|Year : 2014 | Volume
| Issue : 1 | Page : 1-4
Transepithelial photorefractive keratectomy versus conventional alcohol-assisted photorefractive keratectomy for correction of mild and moderate myopia
Waleed A Ghobashy, Mohamed E Shahin, Karem A Kolkailah
Department of Ophthalmology, Suez Canal University, Ismailia, Egypt
|Date of Submission||30-Sep-2013|
|Date of Acceptance||24-Jan-2014|
|Date of Web Publication||21-Jun-2014|
Waleed A Ghobashy
MD, Faculty of Medicine, Suez Canal University, 41511, Ismailia
Source of Support: None, Conflict of Interest: None
The aim of the study was to compare both transepithelial photorefractive keratectomy (trans-PRK) and PRK for correction of mild and moderate myopia with respect to effectiveness, visual recovery pain, and safety.
Materials and methods
In this prospective case-control series, group I with 24 myopic eyes (12 patients) with spherical equivalent -1.00 to -6.00 D underwent trans-PRK using Schwind Amaris 500E excimer laser, with trans-PRK plate form. A case-adjusted group II (the control group) with 24 myopic eyes (12 patients) with spherical equivalent -1.00 to -6.00 D underwent alcohol-assisted PRK using Visx S4 excimer laser. Uncorrected visual acuity (UCVA) was measured on the first day, at first week, 1 month, and 6 months along with manifest refraction. Postoperative pain was assessed using visual analog scale. Occurrence of complications was documented.
Patients in group I showed faster visual recovery with a mean UCVA of 0.3 on the first postoperative day compared with those in group II (0.2); however, both groups reached a mean UCVA of 0.9 by the end of sixth month. Manifest refraction was comparable in both groups. Pain was significant in group II with a score of 4 on the first day declining to 0 by the end of the first week compared with group I with a mean pain score of 3 on the first day and 0 by the end of day 4. No complications were recorded in either of the two groups along the study time.
Trans-PRK may offer a safe, less painful, and effective alternative to alcohol-assisted PRK in the treatment of mild and moderate myopia, especially in cases of thin cornea.
Keywords: Trans-epithelial photorefractive keratectomy, photorefractive keratectomy, myopia
|How to cite this article:|
Ghobashy WA, Shahin ME, Kolkailah KA. Transepithelial photorefractive keratectomy versus conventional alcohol-assisted photorefractive keratectomy for correction of mild and moderate myopia. J Egypt Ophthalmol Soc 2014;107:1-4
|How to cite this URL:|
Ghobashy WA, Shahin ME, Kolkailah KA. Transepithelial photorefractive keratectomy versus conventional alcohol-assisted photorefractive keratectomy for correction of mild and moderate myopia. J Egypt Ophthalmol Soc [serial online] 2014 [cited 2017 Jun 27];107:1-4. Available from: http://www.jeos.eg.net/text.asp?2014/107/1/1/134922
| Introduction|| |
Photorefractive keratectomy (PRK) was the first kind of corrective eye surgery to use a laser rather than a blade to remove corneal tissue. Utilizing excimer laser which was developed in the early 1970s and modified for ophthalmic use in the early 1980s. PRK became less popular following the development of LASIK, a procedure that allowed patients to have their vision corrected without the need for extended recovery from surgery . This was encouraged by the recognizable cost-effectiveness of keratorefractive surgery, which gained a momentum by the invention of LASIK in early 1990s. However, the limitations of LASIK, such as limited available corneal thickness and the potential flap-related concerns, demanded the era of surface ablation to emerge as an alternative. The photorefractive keratectomy (PRK)-associated discomfort such as relative delayed visual recovery and the potential haze development  are still significant concerns for both surgeons and patients in taking the decision of performing PRK. Trans-PRK is a relatively new modification of the conventional PRK in which the epithelial removal is achieved by an excimer laser instead of alcohol and manual scraping. This is supposed to create a smoother crater allowing relative rapid healing of the epithelium with a resulting faster visual recovery and less discomfort . With these issues in mind, we designed this study to measure visual outcome, postoperative pain, and occurrence of complications among patients with mild and moderate myopia treated by LASIK and trans-PRK and to determine whether one procedure offers any advantages or disadvantages over the other .
