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Wavefront valuable for LASIK enhancements, surgeon says
In a study of complicated cases, UCVA and BCVA improved and visual disturbances and wavefront aberrations decreased after WASCA enhancement.
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Severe visual disturbances and complications stemming from previous refractive surgeries were successfully corrected with wavefront-guided LASIK enhancement, a surgeon reported.
“We were exceedingly successful in helping these patients who had no other alternative and who were desperate,” Dan Z. Reinstein, MD, MA (Cantab), FRCSC, of the London Vision Clinic, told Ocular Surgery News. “Currently, the primary role for wavefront sensing will be for applications of this kind.”
Dr. Reinstein performed wavefront-guided surgery at the London Vision Clinic on 15 highly aberrated eyes of 13 patients with “serious debilitating visual disturbances” from June to November 2002.
In postoperative testing, Dr. Reinstein noted a significant improvement in best-corrected visual acuity (BCVA), and uncorrected visual acuity (UCVA), a significant lowering of higher-order aberrations and an improvement in symptoms from preop levels.
“We were able to improve vision significantly with the WASCA (Wavefront Supported Corneal Ablation) aberrometer coupled to the MEL 70 G-scan excimer laser from Carl Zeiss Meditec,” he said.
Dr. Reinstein said that “the greatest utility now for wavefront sensing is not going to be for primary procedures but rather enhancements and the correction of complications.”
“We are becoming more and more competent at correcting refractive errors without inducing significant aberrations,” he said. “Having wavefront sensor feedback to iterate the treatment of regular spherocylindrical profiles has been the major contribution of wavefront sensing to treatment of unoperated eyes.
“As unoperated eyes have so little in the way of higher-order aberrations anyway, and as comparatively much larger amounts of aberrations are induced by current spherocylindrical treatments, wavefront-guided custom primary treatments will be generally as effective as well-designed optimized profiles,” he said.
“The MEL 80 possesses a prolate optimization function that compensates for epithelial and biomechanical factors that lead to the induction of aberrations in ordinary spherocylindrical treatments,” Dr. Reinstein said.
Patient profile
The prospective pilot study included patients with serious visual problems resulting from laser thermal keratoplasty (LTK), PRK and LASIK.
“At the time, investigators were complaining that they weren’t able to get adequate wavefront measurements on highly aberrated eyes,” Dr. Reinstein said. “Given that wavefront held the promise to help us correct complications, this was a concern. Therefore, one of the outcome measures of our study was to see if we could actually get readings through these disabled eyes and if those readings would be reproducible.”
All patients had severe complaints of visual disturbances ranging from night vision disturbances (starbursts, halo, glare and ghosting) to focusing strain and multiple images. The cases were so complex that one female patient with a decentered LTK treatment had seven images in her eye.
“Our primary aim in this study was just to get rid of the severe visual distortions. Who cares about the refractive error when you have seven images in one of your eyes?” Dr. Reinstein said.
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As is the case with many of these patients, he said despite the visual disturbances, 100% had 20/25 or better BCVA before enhancement surgery, and 60% were able to see 20/15 with correction. UCVA was 20/40 in 87% of patients and 20/20 in 40% of patients.
“In this pilot study, we set out to determine if the WASCA could even measure highly aberrated eyes, and if so, whether this could be done reproducibly, and if so, whether these measurements could reduce severe visual disturbances,” Dr. Reinstein said.
Enhancement treatment
Preoperative testing with the WASCA aberrometer was performed in the “dynamic mode,” which acquires up to 210 wavefront measurements in 30 seconds.
“Comparing multiple measurements of the same eye, the reproducibility was impressive,” he noted. “We found that with the WASCA aberrometer, which possesses the highest resolution available, we were able to attain reproducible measurements from even the most debilitated eyes, including two corneas that had undergone corneal transplantation and LASIK.”
“The highest reliability of the WASCA stems from its very high resolution sensor, with four times the number of lenslets compared to the next two closest units available,” he explained.
