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in Munich A NEW technique combining LASIK and LASEK characteristics may create a healthier epithelial flap, improve postoperative healing and reduce the risk of haze, according to its developer Ioannis Pallikaris MD. The technique involves the mechanical separation of the epithelium from the Bowman's membrane with a specially designed epithelial separator device. Since it does not involve the use of alcohol it has no toxic effects on the epithelium, said Dr Pallikaris, who will be presenting his findings here at the XXI Congress of the ESCRS. Dr Pallikaris and his associates carried out a study involving 10 eyes of 10 patients who underwent de-epithelialisation either through alcohol-assisted LASEK or with the new customised epithelial microkeratome. Microscopic examination of the removed epithelial sheets showed a smooth and undisrupted basementl membrane in those created mechanically, while in those created with alcohol the basement membrane had significant disruptions, he noted. "We found that mechanical separation of the epithelium preserved epithelium stratification and integrity with minimal trauma and oedema," Dr Pallikaris said. In the six eyes which underwent mechanical epithelial sheet creation, the sub-epithelial separator cleaved the epithelium at the level where lamina densa of the basement membrane makes contact with the Bowman's membrane. Moreover, the lamina densa and lamina lucida of the mechanically separated epithelial sheets all had normal morphology along nearly the whole length of the basement membrane. In contrast, in the four eyes which underwent alcohol-assisted flap creation, the cleavage plane was within the basement membrane. Furthermore, the lamina lucida layer of cells demonstrated significant interruptions, while lamina densa cells were almost entirely absent. The concentration of alcohol used in the conventional LASEK group was 15% or 20%. The solution was left on the eye for 20 seconds, he noted. In eyes which underwent mechanical flap creation, Dr Pallikaris used a suction ring and then applied his specially customised epithelial separator to the epithelium. "It looks like a LASIK microkeratome but it isn't. It has a dull plastic blade which doesn't cut through the cornea but only separates the epithelium from the Bowman's membrane. It is then easy to fold the flap back using a merocel sponge," he said. Dr Pallikaris noted that LASEK was introduced a few years ago as a means of correcting refractive errors with the comfort and rapid rehabilitation of LASIK and the safety of PRK. Early reports indicated that patients undergoing LASEK did appear to experience less pain than they would with PRK, although still slightly more than LASIK. They also had a more rapid normalisation of their epithelial tissues with less postoperative haze. The advent of customised ablation has brought about a resurgence of interest in PRK, as refractive surgeons became aware that the creation of LASIK flaps induces aberrations in an unpredictable way. Several reports, notably those of Marguerite MacDonald MD and from Dr Pallikaris' own centre supported the theory that customised surface ablations produced more predictable results than customised LASIK. Subsequent studies have indicated that LASEK has several of the same advantages as PRK, and that just as with conventional non-customised ablations it achieves the advantages with less pain and less haze. However, some centres have reported more equivocal results with some cases of delayed healing and haze. These effects are more pronounced when higher concentrations of alcohol are used, Dr Pallikaris said. "The major problem with LASEK is related to alcohol. It has been histologically proven that alcohol has an effect on the basal epithelial membrane and generally 80% of cells in a LASEK epithelial flap will die within the first postoperative day. Furthermore, when we use alcohol we separate the membrane between the two layers of the basal membrane, the lamina densa and the lamina lucida, undermining the integrity of the separated epithelial sheet. "With Epi-LASIK however, the basal membrane remains intact and the epithelial cells are able to generate hemidesmosomes which can serve to anchor the flap to the stroma. Furthermore, the intact double lamina can act as a shielding mechanism and prevent the activation of keratocytes. With LASEK and PRK the activation of the exposed keratocytes induces the production of disoriented collagen fibres, which is the origin of haze." Dr Pallikaris said he and his associates have so far used the epi-LASIK technique in 30 eyes in 30 patients. All of the patients underwent PRK in their fellow eye and nearly all cases have had a follow-up of three months and some have had six months follow-up. He noted that while it is still too early in the study and the groups were too small to quantitatively compare haze outcomes, all of the epi-LASIK eyes so far appear to have almost no haze while the PRK do appear to have noticeable amounts in some cases. As a further enhancement to the technique, Dr Pallikaris has begun using dehydrated contact lenses to lift the epithelium. After performing the laser ablation he uses the contact lens to flip the epithelial flap back in place. After a few days, when epithelial healing allows the flap to adhere to the stroma, he removes the lens. It is alternatively possible to remove the lens by rehydrating it, which automatically separates it from the flap without lifting the flap from the stroma, he said. Ciba Vision is planning to market the new microkeratome under the name Centurion SES™. Versions will be available for both LASIK and LASEK. Dr Pallikaris said he expects CE mark and FDA approval for the device within the next month. Ioannis Pallikaris MD Heraklion University Hospital, Crete, Greece pallikar@med.uoc.gr |
