|Year : 2020 | Volume
| Issue : 2 | Page : 623-629
Conventional photorefractive keratectomy vs laser in-situ keratomileusis regarding regression in low myopia at 6-month follow-up
Amin F Amin Ellakwa, Mohamed S Abd Alaziz, Eman M. Abd-Allah El-Asser
Department of Ophthalmology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
|Date of Submission||06-Nov-2019|
|Date of Decision||30-Nov-2019|
|Date of Acceptance||07-Dec-2019|
|Date of Web Publication||27-Jun-2020|
Eman M. Abd-Allah El-Asser
Shebin El Kom, Menoufia
Source of Support: None, Conflict of Interest: None
The aim was to compare between laser-assisted in-situ keratomileusis (LASIK) and conventional photorefractive keratectomy (PRK) regarding postoperative myopic regression after 6 months.
Myopia is a condition in which the refractive power of the eye is greater than required. The most frequent complaint of people with myopia is blurred distance vision, which can be eliminated by refractive surgery procedures such as PRK and LASIK.
Materials and methods
A prospective comparative case series study was conducted on 50 patients with mild to moderate myopia with or without astigmatism, who were divided into two groups: group A included 25 patients operated with PRK and group B included 25 patients operated with LASIK. Follow-up was done by slit lamp and assessment of uncorrected distance visual acuity, manifest refraction, and best spectacle corrected distance visual acuity at 1 week, 1 month, 3 months, and 6 months.
Mean uncorrected visual acuity after 1 week was 0.60 ± 0.11 for the PRK group and 0.84 ± 0.12 for the LASIK group (P < 0.001). Mean uncorrected visual acuity after 1 month was 0.98 ± 0.13 for the PRK group and 0.89 ± 0.13 for the LASIK group (P < 0.002). Mean uncorrected visual acuity after 6 months was 1.07 ± 0.12 for the PRK group and 0.90 ± 0.12 for the LASIK group (P < 0.001). Mean spherical equivalent after 6 months was −0.32 ± 0.22 D for the PRK group and −0.05 ± 0.52 D for the LASIK group (P < 0.024).
Uncorrected visual acuity 1 week after surgery is significantly better in eyes undergoing LASIK than in eyes undergoing PRK. Both procedures provide functional vision by 1 week after surgery. No refractive regression was noted after 6 months of follow-up.
Keywords: excimer laser, laser-assisted in-situ keratomileusis, myopic regression, photorefractive keratectomy, visual performance
|How to cite this article:|
Amin Ellakwa AF, Abd Alaziz MS, El-Asser EM. Conventional photorefractive keratectomy vs laser in-situ keratomileusis regarding regression in low myopia at 6-month follow-up. Menoufia Med J 2020;33:623-9
|How to cite this URL:|
Amin Ellakwa AF, Abd Alaziz MS, El-Asser EM. Conventional photorefractive keratectomy vs laser in-situ keratomileusis regarding regression in low myopia at 6-month follow-up. Menoufia Med J [serial online] 2020 [cited 2020 Jul 16];33:623-9. Available from: http://www.mmj.eg.net/text.asp?2020/33/2/623/287784
| Introduction|| |
Laser vision correction has been widely used for surgical correction of refractive error since refractive surgery was first reported by the Columbian ophthalmologist Barraquer in the early 1960s. Several studies have demonstrated the efficacy and safety of this procedure. Manifest refraction and visual acuity using the Snellen chart have frequently been employed to evaluate the clinical outcomes of these techniques.
The rapid improvement in vision and lack of postoperative pain associated with LASIK has made this the preferred option with patients compared with photorefractive keratectomy (PRK), which has greater postoperative discomfort and prolonged recovery of visual acuity.
Recently, there has been renewed interest in PRK because of increasing concerns of complications associated with LASIK flap creation, including dry eye, corneal ectasia, and flap tears.
Regression is the tendency of an eye to return to its original refraction and is dependent on the preoperative myopia and the amount of correction.
Because myopic regression is difficult to define with a specific value, we defined the regression group as patients having myopia of more than 1 D. According to Hirsch, a myopia of 1 D is ∼6/18 level of visual acuity, which defines the limitation of vision impairment according to the WHO.
A previous study of LASIK reported that the myopic regression for moderate to high myopia was −1.66 ± 2.15 D over 15 years, indicating a regression rate of −0.11 D per year.