| Materials and methods|| |
Patients with systemic or ocular disease that may interfere with the healing process of the cornea, such as rheumatoid arthritis, dry-eye syndrome, anterior or posterior uveitis, keratoconus, corneal dystrophy or degeneration, glaucoma, retinal diseases, lens opacity, history of severe ocular trauma, and previous ocular surgery, were excluded from the study.
This was a prospective case-control study. Group I included 24 myopic eyes (12 patients) with spherical equivalent -1.00 to -6.00 D. They were subjected to trans-PRK using Schwind Amaris 500E excimer laser (Schwind Eye-Tech, Kleinostheim, Germany), with trans-PRK plate form (both epithelial removal and ametropia are performed in a single step) and 500-Hz excimer laser (spot size of 0.54 mm and active 5 D eye tracking) after standard disinfection and ocular draping with instillation of topical benoxinate hydrochloride 0.4% as a topical anesthetic.
A case-adjusted group II (the control group) included 24 myopic eyes (12 patients) with spherical equivalent -1.00 to -6.00 D; they underwent PRK using Visx S4 excimer laser (Abbott Medical Optics Inc., Santa Ana, CA, USA), with PRK platform. After standard disinfection and ocular draping with instillation of topical benoxinate hydrochloride 0.4% as a topical anesthetic, the cornea was exposed to 20% ethyl alcohol for 15 s with the aid of a well. Thereafter, epithelium was removed manually in a centripetal manner using a blunt hockey blade. The diameter of epithelial removal was 8 mm . Then, 1050-Hz excimer laser, with variable beam sizes from 0.65 to 6.5 mm, was used to achieve the desired ametropia.
For both groups, a topical application of mitomycin-C 0.02% (0.2 mg/ml) diluted in balanced salt solution was instilled in each eye, with a microsponge placed over the ablated stroma for 15-30 s immediately after laser ablation . The corneal surface and the entire conjunctiva were then vigorously irrigated with 20 ml cold balanced salt solution to remove the residual mitomycin-C. At the end of the procedure, a bandage contact lens was applied followed by one drop of tobramycin-dexamethasone suspension 0.1%.
In both groups, patients were instructed to use topical prednisolone acetate suspension 1% four times daily, tapered over 4 weeks according to corneal haze and intraocular pressure, ketorolac tromethamine ophthalmic solution 0.4% three times daily for 2 weeks, moxifloxacin hydrochloride ophthalmic solution 0.5% four times daily for 1 week, and ibuprofen 400 mg tablet orally twice daily for 4 days .
Bandage contact lens was removed on the fourth to sixth postoperative day, guided by epithelial healing and patient's comfort.
Uncorrected visual acuity (UCVA) and best-corrected visual acuity were measured using the Snellen chart on the first day, at first week, 1 month, and 6 months along with manifest refraction by retinoscopy. Postoperative pain was assessed using visual analog scale . Occurrence of complications was documented.
At the first postoperative week, all patients were examined with a slit lamp, and the area of the epithelial defect was measured with its ruler to identify the time of complete healing.
For evaluation of haze, we used Hanna's grading scale from 0 (no haze) to 4+ (dense white corneal haze) .
Decimal values for UCVA and BCVA were used for statistical purposes. Preoperative central corneal thickness, preoperative and postoperative K-readings, optical zone of ablation, depth of ablation, and residual stromal thickness were documented using Sirius 3D corneal analysis, merging Scheimpflug technology with Placido topography (Costruzioni Strumenti Oftalmici, Scandicci Firenze, Italy).
