Epi-LASIK is a comparatively new procedure in corrective vision surgery which draws on an older technique of removing the thin layer of surface cells covering the cornea before, in turn, removing microscopic amounts of corneal tissue.

Using a laser to change the curvature of the cornea, the eye surgeon can create a lasting refractive effect for the patient. By altering the pattern created on the cornea, shortsightedness, longsightedness or astigmatism can be corrected.

With this basic understanding of the surface-based procedure, the name now becomes clearer: "Epi ? stand for epithelial which are the surface cells covering the cornea; LASIK stands for laser-assisted in situ keratomileusis which describes the process of using a laser to reshape (mileusis) the cornea (kerato) from within (in situ).

Epi-LASIK stands in contrast to LASIK surgery where the epithelial cells are not removed. Here a thin flap of corneal tissue (approximately 25% of the corneal thickness) is created complete with the overlying epithelium. The hinged corneal flap is then lifted to one side, the deeper cornea treated with the laser and the flap reseated.

Why this resurgence in surface-based corrective vision surgery? What advantages does Epi-LASIK have over older surface ablation techniques such as PRK or the more recent LASEK surgery, and the "flap and zap ? procedures like LASIK? Let's make some comparisons:

Epi-LASIK evolved as a result of drawbacks and complications in the traditional PRK and newer LASEK surface-based procedures, as well as the more radical, flap-creating LASIK technique.

In PRK, the epithelium is rubbed away before the laser is fired into the cornea to reshape its curvature. In effect, a large abrasion is created by removing the epithelial cells, and this wound often means much discomfort for the patient.

In addition, all patients develop at least a mild degree of haze in the central cornea which can compromise vision and create haloes around lights. Although, in the majority of cases, this disappears within 6 months, corneal haze continues to be an issue limiting the range of safe refractive change with PRK.

LASEK differs from PRK primarily in its use of alcohol to release the epithelium which then serves as a biological bandage-cum-contact lens.

Patient comfort and the problem of corneal haze improved as a result of using the new technique. However, the alcohol solution was found to delay visual recovery. It also created an unstable epithelial layer until the cells were replaced, killing all the epithelial cells with which it came into contact.

LASIK, as we have seen, involves the creation of a hinged corneal flap. A virtually painless procedure allowing a greater range of refractive correction, it nevertheless still presents problems associated with the flap itself and the optical complications arising from the flap's creation.

Epi-LASIK attempts to provide the best of both worlds, combining the distinct advantage of surface-based procedures (no flap) with the particular advantages of LASIK (less pain and a quicker recovery time).

The crucial differences with Epi-LASIK, and the enormous benefits these offer in terms of shortened visual recovery time and reduced risk of complications, centre on the method used to lift the epithelium off in a single sheet and the absence of alcohol.

LASEK, too, involves cutting the epithelium in a thin sheet, but in Epi-LASIK a blunt blade is used instead of a sharp surgical tool. Similarly, a plastic blade is used to separate the epithelial sheet from the eye in Epi-LASIK and no alcohol is used. The damage to the eye is, therefore, kept to a minimum while the repositioned epithelium, acting as a bandage, promotes even faster healing.

Recent studies have demonstrated very promising results for Epi-LASIK. In one study Epi-LASIK surgery was used to retrieve an amputated flap following a complicated primary LASIK procedure. The uneven corneal contour at the site of the original hinge did not preclude a successful outcome, and there is optimism that other flap-related complications can be managed by the Epi-LASIK procedure in the future.

In another longitudinal study one-year outcomes of Epi-LASIK surgery for myopia were evaluated. The results were very encouraging with the report's authors concluding that this procedure is both safe and efficient. Patients displayed only mild discomfort, mild temporary corneal haze and no loss of any lines of best spectacle-corrected visual acuity (BSCVA), with 1 in 6 actually gaining one or two lines of BSCVA.

However, post-operative contrast sensitivity proved a more persistent problem for patients with moderate to severe myopia. This finding supports the generally-held view that Epi-LASIK is more suitable for people with less steep corneas who have less severe myopia.

Other likely candidates also include those with thin corneas - LASIK requires more corneal tissue in order to create a satisfactory flap - and those people who run the risk of having their flap dislodged. Police officers and tennis players, for instance, who stand an increased chance of being hit in the face, would be better advised to have Epi-LASIK rather than conventional LASIK.

As this technique is a relatively new version of surface-based corrective vision surgery, make sure that you discuss your prospective surgeon's success rates with this procedure. Several post-operative visits are required to check corneal healing and visual acuity, so make sure that the type of care provided includes all such associated costs.