This refractive regression seems to be a direct consequence of epithelial hyperplasia. The cornea tends to regularize corneal imperfections to even corneal surface, which is extremely important for maintaining the optical quality. As epithelial hyperplasia is relatively common after refractive procedures, this expected corneal response is already considered in standard nomograms to perform the surgery. The increases in epithelial thickness owing to abnormal keratocyte density and subepithelial deposits are significantly associated with myopic regression.
The increase in epithelial thickness is more persistent and prolonged after PRK than in LASIK. It stabilizes 1 week after LASIK and 1 year after PRK.
The aim of this study was to compare between laser-assisted in-situ keratomileusis (LASIK) and conventional PRK regarding postoperative myopic regression after 6 months.
| Materials and Methods|| |
This is a prospective comparative case series study. The study was conducted on a convenient sample of 50 patients with mild to moderate myopia with or without astigmatism in a private eye–laser center (Tiba Eye Center), Menoufia Governorate, Egypt, by Dr Mohammed Sami Abd Alaziz. The study methods adhered to the tenets of the Declaration of Helsinki for use of human participants in biomedical research and were approved by Ethical Committee of Menoufia Medical College.
Inclusion criteria were age over 18 years, stable refraction more than 1 year, soft contact lens cessation for at least 1 week before examination, minimal corneal thickness of 480 μm, and minimal postoperative residual stromal bed thickness of 350 μm. Exclusion criteria were patients with evidence of forme fruste keratoconus; aged less than 18 years; ocular surface disorders; associated ocular pathologies, for example, cataract or glaucoma; and associated systemic disorders, for example, diabetes or connective tissue diseases.
These patients were divided into two groups: group 1 was treated by LASIK, and group 2 was treated by PRK. All patients were subjected to detailed history and full ophthalmological examination.
Before the study, uncorrected distance visual acuity (UDVA) in decimal, manifest and cycloplegic refractions using Topcon autorefractometer KR900 (Topcon Inc., Tokyo city, Japan), best spectacle corrected distance visual acuity (CDVA), thorough slit lamp examination of anterior and posterior segment, and intraocular pressure measurement using Goldmann applanation tonometer were done. Corneal topography was done utilizing (Allegro Oculyzer; Wave light AG, Erlangen, Germany).
Dilated fundus examination was carried for every patient with slit lamp and Volk 90.
In all eyes, stromal ablation was performed with a Wave Light EX500 Excimer Laser system (Alcon Surgicals, Fort Worth, Texas, USA).
Group 1 eyes were treated by LASIK in which the patient's skin was prepared with povidone iodine (Betadine), and a sterile drape was used over the skin and lashes. Topical Benoxinate hydrochloride (BENOX0.4%, Sterile Ophthalmic Solution; Eipico, Tenth of Ramadan City, Egypt) anesthetic drops were placed in the eye. A lid speculum is placed in the operative eye, and a patch is placed over the fellow eye to avoid cross-fixation. The amount of desired correction, accounting for the vertex distance, is entered into the laser and checked by the surgeon. The patient was asked to fixate on the laser centration light while the surgeon focuses and centers the laser. LASIK flap was created with Moria M2 microkeratome (Moria SA, Antony, France), then lifting the flap was done, and laser ablation was then applied. Repositioning of the flap was done, and then antibiotic drops were applied. Group 2 eyes were treated by PRK in which the epithelium was removed by alcohol 20% using sponge soaked with alcohol for 20 s, and then, the epithelium is removed by PRK spatula exposing stroma. Laser ablation was then applied after introducing the data. Topical mitomycin-C (Mitomycin-C; Kyowa Inc., Chiyoda-ku, Tokyo city, Japan) 0.2 mg/ml was employed in all cases according to diopteric correction, with minimum 20 s and maximum 60 s at the end of the laser exposure followed by generous irrigation of the eye with room temperature-balanced salt solution or ringer lactate. After the surgery, a bandage contact lens was applied.
Postoperative treatments included a broad-spectrum antibiotic eye drop, moxifloxacin 0.5% (Vigamox, Sterile Ophthalmic Solution; Alcon), and a lubricant eye drop, hyaluronic acid (Hyfresh; Jamjoom Inc., Jeddah city, KSA). Topical steroid drops, Prednisolone acetate 1% (PredForte, ophthalmic suspension; Allergan Inc., Irvine, California, USA), were added on the third day postoperative starting with high frequency for 1 week, and then tapered gradually over 2 weeks.
Regarding postoperative follow-up, the first follow-up visit was 5–7 days postoperatively. In this visit, slit lamp examination was done to ensure epithelial healing and exclude any possible complications. Then, bandage contact lens was removed and treatment modified by tapering of corticosteroid.
