Epi-LASIK is an addition to the surgeons' refractive armamentarium. This technique blends principles employed in other refractive procedures. It achieves similar visual outcomes without causing patients significant discomfort or potential postoperative complications. Epi-LASIK combines the creation of a corneal flap (as with LASIK) and the surface ablation aspects of PRK through a special instrument that mechanically separates the epithelium and basement membrane from the underlying stroma.

The following articles were reviewed:

1. Pallikaris IG, Katsanevaki VJ, Panagopoulou SI. Laser in situ keratomileusis intraoperative complications using one type of microkeratome. Ophthalmology. 2002;109:57-63.
2. Pallikaris IG, Kymionis GD, Astryakakis NI. Corneal ectasia induced by laser in situ keratomileusis. J Cataract Refract Surg. 2001;27:1796-1802.
3. Pallikaris IG, Kalyvianaki MI, Katsanevaki VJ, Ginis HS. Epi-LASIK: preliminary clinical results of an alternative surface ablation procedure. J Cataract Refract Surg. 2005;31:879-885.
4. Lee JB, Seong GJ, Lee JH, et al. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg. 2001;27:565-570.
5. Shah S, Sebai Sarhan AR, Doyle SJ, et al. The epithelial flap for photorefractive keratectomy. Br J Ophthalmol. 2001;85:393-396.
6. Pallikaris IG, Naoumidi II, Kalyvianaki MI, Katsanevaki VJ. Epi-LASIK: comparative histological evaluation of mechanical and alcohol-assisted epithelial separation. J Cataract Refract Surg. 2003;29:1496-1501.
7. Netto MV, Mohan RR, Ambrósio Jr R, et al. Wound healing in the cornea: a review of refractive surgery complications and new prospects for therapy. Cornea. 2005;5:509-522.

THE BIRTH OF Epi-LASIK
The goal of refractive surgery remains unchanged — to provide patients with the best possible UCVA, the least amount of postoperative pain, the quickest recovery and the highest level of safety. PRK is a safe and predictable technique for the correction of myopia, hyperopia and astigmatism. The postoperative pain, the delayed visual recovery and the risk of postoperative haze associated with PRK, however, opened the doors for a newer procedure. LASIK employs patients' own tissue as a therapeutic contact lens. Because the surgeon creates a stromal flap and ablates the underlying corneal stroma, LASIK effectively addresses the problems that PRK previously presented. The downside to this procedure is that surgeons must address complications such as irregular flaps, flap striae, epithelial ingrowth, interface inflammation and infection.¹ Furthermore, ophthalmologists' fear of corneal ectasia placed a limitation on deep ablations.²

Introduced in 1999, LASEK combines the principles of PRK and LASIK.³ Surgeons apply a diluted alcohol solution that allows the removal of the corneal epithelial layer as a continuous sheet, and they also create an epithelial flap. After performing photoablation of the corneal surface, the epithelial sheet is replaced onto the corneal surface. This step is considered to have a beneficial effect on wound healing.^4,5 According to Pallikaris et al,6 the result of using 15% and 20% alcohol solutions to obtain epithelial disks results in the formation of cytoplasmic fragments of the basal epithelial cells, enlarged intercellular spaces and discontinuities of the basement membrane. If the epithelial sheet could be separated without the use of alcohol, the epithelial flap may remain viable and provide faster recovery and less haze.

The term epi-LASIK refers to a new approach in refractive surgery. Instead of a metal-bladed microkeratome, the surgeon uses an epikeratome with a blunt plastic blade. This blade mechanically separates a sheet of epithelium along the natural cleavage plane, above Bowman's layer and below the basement membrane. After completing photoablation, the surgeon places the sheet back onto the stromal surface. This process eliminates the use of a metal blade or alcohol, theoretically avoiding flap complications and alcohol-related changes at the cellular and basement membrane levels.

CORNEAL WOUND HEALING AND PAIN
Clinical outcomes in refractive procedures are largely dependent on the corneal healing response. When epithelial cells or the basement membrane is disrupted, cytokines are released. A cascade of inflammatory reactions is initiated that sends signals for myofibroblasts' proliferation.7 The end result of this biochemical activity may be haze and regression, especially in PRK when epithelial tissue is completely destroyed.

The basement membrane, which is assumed to provide stability and support to the epithelium, remains intact in epi-LASIK without the discontinuities often noted in LASEK.⁶ The intact basement membrane may prevent the release of cytokines into the corneal stroma, thereby modulating the wound healing response.⁷ Microfocal damage to the lamina densa of the basement membrane may still occur with epi-LASIK, however, and its clinical significance remains unknown.

RESULTS
Pallikaris et al³ reported results from a study of 44 eyes that underwent epi-LASIK for the correction of low myopia. The investigators found that 38% of the treated eyes had a UCVA of 20/40 or better on postoperative day 1. Sixteen percent of patients reported burning pain during the first postoperative hours, and 97% had clear corneas or trace haze 3 months after treatment. Generally, eyes take longer to heal after epi-LASIK than LASIK, and patients may complain of slightly more pain and blurriness in the initial postoperative period.⁶

The BOTTOM LINE
Although there are several options available to refractive surgeons today, epi-LASIK has the advantage over PRK of reducing postoperative haze and pain while preserving visual outcomes. The former procedure, unlike LASEK, allows surgeons to preserve the epithelial basement membrane. With epi-LASIK, patients' healing rate is slower, and their level of pain is slightly higher than in LASIK. Because it needs no stromal flap, however, epi-LASIK effectively reduces flap-related complications compared with LASIK. It remains to be seen how wavefront technology will affect the outcomes of this new procedure and if changes in postoperative regimens will speed patients' visual recovery.

Reviewer:
Nina Goyal, MD, is a senior resident in ophthalmology at the Rush University Medical Center, Chicago. Dr. Goyal may be reached at ninagoyal@yahoo.com or +1 312 942 5315.

Panel members:
John Chang, MD, is the director of the Guy Hugh Refractive Surgery Centre, Hong Kong Sanatorium and Hospital, Hong Kong. Dr. Chang may be reached at johnchang@hksh.com.
Renée Solomon, MD, is an ophthalmology fellow at Ophthalmic Consultants of Long Island in New York. Dr. Solomon may be reached at rensight@yahoo.com.
Connie Cox, MD, is an ophthalmology fellow at Cleveland Clinic Foundation, Cleveland. Dr. Cox may be reached at Coxc@ccf.org.
Kochoi Wong, MD, is an ophthalmology resident at Isala Clinics, Zwolle, Netherlands. Dr. Wong may be reached at k.wong@isala.nl.