THE BIRTH OF Epi-LASIK
The goal of refractive surgery has remained unchanged during the past decades: to provide patients with the best possible UCVA with 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 previously presented by PRK. The downside to this procedure is that refractive 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, LASIK combines the principles employed in both PRK and LASIK.3 Surgeons apply a diluted alcohol solution, which allows the removal of the corneal epithelial layer as a continuous sheet, and create an epithelial flap. After performing photoablation of the corneal surface, the ophthalmologist replaces the epithelial sheet onto the corneal surface. This step is considered to have a beneficial effect on wound healing.4,5 However, according to Pallikaris et al,6 the use of 15% and 20% alcohol solutions to obtain epithelial disks resulted in the formation of cytoplasmic fragments of the basal epithelial cells, an enlargement of intercellular spaces, and discontinuities in the basement membrane. If the epithelial sheet could be separated without the use of alcohol, the epithelial flap might remain viable and provide faster recovery and less haze.
The term epi-LASIK refers to a new approach in refractive surgery. Instead of a bladed microkeratome, the surgeon uses an epikeratome with a blunt plastic blade to mechanically separate 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 blade or alcohol, thereby 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, and 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, in which 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 However, microfocal damage to the lamina densa of the basement membrane may still occur in some eyes with epi-LASIK, and its clinical significance remains unknown.
In May 2005, Pallikaris et al3 reported results from a study of 44 eyes of patients who 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, 16% of patients reported burning pain during the first postoperative hours, and 97% had clear corneas or trace haze 3 months after treatment. In general, however, 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 than they do after LASIK.6
The benefits of epi-LASIK may include the lack of late-onset corneal haze6 as opposed to PRK, although the long-term results of epi-LASIK in high myopes are currently unavailable. A flap, which can be as thick as 200µm, is unneeded for epi-LASIK. As a result, more tissue is available for ablation in this procedure than LASIK, so the former treatment option could be advantageous for high myopes.
Although there are several options available to refractive surgeons today, epi-LASIK has the advantage of reducing postoperative haze and pain while preserving visual outcomes when compared with PRK. The former procedure allows surgeons to preserve the epithelial basement membrane, unlike LASEK. 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.
Nina Goyal, MD, may be reached at (312) 942-5315; email@example.com.
Y. Ralph Chu, MD, is Medical Director, Chu Vision Institute in Edina, Minnesota. He may be reached at (952) 835-1235; firstname.lastname@example.org.
Wei Jiang, MD, is a resident in ophthalmology at the Jules Stein Eye Institute in Los Angeles. She may be reached at (310) 825-5000; email@example.com.
Baseer Khan, MD, is a senior resident in ophthalmology in the Department of Ophthalmology at the University of Toronto. He may be reached at (415) 258-8211; firstname.lastname@example.org.
Patty Lin, MD, MBA, is a resident in ophthalmology at the Jules Stein Eye Institute in Los Angeles. She may be reached at (310) 825-5000; email@example.com.
Gregory J. McCormick, MD, is a cornea and refractive fellow at the University of Rochester Eye Institute in New York. He may be reached at (585) 256-2569; firstname.lastname@example.org.
Jay S. Pepose, MD, PhD, is Professor of Clinical Ophthalmology & Visual Sciences, Washington University School of Medicine, St. Louis. He may be reached at (636) 728-0111;
Paul Sanghera, MD, is a senior resident in ophthalmology in the Department of Ophthalmology and Vision Sciences at the University of Toronto. He may be reached at (416) 666-7115; email@example.com.
Renée Solomon, MD, is an ophthalmology fellow at Ophthalmic Consultants of Long Island in New York. She may be reached at firstname.lastname@example.org.
Tracy Swartz, OD, MS, may be reached at (615) 321-8881; email@example.com.
Ming Wang, MD, PhD, may be reached at (615) 321-8881; firstname.lastname@example.org.