The researchers used this wavefront information to treat patients. “We divided the wavefront into the lower-order and higher-order aberrations,” Dr. Reinstein said. “We did this because we assumed that the lower-order aberrations could be corrected by ordinary lasers and treatment profiles. Here, we were interested in correcting the higher-order aberrations and the resulting visual disturbances.”
For the treatment, researchers applied higher-order aberration “profile reversals” onto the patients’ corneas using the MEL 70 G-Scan laser. Three months after surgery, aberrations were measured again and compared to preoperative measurements.
Improved quality, BCVA
Outcome measures were based on subjective improvement of symptoms, BCVA and changes in Zernike polynomial amplitude. Improvement in UCVA was not a primary outcome measure, but a factor that researchers considered a “bonus,” as they were not including refractive error data (lower-order aberrations) into the ablation profile.
Patients were asked to grade the change in their visual disturbances at the 3-month follow-up mark.
“We asked patients, if their visual disturbance was a ‘10’ in severity preoperatively, at what severity would they rank it now, on a scale of 1 to 10? If they answered a ‘2,’ then we knew that we corrected 8 out of 10, or 80%,” he said. Using this question, researchers found that 80% of the eyes had at least 70% improvement after enhancement surgery.
“So on the subjective scale, we were very successful in helping these severely handicapped patients,” he noted.
BCVA data showed that nine eyes that were 20/15 best corrected before surgery remained 20/15 best corrected after surgery. Three eyes that were 20/20 best corrected also remained 20/20 best corrected, but the three eyes that were 20/25 preoperatively all improved to a BCVA of 20/15 after surgery.
“This underlies the fact that many of the patients with debilitating vision after LASIK can have good Snellen visual acuities. Having said that, in this study, all eyes that fell below the 20/20 BCVA mark preoperatively were rehabilitated to a BCVA of 20/20 or better after surgery, in addition to having improved their symptoms,” Dr. Reinstein noted.
WASCA: Zernike high-order reproducibilityFrom 30 independent measurements of the same eye. Reproducibility (SD) <> Source: Reinstein DZ. |
Improved UCVA, wavefront
UCVA was also improved. “Many of the eyes already possessing 20/25 or 20/20 without correction had multiple images or other visual disturbances. By removing the multiple images, or improving their contrast, their uncorrected vision improved,” he noted.
In fact, 73% of patients had 20/15 UCVA 3 months after surgery, up from 20% preoperatively.
The researchers also noted an improvement in Zernike coefficients from the postoperative wavefront profiles.
“We had a 90% reduction in trefoil third-order aberrations, which was statistically significant (P = .001), and a 50% reduction in the total aberrations of the eyes (P = .013),” Dr. Reinstein said. The improvement of total aberrations occurred through the targeting of higher-order aberrations exclusively, he noted.
“The change in total aberrations equals the success rate of reducing the higher-order aberrations as a whole,” Dr. Reinstein explained. “This should be distinguished from studies that report an improvement in RMS total aberrations in which both higher- and lower-order aberrations (ie, the whole wavefront) are applied to the eye. In this case, the total RMS does not represent the improvement solely due to the correction of the higher-order aberrations, as a large proportion of the improvement can be attributed to the sphere and cylinder contained in the treatment.”
For Your Information:
- Dan Z. Reinstein, MD, MA (Cantab), FRCSC, can be reached at London Vision Clinic, 8 Devonshire Place, London W1G 6HP, UK; (44) 20-7724-1005; fax: (44) 20-7681-1233. Dr. Reinstein is a paid consultant for Carl Zeiss Meditec.
- Carl Zeiss Meditec, maker of the WASCA Aberrometer and MEL 70 and MEL 80 Excimer Laser systems, can be reached at 5160 Hacienda Drive, Dublin, CA 94568; (925) 557-4100; fax: (925) 557-4101.