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Year : 2020  |  Volume : 33  |  Issue : 4  |  Page : 1171-1177

Transepithelial photorefractive keratectomy for myopic astigmatism in comparison with conventional photorefractive keratectomy

1 Department of Ophthalmology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Ophthalmology, Shebin El-Kom Ophthalmology Hospital, Menoufia, Egypt

Date of Submission14-Mar-2020
Date of Decision06-Apr-2020
Date of Acceptance12-Apr-2020
Date of Web Publication24-Dec-2020

Correspondence Address:
Heba S Shetaih
Shebin El-kom, Menoufia 32717
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mmj.mmj_66_20

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To compare the outcomes of transepithelial photorefractive keratectomy (Trans-PRK) with those of conventional photorefractive keratectomy (PRK) with respect to the postoperative pain, healing time, visual acuity recovery, and haze.
PRK was the first of a kind of corrective eye surgery to use a laser rather than a blade to remove corneal tissue. Trans-PRK, where both the epithelium and stroma are removed in a single step, is a relatively new procedure of laser refractive error correction.
Patients and methods
A prospective comparative nonrandomized study was conducted, where patients with low to moderate myopia with or without astigmatism were assigned to the Trans-PRK group or the PRK group. In the Trans-PRK group, eyes were treated using the Amaris excimer laser. Outcome measures included postoperative pain using a pain questionnaire, epithelial healing time, uncorrected visual acuity, and corneal haze, which were compared between the study groups.
The mean subjective postoperative pain score (2, indicating hurts little more) at 48 h was 2.26 in Trans-PRK group (97 eyes) and 2.38 in PRK group (97 eyes) (P = 0.369). The mean ± SD time to complete epithelial healing was 2.25 ± 0.6 days and 3.43 ± 0.8 days, respectively (P < 0.001). At 1 week, first month, and third month, the uncorrected visual acuity postoperatively was statistically significantly better in Trans-PRK; however, corrected visual acuity or manifest refraction between the groups was not significant. Haze was significantly less in Trans-PRK group (P = 0.007).
Trans-PRK may offer an effective and easier platform than conventional PRK in the treatment of mild and moderate myopia, and patients have better visual outcome, faster healing time, and less postoperative haze.

Keywords: myopia, photorefractive keratectomy, transepithelial photorefractive keratectomy

How to cite this article:
Ellakwa AF, Abd El-Aziz MS, Shetaih HS. Transepithelial photorefractive keratectomy for myopic astigmatism in comparison with conventional photorefractive keratectomy. Menoufia Med J 2020;33:1171-7

How to cite this URL:
Ellakwa AF, Abd El-Aziz MS, Shetaih HS. Transepithelial photorefractive keratectomy for myopic astigmatism in comparison with conventional photorefractive keratectomy. Menoufia Med J [serial online] 2020 [cited 2021 Apr 19];33:1171-7. Available from: http://www.mmj.eg.net/text.asp?2020/33/4/1171/304514

  Introduction Top

Photorefractive keratectomy (PRK) has commonly been used as an effective, safe, and reasonable method for treatment of patients with low to moderate myopia since 1983[1].

Moreover, PRK is appropriate for patients with refractive errors who are not eligible candidates for laser in-situ keratomileusis (LASIK) owing to thin corneas, subtle topographic irregularities, and epithelial basement membrane disease[2].

Corneal haze, epithelial healing irregularity, and pain are known adverse effects of PRK[3]. Transepithelial photorefractive keratectomy (Trans-PRK) using Amaris excimer laser is a modified and alternative method to conventional PRK[4]. The unique feature of this technique is that it can be applied as a one step, nontouch surgery using the trans-PRK Nomo-gram of the Amaris laser, with minimum induced trauma to the eye, and in an attempt to overcome the drawbacks of postoperative pain, corneal haze, and irregular epithelial healing associated with the PRK procedure[5].

