity [UCVA] outcomes were excellent in all groups, and there were no significant differences between them in improvement in night-driving simulator performance.
"To further elucidate potential differences between these modalities and determine their comparative efficacy would require a randomized, prospective study providing matched patient populations," he added. "Hopefully, we will be able to undertake such a project once [this toric lens] receives FDA approval."
6-month visit data
Data from a 6-month visit were available from both studies, including for subsets of patients who completed preoperative and postoperative testing of vision-based performance on a night-driving simulator.
Preoperatively, all three groups were well matched in mean age (29 to 33 years) and mesopic pupil size (~6.5 mm), and the LASIK and PRK groups also were similar compared with each other with respect to mean manifest refraction spherical equivalent (MRSE) (~–5.0 D) and cylinder (~–0.8 D). Reflecting the IOL study inclusion criteria, the phakic lens recipients had a higher mean MRSE (–8.0 D) and cylinder (–1.6 D).
At 6 months after surgery, mean UCVA (logMAR) values among the three groups were –0.08 for the WFG PRK group, –0.06 for the WFG LASIK group, and –0.13 for the IOL group. Mean BCVA (logMAR) values were –0.16 for the WFG PRK group, –0.13 for the WFG LASIK group, and –0.18 for the IOL group.
"There were no significant differences between groups in mean logMAR UCVA or mean logMAR BCVA, which each varied by no more than three letters among the three groups," Dr. Tanzer said.
The mean MRSE results showed a tendency to slight undercorrection in patients who had WFG LASIK (–0.19 D) or WFG PRK (–0.11 D) and slight overcorrection in the IOL group (+0.32 D). Accuracy, however, was better with the laser-based procedures: about 85% of patients undergoing laser treatment had an MRSE ±0.5 D of intended compared with only 67% of patients receiving the IOL.
In all three groups, mean improvements in lines gained of logMAR BCVA (+0.03 to +0.10) were seen. Patients in the IOL and WFG PRK groups also showed improvements in mean logMAR LCVA (+0.11 and +0.03, respectively), whereas a small loss of LCVA was observed in the WFG LASIK group (–0.03). No significant differences were seen between groups regarding these outcomes. The proportions of patients benefiting with improvements in BCVA and LCVA, however, were considerably higher in the IOL group.
"Among the phakic IOL recipients, no patients lost BCVA or LCVA, 96% gained one or more lines of BCVA, and 26% gained two or more lines of LCVA," Dr. Tanzer said. "Only 38% of the WFG LASIK patients and 48% of the WFG PRK patients showed a gain in BCVA, only about 5% of patients in both of the laser vision correction groups gained two or more lines of LCVA, and small proportions of the LASIK and PRK patients experienced losses in BCVA and LCVA."
Night-driving performance was investigated using a commercially available machine (Vision Sciences Research Corp.) that simulates driving on a rural road at 55 mph under conditions with and without rearview mirror glare. Patients press a button when they first detect a road hazard and then again when they can identify the hazard as a business sign, traffic sign, or pedestrian. Each eye is tested independently with best spectacle correction, and results are analyzed based on changes from baseline in the detection and identification distances.
In all three groups, improvements were seen in both the detection and identification distances in testing with and without the glare source.