The first excimer laser PRK procedure was performed 25 years ago,1 yet it is remarkably still difficult to ascertain which technique is the gold standard for removal of the corneal epithelium. The use of a simple metallic blade or a hockey-stick knife was the first approach described in the 1980s,2 before the revolution of LASIK. The superiority of LASIK in terms of side effects (minimal pain, no haze, and quick recovery) that was recognized in the 1990s was followed by reports of severe flap complications and ectasia. As a result, other epithelial removal techniques such as LASEK and epi-LASIK were developed, in which the epithelium was displaced and then placed back on the cornea after laser ablation. Several studies, however, indicate that removing these epithelial flaps is more efficient than replacing them in terms of healing and pain. Therefore, many surgeons returned to use of the old-fashioned hockey-stick knife or the Amoils brush. More recently, the use of a single-step excimer laser procedure that includes ablation of the epithelium has been described.3
This article describes the use of a disposable device for a new concept of corneal epithelial ablation: epi-Bowman keratectomy (EBK). Our goal was to develop a simple, single-use, nonmetallic instrument that could be used to remove all of the epithelium and collect it without debris; it was also necessary that the instrument preserve the integrity of the Bowman layer and the stroma, as debris, incomplete ablations, and scratches on these structures can yield refractive consequences.
To perform EBK, we designed a bowl-shaped, doublebladed instrument made with a biocompatible polymer (Epi Clear, Orca Surgical; Figure 1), which gently sweeps away the epithelium and contains discarded epithelial cells for safe and complete removal from the treatment bed. The disposable instrument head is mounted from a cartridge onto an ergonomic titanium handle. The Epi Clear resembles a plastic hockey-stick knife, with a special double asymmetric design.
METHODS AND ANALYSIS
To test the efficacy of our approach, we conducted a nonrandomized, comparative clinical study of our first patients treated with EBK (EBK group) and patients treated with PRK (PRK group). The EBK group included 20 eyes of 10 myopic patients (age range, 19–27 years; spherical equivalent range, -1.75 to -7.25 D). The PRK group included 89 eyes of 46 myopic patients (age range, 18–29 years; spherical equivalent range, -1.00 to -8.50 D). Our standard PRK procedure combined a partial excimer laser ablation (35-μm phototherapeutic keratectomy), followed by manual scrubbing with a hockey-stick knife. The same surgeon (Dr. Taieb) performed all surgeries using the WaveLight Allegretto 400-Hz laser (Alcon Laboratories, Inc.).
Postoperatively, patients received a soft bandage contact lens and four types of eye drops: dexamethasone, a fluoroquinolone, artificial tears, and 0.04% oxybuprocaine. Each patient was asked to use the anesthetic drops only in the event of severe pain and to record the number of daily applications (maximum permitted five times per day). Follow-up was performed on days 1, 2, 3, and 7.
The procedure was evaluated in terms of duration and efficacy of EBK versus PRK. The epithelial ablation zone (EAZ) quality was assessed in terms of amounts of debris, EAZ border regularity, and the integrity of the Bowman layer and the stroma. We analyzed patient recovery using three parameters: (1) the duration of reepithelialization, (2) pain intensity, based on the number of anesthetic drops used, and (3) visual recovery in the early postoperative days.
We found that EBK with the Epi Clear was technically easy to perform, and the mean procedure time was 10 seconds (range, 7–20 seconds). The surgeon controls the size of the EAZ using the size of the head of the device (9 mm) and scrapes the epithelium layer by layer until reaching the Bowman layer, which looks bright and smooth. The corneal surface must be dry, and a wide eyelid aperture is necessary in order to keep the tears far enough from the corneal surface to be ablated. It seems impossible to scratch the Bowman layer using this technique.
Using circular or up-and-down movements, it is easy to produce a rather regular round or ovoid EAZ shape using the Epi Clear. The residual borders of the EAZ have a graded aspect, with one or two steps of epithelial basement membrane. This device collects the debris of the scraped epithelium, and we did not have to clean the EAZ before the laser procedure.
Patient recovery is characterized by a significant decrease in ocular pain during the early days after surgery. In patients who underwent EBK, the mean number of anesthetic drops used was 1.6 on day 1 and 0.5 on day 2, compared with 4.2 and 3 drops, respectively, in the control group. The percentage of patients who complained of significant pain was 25% on day 1 and 10% on day 2 in the EBK group, versus 75% and 40%, respectively, in the control group. Rates of complete closure of the epithelium within 48 hours were higher as well: 95% in the EBK group and 40% in the PRK group. The mean binocular UCVA was 20/40 for both groups once the epithelium was closed.
