Back to the Surface Refractive surgeons review …

1 Cheryl Guttmanin New OrleansALTHOUGH LASIK quickly rose tobecome the predominant method for laservision correction after it was introduced,various factors subsequently fuelled aresurgence of interest in Surface ablationtechniques, and these procedures haveregained popularity particularly amongEuropean Refractive a Refractive surgery subspecialtymeeting held during the annual meeting ofthe American Academy of Ophthalmology,leading ophthalmic surgeons debated thepros and cons of Surface C Knorz MD, professor ofophthalmology, University of Heidelberg,Germany undertook the task of discussingthe cons of Surface ablation. Nonetheless,he emphasised that it remains a great toolthat belongs in the Refractive surgeon'sarmamentarium. However, its use shouldbe limited to certain patients, said DrKnorz. Typical indications are patients withthin corneas, epithelial basal membranedystrophies, or asymmetric cornealtopography, he disadvantages of Surface ablationare underlined by comparing it to LASIK,as Surface ablation is associated with morepostoperative discomfort, a slower visualrecovery, and worse efficacy and safetyresults.

2 Any previous advantage of surfaceablation for minimising induced higherorder aberrations has also been eliminatedwith use of a femtosecond laser for flapcreation, said Dr cited a prospective study conductedby Daniel Durrie MD and Stephen SladeMD that compared wavefront-guided thin-flap LASIK (SBK with a femtosecond laser-created 100 micron, flap) andadvanced Surface ablation in fellow eyes of50 bilaterally operated study showed that at follow-upvisits through the first month aftersurgery, the advanced Surface ablationprocedure was associated with more painand lower patient were significantly better in theLASIK eyes on the first day after surgeryand remained so through at least threemonths. In contrast to expectations,changes in higher order aberrations frombaseline were similar in the two groups ofeyes at six Knorz also referred to a meta-analysis undertaken by Shortt et al. thatfound Surface ablation was associated withpoorer efficacy and safety outcomescompared with LASIK.

3 Published inOphthalmology in 2006, the meta-analysisincluded data from prospective,randomised controlled studies comparingLASIK and PRK for treatment of authors also reviewed prospectivedata from FDA case series of myopicLASIK and PRK and similarly concludedfrom those results that LASIK was a moreeffective and safer favour of Surface ablationDimitri T Azar MD discussed the pros ofsurface ablation. He emphasised its safetyadvantages. Compared with LASIK, surfaceablation avoids flap and microkeratome-related complications and minimises therisk of ectasia, said Dr Azar, professor andhead of the department of ophthalmology,University of Illinois, Chicago. Understandably, ectasia is more likelyto occur after LASIK because thatprocedure increases corneal weakeningand decreases its biomechanical ectasia can occur after surgeryin myopic patients, especially in eyes wherekeratoconus was not diagnosed pre-operatively, but there is also an increasedrisk after treatments involving thick flapsor deep ablations, he ablation can also be a viablealternative for treating higher levels ofmyopia if it is performed with mitomycin-C (MMC) for haze prophylaxis, and it maybe a better alternative to phakic IOLimplantation in certain situations.

4 Inparticular, Surface ablation might beconsidered for patients with shallowanterior chambers, low endothelial cellcounts, a history of progressive endothelialcell loss, early cataracts, or highastigmatism, Dr Azar said. Over the next years, surgeons canexpect to see continued evolution in theindications and boundaries for surfaceablation, Dr Azar best if both worlds?John Marshall MD, professor ofophthalmology, Kings College, London, UK,reviewed the research that explains theproblems of pain and haze after surfaceablation procedures, the adverse effects ofLASIK on corneal biodynamics, and therationale for SBK. He explained that hazeafter PRK is the result of interactionsbetween cytokines released simultaneouslyfrom surgically injured epithelial cells andstromal keratocytes. While the newersurface ablation techniques of LASEK andepic-LASIK showed some benefit forcontrolling haze, they failed to completelyeliminate it.

5 After LASEK and epi-LASIK, theepithelial cells still release cytokines, butthere is an uncoupling between thosemediators and the signals coming from thestromal keratocytes. Nevertheless, lifting ofthe epithelium in those Surface ablationprocedures leads to rupture of thehemidesmosomes on the basal border ofthe basal epithelial cells, no matter howmuch care surgeons take to leave the cellsintact. These are cells that have beendamaged and so will release cytokines thatlead to haze, Dr Marshall added that conceptually, LASEK could be a better procedure if theepithelial cells are killed when the flap islifted and then replaced so that the tissueserves purely as a biological avoiding epithelial damage, LASIK mitigated the postoperative problems ofhaze and pain associated with surfaceablation procedures. However, studiesfrom Dr Marshall and his colleagues raisedconcern about its effect on cornealbiomechanical stability.

6 Recognising thatthe traditional LASIK flap cut through thecornea in its weakest areas both in termsof depth and eccentricity, studies wereundertaken using sophisticatedmeasurement techniques to investigate theeffects of various flap features on from that research indicatedbenefits of thinner, narrower, and planarflaps. With the opportunity for reliablecreation of such flaps using thefemtosecond laser, the idea of SBK from the study from DrsDurrie and Slade along with otheremerging data are suggesting that SBK mayfulfil its promise of providing thebiomechanical stability of PRK without itspain and haze. Larger and longer-termexperience is needed to better define theefficacy and safety profile of SBK,according to Dr Marshall suggested thatbiomechanical stability after SBK might befurther increased by changing the edgeangle of the flap so that it is more ablation procedures may also befurther improved using a technique DrMarshall termed pharmacologicallymodulated PRK where novel modalitiesare used to control the wound healingprocess responsible for haze and told attendees that researchconducted to date indicates use of asimple sugar, mannose 6-phosphate, andaptamer technology represent twopossible strategies.

7 Mannose 6-phosphateblocks receptor sites on keratocytes andhas been shown to prevent haze in testingin animal models. The aptamers areengineered to selectively differentiatebetween activated and latent keratocytesin order to allow targeted wound surgeons review Surface ablationpros, cons, and alternate solutionsSpecial FocusMichael C KnorzBack to the Surface Typical indications arepatients with thin corneas,epithelial basal membranedystrophies, orasymmetric cornealtopography Michael C Knorz MD After LASEK and epi-LASIK, the epithelialcells still releasecytokines, but there is anuncoupling between thosemediators and the signalscoming from the stromalkeratocytes John Marshall MDIf you are an ophthalmologist,this is the podcast you shouldbe listening to will discuss the big issues incataract and Refractive surgerywith our panel of experts. And ifyou have any suggestions as towho should be on EuroTimesPodcasts, please let us know.