Novel ablation profile shows promise for myopic LASIK

January 1, 2011

An ongoing European multicentre study is investigating a 'ray-tracing' ablation profile for myopic LASIK using an excimer laser. Results from patients treated by one investigator suggest superior outcomes relative to currently available ablation techniques.

Astudy evaluating outcomes in eyes undergoing LASIK for >-4 D of myopia reaffirms the established efficacy, safety and predictability of treatments performed with the wavefront-optimized (WFO), wavefront-guided (WFG) and topography-guided (T-CAT) ablation profiles of an excimer laser (WaveLight, Alcon Laboratories), and shows interesting promise for further improvement using an investigational 'ray-tracing' (RT) technique, reported Dr Arthur B. Cummings, at the annual meeting of the European Society of Cataract and Refractive Surgeons.

To match the RT study criteria, eyes were retrospectively identified that had been treated for >-4 D of myopia or >-2 D of astigmatism with a spherical equivalent (SE) of >-4 D. Considering eyes with follow-up to at least 3 months, there were 2659 eyes that underwent a WFO treatment, 25 that had T-CAT LASIK, 31 treated with a WFG approach and 57 eyes in the RT study group. Mean SE was highest in the WFO eyes (-6.32 ± 1.74 D) followed by the RT group (-6.08 ± 1.38 D), whereas mean SE was about -5.1 D in both the WFG and T-CAT cohorts.

Developed at the Institute for Refractive and Ophthalmologic Surgery, Zurich, Switzerland, the RT profile integrates data derived from topography, wavefront aberrometry and optical biometry, and performs the final calculations on a virtual model of the patient's eye rather than on the generic Gullstrand model.

The Allegretto WFG treatments were performed using data obtained with a Tscherning aberrometer and the T-CAT treatments used data from either Placido-disc (Topolyzer, WaveLight) or Scheimpflug (Oculyzer, WaveLight) technology. Both the 200-Hz (WaveLight Allegretto) and 400-Hz (WaveLight Allegretto Eye-Q) lasers were used for the treatments although the RT treatments were all performed on the 400-Hz laser.

UCVA at 3 months

Data on UCVA outcomes at 3 months showed about 82% of eyes treated with the RT technique achieved 20/20 or better, which surpassed the rates achieved in the WFO (64%) and T-CAT (58%) groups. All of the WFG eyes achieved 20/20 or better UCVA.

"I perform WFO ablation in the vast majority of patients that present for myopic LASIK of more than -4 D because findings from the FDA study indicated the WFG profile had a benefit only in eyes with higher wavefront error (>0.40 µm higherorder RMS). It was interesting to see there were better results using the WFG technique compared with WFO in this group, although the data need to be interpreted carefully considering the small number of eyes treated by a WFG approach," he emphasized.

"The fact that the T-CAT patients did least well was somewhat surprising because my experience with that protocol has been very positive, although in practice, its major role is as an enhancement technique in complicated, nontreatment-naïve eyes," Dr Cummings affirmed.

Safety outcomes in the three other groups far exceeded the FDA safety criteria that require a <5% rate for loss of 2 or more lines of BCVA. However, 10% of eyes treated with the WFG technique, 9% of eyes in the WFO group and 20% of T-CAT eyes had a 1-line loss of BCVA. Some eyes in each of these groups, albeit a very small percentage, lost 2 or more lines, he said.

Predictability analyses showed about 85% of eyes in all four groups were within 0.5 D of target refraction. Residual astigmatism calculated by vectoral analysis showed the best outcome in the RT group (0.20 ± 0.27 D).

Special contributor Dr Arthur B. Cummings is a consultant ophthalmologist at the Wellington Eye Clinic in Dublin, Ireland. He is an investigator for Alcon/WaveLight and can be reached by E-mail: abc@wellingtoneyeclinic.com