  Patients and Methods Top

Study design

This was a prospective comparative case series study conducted in private eye-laser centers (Tiba and Alhekma centers), Menoufia governorate, Egypt. 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.

Study population

A total of 100 patients (194 myopic eyes) with or without astigmatism who met the eligibility criteria were enrolled in the study after well-informed consent. This sample was divided into two groups. Each group included 100 patients. Group 1 included 50 patients who underwent Trans-PRK, and group 2 included 50 patients who underwent alcohol-assisted PRK

Inclusion criteria was restricted to those 18 years old or older with stable refraction for more than 1 year; off soft contact lens for a minimum of 14 days before preoperative examination; mild myopia, with spherical equivalent refraction of −0.50 to −3.00 D; and moderate myopia, with spherical equivalent refraction between −3.25 and −6.00 D in at least one eye.

Exclusion criteria were ocular diseases, such as severe dry eye, blepharitis, corneal disease, contact lens warpage, cataract, uveitis, and posterior segment anomalies involving the macula or optic nerve; any of the systemic conditions, such as diabetes mellitus and connective tissue disease; pregnancy; or nursing. Moreover, any patient who had previous ocular surgery including keratorefractive surgery was excluded.

Preoperative assessment

Before the study, all patients had a complete preoperative eye examination including uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) by decimal chart, manifest and cycloplegic refractions by autorefractometer RM 8000, slit lamp biomicroscopy to evaluation of the anterior segment and the fundus, and applanation tonometry. The preoperative refractive workup corneal topography was done using Schwind Sirius (SCHWIND eye-tech-solutions, Mainparkstraße 6-10, 63801 Kleinostheim, Germany) to Trans-PRK patients and WaveLight Allegretto Oculyzer to alcohol-assisted (AA-PRK) patients. Soft contact lenses were discontinued for a minimum of 14 days before examination and treatment.

Surgical technique

Two surgeons performed the cases (Amin Faisal and Mohammed Sami). The standard preoperative procedure for conventional PRK and Trans-PRK was the same. The eyes were then scrubbed and draped, and a closed-loop lid speculum equipped with suction was placed. The other eye was occluded.

In Trans-PRK group, the epithelium and stroma were ablated in a single step using the Trans-PRK Nomo-gram of the Amaris laser's ORK-CAM software.

In PRK group, 20% ethyl alcohol in a 9.0-mm well was placed on the cornea for 20 s. The cornea was rinsed with a balanced salt solution.

The laser treatment was delivered using the ablation profile of the laser's software. In both groups, the optical zone varied between 6.00 and 7.00 mm. The transition zone was calculated using the Nomo-gram based on the patient's age, refractive error, and K readings; it varied between 0.36 and 2.24 mm. The laser treatment was centered on the pupillary axis. After laser ablation, a high-oxygen-content (50%) soft contact lens was placed on the cornea and one drop each of a topical antibiotic agent, steroidal agent, and NSAID was given.

Postoperative care and follow-up were as follows: patients were given prednisone drops and gatifloxacin drops five times a day, NSAID drops three times a day, and preservative-free artificial tears every hour. NSAID drops were discontinued after 1 week, but betamethasone eye drops were tapered off over 4–6 weeks. Patients were followed up until the corneal epithelium completely healed.

Epithelial healing was assessed using the slit lamp. The therapeutic contact lens was removed if there was no epithelial defect. Postoperatively, visual acuity (expressed in decimal) and refractive outcomes were analyzed at the first month and third month. The pain score they had experienced at the postoperative day 2 was measured using a five-point present pain scale. The pain questionnaire expresses the pain level on faces pain scale[6]. Accordingly, pain severity was scored as follows: 0 = no pain, 1 = hurts a little bit, 2 = hurts a little more, 3 = hurts even more, 4 = hurts a whole lot, and 5 = hurts the worst. Corneal haze was graded according to a study by Alió et al.[7] as follows: 0 = no haze, 0.50 = trace haze on oblique illumination, 1 = corneal cloudiness not interfering with the visibility of fine iris details, 2 = mild dimness of fine iris details, 3 = moderate obliteration of iris details, and 4 = details of the lens and iris not discernible. Visual acuity and refractive outcomes were performed at week 1 and months 1 and 3 postoperatively.