Removal of the epithelium is a simple but crucial step in performing a successful surface ablation refractive surgery. Refractive precision requires a smooth, unscratched EAZ without epithelial debris. It is important to note that 10 μm of ablated corneal tissue has a refractive value of about 1.00 D, and the Bowman layer thickness is 14 μm.
Healing time and visual recovery are quicker with a preserved Bowman layer and without alcohol toxicity, debris, and scratches. Regular concentric borders of the EAZ are also an important factor. Corneal pain, the main side effect of epithelial removal, is a direct consequence of the geometric characteristics of the erosion, corneal foreign bodies (epithelial debris), scratches, and nerve irritation after mechanical rubbing or alcohol or excimer laser use. All of these are contributing factors to haze formation.4
Based on our early clinical results, we were encouraged to continue using the Epi Clear. Since our initial study of the first 10 treated patients, the device has been used to treat many other patients with the same positive clinical impression.
EBK has a short learning curve. We always achieved a good EAZ quality followed by a marked reduction in pain and a shorter healing time compared with conventional epithelial removal. The main factor in these differences seems to be the integrity of the Bowman layer, which is gently rubbed by the plastic device rather than scraped with a metallic hockey-stick knife, abraded by the toxicity of alcohol, or overablated by the excimer laser.5 Moreover, with EBK, a larger amount of Bowman layer is preserved in comparison with alcohol-prepped or single-step all-surface laser ablation procedures. With an EAZ diameter of 8.5 mm, 57 mm2 of Bowman layer is affected, compared with 38 mm2 with the EBK device, as the mean treatment diameter within the EAZ is only 7 mm.
We may also suppose that in the periphery of the optical ablation zone, the peripheral corneal innervation may be preserved under the untouched peripheral Bowman layer.5 Combined with the controlled removal of the epithelium from the EAZ layer after layer creating graded borders, this could help explain the lower postoperative eye sensitivity. The procedure appears to be accurate and safe, with no injury to the Bowman layer or the stroma and removal of all epithelium.
EBK for surface ablation in refractive surgery seems to be precise, safe, and easy to perform. It provides fast patient recovery and satisfactory visual function within 48 hours on average. Following these encouraging results, other studies have begun in various centers in Europe.
The Epi Clear has received the Conformité Europeénne (CE) Mark. The device is not cleared or approved by the US Food and Drug Administration for investigational use or for sale in the United States.
Matsliah Taieb, MD, is an ophthalmologist in a private ophthalmology center in Rishon Le-Zion, Israel. Dr. Taieb has a financial interest in the product mentioned in this article. Dr. Taieb may be reached at e-mail: firstname.lastname@example.org.
Yariv Bar-On, OD, is an optometrist and the Chief Executive Officer of Orca Surgical. Dr. Bar-On has a financial interest in the product mentioned in this article. Dr. Bar-On may be reached at e-mail: email@example.com.
Andrew Fink, MD, is an ophthalmologist in a private ophthalmology center in Rishon Le-Zion, Israel. Dr. Fink has no financial interest relevant to the content of this article. Dr. Fink may be reached at e-mail: firstname.lastname@example.org.
Yishay Falick, MD, MBA, is an ophthalmologist in the Cornea Service Unit at Rabin Medical Center, Petah Tikva. Dr. Falick has no financial interest relevant to the content of this article. Dr. Falick may be reached at e-mail: email@example.com.
- Seiler T, Bende T, Wollensak J. Laser surgery of the cornea. [Article in German] Fortschr Ophthalmol. 1987;84(6):513-518.
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- Wilson SE, Mohan RR, Mohan RR, Ambrósio R Jr, Hong J, Lee J. The corneal wound healing response: cytokinemediated interaction of the epithelium, stroma, and inflammatory cells. Prog Retin Eye Res. 2001;20(5):625-637.
- Lagali N, Germundsson J, Fagerholm P. The role of Bowman’s layer in corneal regeneration after phototherapeutic keratectomy: a prospective study using in vivo confocal microscopy. Invest Ophthalmol Vis Sci. 2009;50(9):4192-4198.