Then, subsequent visits were at 1 and 3 months postoperative where slit lamp examination was done and record of any adverse events, with assessment of UDVA, manifest refraction, and CDVA.
Finally, at 6-month postoperative follow-up visit, UDVA, manifest refraction, CDVA, thorough slit lamp examination, and corneal topography with corneal wavefront map of the anterior corneal surface obtained from it up to the seventh order of Zernike polynomial at 6 mm diameter were repeated. The data obtained were used for statistical analysis and comparison between the two groups.
Data were collected, tabulated, and statistically analyzed using a personal computer with Statistical Package for the Social Sciences (SPSS) version 20.0 (IBM Corp., Armonk, New York, USA) where the following statistics were applied.
Data were statistically described in terms of mean, SD, median, and range, or frequencies and percentages when appropriate. Preoperative and postoperative values were compared. SD is presented if relevant. P values less than 0.05 were considered statistically significant.
| Results|| |
This study included 50 myopic patients (100 myopic eyes) with or without astigmatism who had LASIK and alcohol-assisted PRK performed to them in the period from January 2019 to July 2019. There were 50 eyes in LASIK group and 50 eyes in PRK group.
The mean age was 27.24 ± 1.84 years, with range of 24.0–30.0 years old in the LASIK group, whereas the mean age was 28.86 ± 2.93 years, with the range of 24.0–35.0 years in the PRK group. There were more males than females in LASIK group, as male constituted 62% of the population, whereas in PRK group, there were more females than males, who constituted 62% of the population [Table 1].
|Table 1: Comparison between the two studied groups according to demographic data|
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Best-corrected visual acuity before surgery had a mean of 0.97 ± 0.04 for all eyes. Preoperative spherical equivalent ranged from −1.25 to −4.50 D, with a mean of −2.56 ± 0.85 D for the eyes undergoing PRK and −2.14 ± 0.59 D for the eyes undergoing LASIK ([Table 2] and [Figure 1]).
|Figure 1: Comparison between the two studied groups regarding visual acuity.|
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The mean uncorrected visual acuity after 1 week in the PRK eyes was 0.60 ± 0.11 and in the LASIK eyes was 0.84 ± 0.12. This difference in visual acuity was significant (P < 0.001). Mean uncorrected visual acuity after 1 month was 0.98 ± 0.13 for the eyes undergoing PRK and 0.89 ± 0.13 for the eyes undergoing LASIK. This difference was highly significant (P < 0.002). Mean uncorrected visual acuity after 3 months was 1.04 ± 0.13 for the PRK group and 0.91 ± 0.12 (20/20) for the LASIK group (P < 0.001). Mean uncorrected visual acuity after 6 months was 1.07 ± 0.12 for the PRK group and 0.90 ± 0.12 (20/20) for the LASIK group (P < 0.001) [Table 3].
The mean preoperative spherical equivalent was −2.14 ± 0.59 D, with range −3.50–1.25 D, in the LASIK group, whereas the mean preoperative spherical equivalent was −2.56 ± 0.85 D, with range −4.50-1.50 D, in PRK group. The mean postoperative spherical equivalent was −0.05 ± 0.52 D, with range of −0.75–1.0 D in LASIK group, whereas the mean postoperative spherical equivalent was −0.32 ± 0.22 D, with range of −0.75–0.25 D, in PRK group (P < 0.024) ([Table 4] and [Figure 2]).
The mean preoperative keratometry reading (K) was 42.32 ± 1.51 and 43.12 ± 1.41 D for both LASIK and PRK groups, respectively. Statistically, there is a highly significant difference (P < 0.01) between preoperative and postoperative keratometry. The mean post-operative keratometry reading (K) was 40.88 ± 1.76 and 40.60 ± 0.91 D for both LASIK and PRK groups, respectively. Statistically, there is no statistical difference (P > 0.05) between LASIK and PRK groups [Table 5].
|Table 5: Comparison between the two studied groups according to K reading|
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The mean predicted error of the patient in LASIK group was −0.06 ± 0.53 D, with minimum of −0.75 D and maximum predicted error of +1.0 D. The mean predicted error of the patient in PRK group was −0.32 ± 0.22 D, with minimum of −0.75 D and maximum predicted error of +0.25 D.
PRK group had significantly higher predicted error than LASIK group.
The mean absolute error of the patient in LASIK group was 0.46 ± 0.27 D, with minimum of 0.0 D and maximum +1.0 D. The mean absolute error of the patient in PRK group was 0.34 ± 0.19 D, with minimum of 0.0 D and maximum of +0.75 D.
