Dermot McGrathin Lisbon

WAVEFRONT-guided LASIKperformed with the IntraLasefemtosecond laser offers slightlybetter clinical results, faster visualrecovery and an improvement inlow light contrast acuity comparedto procedures performed withmechanical keratomes, accordingto David Tanzer MD.

Presenting the results of aprospective, parallel groupcomparison trial, Dr Tanzer saidthe goal of the study was tocompare the performance of thefemtosecond laser to mechanicalkeratomes in terms of flapcharacteristics, refractive and visualoutcome, quality of vision andwavefront aberrations.

He set out to evaluate the besttechnology for the creation of aLASIK flap in preparation forstudying the efficacy of LASIKsurgery in Naval aviators.At themoment, PRK is the onlytreatment we use for aviators, saidDr Tanzer, Surgical Director,Refractive Surgery Center,Department of Ophthalmology,Naval Medical Center, San Diego.

Dr Tanzer and colleagueSteven Schallhorn MDperformed all surgeries with theAMO/VISX Star S4CustomVue™ platform usingthe Zernike-based softwareupgrade.The study included 600eyes of 300 patients whounderwent LASIK flap creationwith the femtosecond laser(IntraLase), the Amadeusmicrokeratome (AMO), or theHansatome (Bausch & Lomb)microkeratome. Dr Tanzernoted that all groups wereclosely matched in terms of ageand refractive sphericalequivalents.

Staged and unstagedproceduresHalf of the patients in eachkeratome group receivedwavefront-guided LASIK in thestandard fashion with the flapscreated and lifted, followed byimmediate application ofwavefront-guided excimerablation.The other half of thepatients underwent a stagedprocedure, where the flaps werecut, lifted and immediately laidback into position.Thesepatients had wavefrontmeasurements obtained at theone-month post-operativeexamination and, based on thatmeasurement, the flaps werelifted and the ablation wasperformed.

The idea of the staged approachwas to take into account anyaberrations induced by thecreation of the flap, said Dr Tanzer.

Measurements were completedpreoperatively and one day, oneweek, one and three monthspostoperatively. Flap thicknessvariance was greater formechanical keratomes than thefemtosecond laser keratome.Patients had more symptoms suchas foreign body sensation andphotophobia on day one in the

femtosecond laser group(p<0.001), but these differenceswere nullified after one week,reported Dr Tanzer.

Faster visual recovery withfemtosecond Uncorrected visual acuity wasbetter in the femtosecond group atone day, one week and one monthpostoperatively (p<0.001), but notsignificantly different frommechanical keratomes at thethree-month follow-up visit.

The clinical visual acuity resultsat one day, one week and onemonth favoured the IntraLase,although there was no statisticaldifference between the threekeratomes by three months.However, gain in mesopic 25%contrast acuity at three monthspost op compared to preop wassignificantly better in thefemtosecond group (+0.03 logMARloss for Amadeus, -0.01 logMARgain for Hansatome and -0.04logMAR gain for IntraLase).

The best-corrected acuityresults at three months showed nolosses of more than one line in anygroup. However, 45% of IntraLaseeyes compared with only 33% of

eyes in either mechanicalmicrokeratome group experienceda gain of one line.

Dr Tanzer noted that analysis ofhigher order aberration (HOA)induction solely by the creation ofthe flap indicates that the IntraLaseinduces less HOA than either theHansatome or the Amadeus.TheIntraLase resulted in neither a gainnor loss of HOA at one monthcompared to induction of HOA forthe Amadeus and Hansatome(+0.03 microns for both).

While there were no statisticallysignificant differences in overallRMS values, the study found thatthe Amadeus keratome inducedmore spherical aberration, andboth the Amadeus and theHansatome induced morehorizontal coma compared toIntraLase, said Dr Tanzer.

He added that a comparativeanalysis between the consecutiveand staged approach indicated nosignificant improvement in clinicaloutcomes by taking into accountaberrations induced by thecreation of the flap.

Dr Tanzer said that while theresearchers had originallyhypothesised that a staged

approach taking into account theaberrations induced by creation ofthe flap might result in better visualoutcomes, the clinical results thusfar suggests no discernibledifference between the twoapproaches.

He concluded that there werebeneficial effects to using thefemtosecond keratome, in terms ofclinical results, faster visualrecovery and improved mesopiccontrast acuity. The stagedapproach to LASIK offered noclinical advantages over thetraditional approach, regardless ofthe keratome used. Finally, therewere no significant differences inoverall HOA induced by anykeratome, but the Amadeusinduced more spherical aberrationand both mechanical keratomesinduced more horizontal comathan the femtosecond keratome.Based on the results of this study,further studies will be conductedto evaluate the safety and efficacyof LASIK in Naval aviators.

David J Tanzer MDdjtanzer@nmcsd.med.navy.mil

Study suggests femtosecond laser offers advantages overmechanical keratomes in wavefront-guided ablations

EuroTimes December 2005

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David Tanzer