Mean, SD, and correlation coefficient were calculated for variables, with paired Student's t-test as significance test. P value less than 0.05 was considered statistically significant.
| Results|| |
Forty-eight eyes of 24 patients were included in this study and were assigned into two groups. Group I with 24 myopic eyes of 12 patients with a mean UCVA of 0.15 ± 0.05 underwent trans-PRK, eight (75%) of the patients in this group were female individuals. Group II with 24 myopic eyes of 12 patients with a mean UCVA of 0.13 ± 0.08 underwent alcohol-assisted PRK, eight (75%) of the patients were female individuals.
Preoperative data are listed in [Table 1] and [Table 2].
In group I, contact lens was removed in average by the fifth postoperative day, and there was a strong negative correlation (-0.946) between the depth of ablation and the period needed to achieve healing of the epithelium. In group II, contact lens was removed in average by the sixth postoperative day, and there was a strong positive correlation (+0.929) between the depth of ablation and the period needed to achieve healing of the epithelium.
There was a strong positive correlation (+0.904) between wider optical zone and postoperative pain on the first postoperative day in group II.
Postoperative data are shown in [Table 3].
The UCVA was significantly better in group I on the first day, with a mean of 0.7 ± 0.23. By the end of the first week, there was no significant difference between the two groups regarding UCVA. This continued to the end of the study.
Pain was significantly worse in group II by the end of the first week, with a mean score of 0.75 ± 0.96; however, the difference between both groups was insignificant by the end of the first postoperative month.
Minimal and insignificant haze was noticed in patients in both group I and group II that tend to fade away by the end of the sixth month of the study.
No complications were recorded in any of the patients between the two groups.
| Discussion|| |
This study suggests that trans-PRK as well as alcohol-assisted PRK are effective procedures for the correction of mild and moderate myopia. Although the trans-PRK group I showed superior visual results during the early postoperative period, there was no statistically significant difference in the outcomes of UCVA by 6 months. Similar results were obtained by Hatch and colleagues ,,,, as they compared PRK with thin-flap LASIK regarding visual outcome. Our visual outcome is better than that obtained by Wang et al. , as 80% of trans-PRK eyes in our study achieved UCVA of 1.00 by the end of the first postoperative month compared with only 39% of the patients in their study; this shows the superior outcome to the single-step trans-PRK provided by Schwind Amaris 500E compared with the older Schwind ESIRIS that utilized phototherapeutic keratectomy (PTK) mode followed by PRK in Wang's study. Another older study carried out by Clinch et al.  to compare trans-PRK with mechanical removal of epithelium showed more humble results, with only 17.9% of patients in the trans-PRK group reaching UCVA of 1.0 by the end of the first postoperative month. This may be because of control of corneal haze by adjuvant use of intraoperative mitomycin-C in our study.
Emmetropia (±0.5 D) was achieved in all patients included in the study by the end of the sixth postoperative month. These results are comparable with results declared by Wang and colleagues ,.
Pain was significantly worse in the PRK group II with an average score of 3.2 ± 1.1 until the end of the first postoperative week, and then subsided markedly such that no significant difference in pain was observed between the two groups later. Similar average pain (3 ± 1.2) score was found by Buzzonetti et al. , as they utilized Nidek CXIII excimer laser (Fremont, CA, USA) to perform trans-PRK.
Haze was not a significant issue in both groups; it never exceeded the score of 2 (group II), and in all patients it regressed to a level below score 1 by the end of the study. This could be explained by the routine use of intraoperative mitomycin-C in these patients as well as by the smoother surface created by laser removal of epithelium. These results could be compared with those obtained by Hashemi et al. , with slight higher score of haze (score 3).
| Conclusion|| |
Trans-PRK may offer a safe and effective alternative to PRK in the treatment of mild and moderate myopia, especially in cases of thin cornea, with superior comfort and early visual recovery only limited to the early postoperative week.
| Acknowledgements|| |
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]