The LASIK group had significantly higher mean absolute error than PRK group [Table 6].
|Table 6: Comparison between the two studied groups according to predicted error and mean absolute error 6 months after operation|
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No eyes in the PRK or LASIK group lost two or more lines of best spectacle-corrected visual acuity at 1, 3, or 6 months after surgery.
No intraoperative or postoperative complications were noted in any of the eyes in this study. Specifically, there were no infiltrates, irregular LASIK flaps, flap displacements, clinically significant corneal opacity, or other complications of PRK or LASIK noted in the eyes in this study.
| Discussion|| |
The emerging popularity of LASIK surgery has been driven by the perceived benefits of greater comfort and more rapid visual recovery compared with PRK. Recent studies, however, have shown that long-term visual results are similar with PRK or LASIK in eyes with low myopia.
Importantly, several studies have found that there may be a higher risk of loss of best spectacle corrected visual acuity after 1 year with LASIK than with PRK. In addition, many informed patients wish to avoid potential flap complications that have been estimated to occur in 0.2–5% of eyes undergoing LASIK, depending on the surgeon and the microkeratome.
To our knowledge, no studies have compared early postoperative visual recovery with PRK and LASIK.
In our study, we have noted, however, that most patients with PRK for low myopia have surprisingly good vision at the examination performed after 1 week. We decided to examine the difference in uncorrected visual acuity 1 week, 1 month, 3 months, and 6 months after surgery in eyes undergoing LASIK or PRK for low to moderate myopia so that more reliable information regarding the differences could be provided. Our results confirmed that for low myopia up to ∼5 D, the mean uncorrected visual acuity in eyes undergoing LASIK was significantly better than that in PRK eyes 1 week after surgery. Eyes undergoing LASIK saw an average of one line of Snellen visual acuity better at this visit than did PRK eyes. However, the surprising aspect of this study was the small difference in Snellen visual acuity between the two procedures only 1 week after surgery. Because the manifest refractive error measured after 1 week was similar in the two procedures, the difference in uncorrected visual acuity was likely attributable to surface irregularity remaining in the eyes undergoing PRK that had epithelial healing only a few days before the examination, so refraction in PRK seems to have no effect on visual acuity postoperatively. One month and 6 months after surgery, there was no difference in uncorrected visual acuity between the two groups, with both groups averaging 6/6 uncorrected visual acuity.
A study made by Walker et al. reported that mean uncorrected visual acuity after 6 months was 1.05 ± 0.06 (6/6, logMAR −0.01 ± 0.03) for the PRK group and 1.06 ± 0.05 (20/20, logMAR −0.14 ± 0.03) for the LASIK group (P < 0.41). Mean spherical equivalent after 6 months was 0.02 ± 0.08 D for the PRK group and 0.00 ± 0.08 D for the LASIK group (P < 0.35). No eyes in the PRK or LASIK group lost two or more lines of best spectacle-corrected visual acuity 6 months after surgery.
Hersh et al. report the 6-month outcomes (UCVA, predictability, stability, and haze) of 220 eyes in the moderate to high myopia range that were randomly assigned to PRK or LASIK treatment in a prospective clinical trial. One day after surgery, 4.5% of eyes in the PRK group saw 20/40 or better uncorrected compared with 68.6% in the LASIK group, but at the 6-month follow-up, 66.2% of eyes in the PRK group saw 20/40 or better uncorrected compared with 55.6% in the LASIK group. After PRK, 57.4% were within 1 D of the attempted correction compared with 40.7% in the LASIK group. From 1 to 6 months, there was an average regression of 0.89 D in the PRK group and 0.55 D in the LASIK group.
A study done by Mori et al. reported that regarding the manifest refraction in the LASIK group, the percentages of eyes within ±0.5 or ±1.0 D decreased over time, whereas those in the PRK group remained almost stable. At 3 months, the percentages of eyes within ±0.5 or ±1.0 D in the LASIK group were significantly higher than those in the PRK group.
In other studies of PRK by AlioÂ et al., the regression rates of manifest refraction spherical equivalent (MRSE) from 3 months to 10 years were −0.01 D/year in 225 patients with a mean preoperative MRSE of −3.81 and −0.07 D/year in 267 patients with a mean preoperative MRSE of −8.87 D.
| Conclusion|| |
Short-term follow-up (6 months) for LASIK and PRK demonstrated stable refraction in patients with low myopia. Nevertheless, patients with low myopia who have the opportunity to choose between PRK and LASIK may be advised that uncorrected visual acuity 1 week after PRK is expected on average to be within one line of that obtained with LASIK.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]