Refractive surgery has enjoyed unprecedented growth; it is the fastest growing of all human surgeries. PRK—the first universally popular refractive procedure—safely and successfully treats low-to-moderate myopia. Postoperative pain, regression, delayed visual recovery, and corneal haze, however, were significant issues. Improved surgical techniques resulted in the development of LASIK, which quickly became the procedure of choice. It provided painless rapid visual recovery and was relatively complication-free. Over time, however, complications (eg, incomplete flaps, buttonholes, quality vision issues, and lack of long-term data) have tempered our enthusiasm.
So, what has rejuvenated our interest in PRK and changed it from a procedure performed in less than 5% of patients to one currently performed in approximately 30% in many clinics? A modification of PRK known as LASEK appears to be the principal factor.
As a hybrid of PRK and LASIK, LASEK incorporates the advantages and minimizes the disadvantages of both procedures. In LASEK, a dilute solution of alcohol is applied to the cornea for a short time to loosen the corneal epithelium and create an epithelial flap. Following laser ablation, this flap is carefully replaced and repositioned on the cornea.
BIOMECHANICAL, CHEMICAL FACTORS
Impaired vision and less haze formation following LASEK compared with PRK have been attributed to biochemical and mechanical factors. It has been postulated that cytokines that are secreted by a regenerating epithelium activate the transformation of keratocytes to myofibroblasts. This transformation stimulates the healing process that, ultimately, results in corneal haze formation and regression. In LASEK, replacement of the epithelial layer onto the ablated cornea reduces this healing response and provides a mechanical barrier between the tear film and the stroma. This, however, is not the whole picture. Many epithelial cells die, even if dilute alcohol solutions are used, and thus do not provide a viable mechanical barrier. Second, during procedures where the epithelial flap is lost, inadvertent PRK findings of less haze and rapid visual recovery comparable with LASEK occur, which are much less than previously explained with PRK. Therefore, additional undetermined factors must also play a major role.
STUDIES
Several studies examine the refractive and visual topographical outcomes in patients following LASIK in one eye and LASEK in the fellow eye. Each concluded that there was no difference in parameters for both treated groups during the postoperative follow-up of 1 year. Beyoglu et al1 found a postoperative decrease in contrast sensitivity in LASIK-treated eyes but it was not detected in fellow LASEK-treated eyes. In a retrospective, nonrandomized, case-controlled study of 2,251 eyes treated for up to 6.00 D of myopia with LASIK or LASEK, Tobaigy et al2 found visual and refractive outcomes to be marginally superior in LASEK-treated eyes. Scerrati et al3 found LASEK results were superior to LASIK at 6-months follow-up in 15 LASIK and 15 LASEK eyes. Other studies also supported the findings that LASIK results are not superior to those of LASEK.4,5
Long-term outcome is one of the most frequently asked questions by patients contemplating laser surgery. Recent studies showed that stability, safety, and a high degree of patient satisfaction in patients treated for low-to-moderate myopia by PRK at 12-year follow-up.6 No comparable long-term follow-up studies concerning LASIK have yet been published in the literature.
INDICATIONS
Although LASIK has been the procedure of choice, PRK is indicated in patients with a corneal thickness of less than 500 µm and particularly in patients who have moderate myopia. Other indications include recurrent corneal erosion, patients with anterior basement membrane dystrophies or narrow palpebral apertures, and nervous patients. Revised indications include postpenetrating keratoplasty and postattempted LASIK, where incomplete flaps or buttonholes have occurred. It is also the procedure of choice in patients who have regression or myopic shift several years after LASIK, or where a flap lift or a repeat cut is either unsafe or not an option. Patients who play certain contact sports or those in occupations such as the military may also be better suited for LASEK. (See Indications for LASEK).
The current approach to LASIK (ie, cutting a thin flap of 110 µm or less) may result in difficulty relifting the flap when regression treatment is needed in the future. Furthermore, performing surface ablation on these thin flaps may also increase the risk of buttonhole formation. Therefore, LASEK may be the procedure of choice for many patients—particularly those aged in their 20s—because retreatment may be necessary for regression or myopic shift.
Economic issues are also relevant. Refractive surgery has changed the dynamic in many countries, so that commercial and not medical personnel dictate clinical practice. The advent of cut-price competition has led to the reduction of professional fees. Added to the availability of more expensive technology (eg, femtosecond laser), the cost of surgery has increased. Therefore, LASEK negates the need for expensive keratomes.
A recent refinement of LASEK, in which the epithelium is mechanically separated from the stroma (ie, Epi-LASIK), will potentially add significantly to the cost of surface laser ablation. O'Doherty et al7 compared the clinical outcomes of PRK, LASEK, and Epi-LASIK. Epi-LASIK was associated with less pain, however, there was no difference in haze. The investigators reported a high failure with the keratome, whereas 33% of the Epi-LASIK procedures were converted to PRK. (For more information on Epi-LASIK, see page 26.)
USE WITH HIGH MYOPIA?
LASEK has now established itself as an excellent alternative to LASIK in low-to-moderate myopia, however, we still do not have useful data concerning treatment of high myopia. Many patients who had PRK for high myopia in the 1990s developed severe haze, which in some cases resulted in permanent corneal scarring. In patients treated for low-to-moderate myopia, haze faded over time. In a LASEK refinement, diluted mitomycin C is a successful prophylaxis for haze development as well as treatment of established haze. Studies using a concentration of 0.02% for as few as 12 seconds have shown no adverse effects on the cornea, either short- or long-term.8 Many refinements that have improved quality vision in LASIK (eg, larger optical zones and wavefront technology) are now being used in LASEK. It would be unwise to write off LASIK, however, as it still remains a magical procedure for many patients.
What is changing the dynamic is the fear of long-term complications, the lack of versatility and long-term data, and cost. Safety, economics, and excellent longer-term visual results have rejuvenated LASEK, and it is now a serious competitor of LASIK. The single biggest obstacle to its further advancement is the lack of any adequate method to eliminating postoperative pain.
Michael O'Keefe, FRCS, practices in the Department of Refractive Surgery, Mater Private Hospital, in Dublin, Ireland. Professor O'Keefe states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +00 353 1 8858626; fax: +00 353 1 8858490; or mokeefe@materprivate.ie.
Caitriona Kirwan, MRCOphth, practices in the Department of Refractive Surgery, Mater Private Hospital, in Dublin, Ireland. Ms. Kirwan states that she has no financial interest in the products or companies mentioned. She may be reached at tel: +00 353 1 8858626; fax: +00 353 1 8858490.
Up Front | Mar 2007
The Case for LASEK
This surface ablation technique is now a vicious competitor of LASIK.
Michael O'Keefe, FRCS, and Caitriona Kirwan, MRCOphth
