Wavefront-guided LASEK offers little benefit over standard algorithm in normal eyes

From ESCRS Euro Times Feb 2004: (reporter Daithi O hAnluain in Chester, UK)

A prospective study presented at the annual meeting of the United Kingdom and Ireland Society of Cataract and Refractive Surgery (ESCRS) found that corneal wavefront guided LASEK offered no benefit over standard algorithms for myopia and compound myopic astigmatism in eyes without large amount of higher-order aberrations.

The randomised study included 22 patients (44 eyes) who underwent bilateral LASEK for myopia and compound myopic astigmatism. The mean age of these patients was 35 years (range 22-59 years). The mean preoperative spherical equivalent was -5.06 D (range -1.375 to -9.75 D). The mean preoperative  cylindrical error was -0.8 D (range 0 to -2.5 D). One eye of each patient was treated using the standard algorithm and the other was treated using a corneal wavefront-guided ablation with the Schwind ERISIS laser.

"This system has been extremely useful in treating highly aberrated eyes such as those after corneal grafting procedures and following previous corneal and refractive surgical procedures. The aim of this study was to see if it could offer any significant advantages over the standard ERISIS algorithm, which only corrects lower order aberrations" reported David P.S.O'Brart MD.

All 44 eyes were treated with a LASEK technique using a 15% alcohol application for 20 seconds. The full scotopic pupil diameter was treated in every case and optical zone sizes between 6.5 and 7.5 mm were used in this study. Identical optical zones were used in both eyes of each patient.

Preoperatively there were no differences between the two groups in terms of uncorrected visual acuity (UCVA) and best corrected spectacle visual acuity (BCSVA), spherical and cylindrical refractive errors and root mean square (RMS) values for higher order aberrations. The mean RMS value (Higher order only) was 0.61 microns (range 0.45 microns to 0.86 microns).

"Postoperatively there were no differences in refractive outcomes, with both groups achieving very satisfactory results." said David O'Brart.

All eyes treated with corneal wavefront-guided ablation were within one dioptre of emmetropia at the six month follow-up visit, with 81% within half a dioptre of the intended correction. Similarly, all of those treated with the standard algorithm were within one dioptre of the intended correction, and 89% were within half a dioptre.

The study revealed no difference in refractive outcome in terms of spherical or cylindrical treatments between the two treatment groups. Visual recovery, corneal haze, and post-operative visual acuity were similar in both groups.

"Interestingly, there were no differences in the higher-order aberrations either in terms of overall RMS values or more specifically trefoil, coma or spherical aberration" said David O' Brart.

RMS values increased significantly in both groups (p<0.005) and this was mainly because of an increase in 4th order spherical aberration with both the standard algorithm treatment and the corneal wavefront treatment (p<0.005). Despite the increase in 4th order spherical aberration, no patients reported any problems with either mesopic or scotopic vision.

"Excellent outcomes were achieved using the Schwind ERISIS laser with both its standard algorithm and corneal wavefront treatments. There was no benefit over the standard algorithm using corneal wavefront treatment in terms of inducing or preventing higher order aberrations post operatively" said Dr O'Brart.

He commented that it was interesting that 4th order spherical aberration increased in both groups despite full treatment of the scotopic pupil diameter in every case. As this is the main component of the increase in overall RMS values for higher-order aberrations postoperatively, further strategies need to be developed to both reduce and prevent 4th order aberrations following corneal laser refractive surgery.

He noted that studies in the published literature ( Nuijts RM,  J. Cat. Ref Surg 2002; 28: 1907-13 and Phusitphoykai N, J Cat Ref Surg  2003; 19:S2 17-20 ) confirm the results of his study. Both were randomised,, bilateral, controlled studies comparing wavefront treatments in one aye and standard treatments in the other.

These two studies used LASIK and the wavefront-guided wavefront-guided treatments of the Nidek NAVEX system in one study and the Zyoptix, Bausch and Lomb in the other. Both studies concluded that there was little difference in terms of postoperative visual performance and refractive outcomes between standard algorithms or wavefront guided ablations.

"That is not to say that wavefront treatments do not have a role in refractive surgery. In the treatment of highly aberrated eyes e.g. after penetrating keratoplasty or previous refractive surgery, wavefront treatments can be extremely useful. We have a cohort of over 30 eyes with severe high order aberrations, where the results of corneal wavefront LASEK treatments have been very encouraging indeed. However, in eyes without pre-existing high order aberrations it appears to have a very limited role" he told Euro TImes.

David O'Brart MD, FRCOphth

St Thomas' Hospital, London