ADVANCES IN LASER TECHNOLOGIES

Advances in femtosecond and excimer laser technologies are continuing to yield vastly improved results for astigmatic correction in both myopic and hyperopic patients, according to a French study presented at the French Implant and Refractive Surgery Association (SAFIR) annual meeting. “Thanks to improvements in femtosecond and more particularly excimer laser technology we are now seeing very good visual and refractive outcomes for both sphere and cylinder that remain stable over time,†Philippe Chastang MD told delegates.

Dr Chastang, Cabinet d'Ophtalmologie La Motte-Picquet and Fondation Ophtalmologique Rothschild, Paris, France, noted that LASIK has been the technique of choice in recent years to correct astigmatism up to around 6.0 D. “Hyperopic treatments seem to have benefited the most compared to what was possible five years ago. And while the astigmatic results overall are still not quite as good as for purely spherical treatments, the gap is closing all the time,†he added.

The introduction of the femtosecond laser has enabled refractive surgeons to adjust the flap cut to the geometry of the photoablation and deliver greater control over the placement of the hinge and the shape of the cut, Dr Chastang said. The biggest breakthrough, however, has been in the domain of excimer laser technology. “We now have flying spot lasers, with advanced eye tracking capability, ablation profiles with larger optical treatment zones and improved correction of cyclotorsion,†he said. The issue of cyclotorsion is one which has caused problems for refractive surgeons over many years, said Dr Chastang. “We know the effect of axis alignment errors on LASIK treatments. An error of seven degrees equates to a 25 per cent reduction in the efficacy of the laser treatment, 15 degrees equates to 50 per cent and 30 degrees means the effect has been completely nullified,†he said. In order to assess the progress made in astigmatic corrections in recent years, Dr Chastang carried out a retrospective study of 71 eyes with a cylinder greater than 2.0 D treated over a three-year period. The study included 44 myopic eyes with astigmatism from 2.0 D to 4.75 D and 27 hyperopic eyes with astigmatism from 2.0 D to 5.0 D. The IntraLase femtosecond laser (Abbott Medical Optics) was used to create 100 to 110 micron flaps with diameters ranging from 8.8 to 9.3mm. Photoablation was carried out using the Wavelight Allegretto 400 Hz laser (Alcon Laboratories), which incorporates sophisticated eye-tracking capabilities, said Dr Chastang.

Eye tracker

He noted that the WaveLight laser uses an advanced eye tracker that recognises any eye movement and actively tracks pupillary diameters from 1.5 to 8.0mm. The NeuroTrack feature prevents cyclorotation by giving the patient a target to look at that incorporates square elements and prevents the eye from rotating. A projected crosshair line over the patient’s eye informs the surgeon of the exact alignment of the patient’s head and eye, while the tracker uses the vestibulo-ocular reflex to track all eye movements actively and compensate for the cyclotorsion. Dr Chastang said that 82 per cent of patients with myopic astigmatism and 85 per cent of those with hyperopic astigmatism achieved between -0.5 D and +0.5 D residual spherical equivalent after six months. The postoperative subjective cylinder showed 77 per cent of myopic patients and 85 per cent of hyperopic patients had less than 0.50 D of cylinder. “What we can see is that the hyperopic results have improved considerably on previous generations of laser technology and are now relatively comparable to myopic cylinder corrections,†he said. Dr Chastang has no financial interest in the products mentioned in this article.