Statistical analysis

Data were fed to the computer and analyzed using IBM SPSS software package, version 20.0.(IBM Corp., Armonk, New York, USA). Qualitative data were described using number and percent. The Kolmogorov–Smirnov test was used to verify the normality of distribution. Quantitative data were described using range (minimum and maximum), mean, SD, and median. Significance of the obtained results was judged at the 5% level.

  Results Top

This study included 100 myopic patients (194 myopic eyes) with or without astigmatism who had Trans-PRK and PRK performed to them: 97 eyes in Trans-PRK group and 97 eyes in PRK group.

The mean age in Trans-PRK group was 26.70 ± 5.11 years, with range of 20–36 years, whereas in PRK group, the mean age was 28.02 ± 4.90 years, with range of 20–38 years. There were more females than males in both groups [Table 1].
Table 1: The demographic distribution of the studied patients

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Mean preoperative spherical equivalent refraction was −3.03 ± 1.05 D in the Trans-PRK group and −2.28 ± 1.26 D in the PRK group (P < 0.001).

There was a statistically significant difference in the sphere and UCVA (in decimal) between the two groups (P = 0.001 and P < 0.001, respectively).

Mean preoperative astigmatism was −1.74 ± 1.59 D in Trans-PRK and −1.33 ± 0.91 D in PRK (P = 0.429), with no statistically significant difference [Table 2].
Table 2: Comparison between transepithelial photorefractive keratectomy and photorefractive keratectomy according to refractive outcome postoperative at first and third month

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Mean preoperative BCVA (in decimal) was 0.97 ± 0.05 in the Trans-PRK group and 0.95 ± 0.10 in the PRK group (P = 0.500), with no statistically significant difference [Table 3].
Table 3: Comparison between best-corrected visual acuity preoperatively and uncorrected visual acuity postoperatively in each group

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The mean time of complete epithelial healing was significantly shorter in the Trans-PRK group (2.25 ± 0.60 days) as compared with the PRK group (3.43 ± 0.80 days) (P ≤ 0.001) [Figure 1].
Figure 1: Comparison between the two studied groups according to postoperative healing epithelium.

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The mean subjective postoperative pain score at 48 h was not statistically significant different between the study groups (P = 0.369) [Figure 2].
Figure 2: Comparison between the two studied groups according to postoperative pain level at 48 h.

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After 1 week, 1 month, and 3 months, the mean UCVA was significantly better in the Trans-PRK group than in the PRK group (P ≤ 0.001) [Table 4].
Table 4: Comparison between the different periods according to visual acuity postoperatively

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Most eyes were below grade 2 in all patients regarding subepithelial haze [Figure 3].
Figure 3: Comparison between the two studied groups according to haze grade.

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In the Trans-PRK group, spherical refraction decreased from −3.69 ± 1.88 to 0.18 ± 0.36 and astigmatism decreased from −1.74 ± 1.59 to −0.02 ± 0.39 D at the third month postoperatively. In the PRK group, spherical refraction decreased from −2.96 ± 2.36 to −0.16 ± 0.57 D and astigmatism changed from −1.33 ± 0.91 to −0.24 ± 0.43 D after the third month of surgery. There were significant differences in the mean spherical refraction and astigmatism between the two groups postoperatively (P < 0.001).

In the transepithelial group, 3-month postoperative result showed a higher statistically significant association of UCVA within ±1 line of the preoperative BCVA (P < 0.001), and there was no statistical significant difference (P = 0.433) in the PRK group [Table 3]. Despite this no significant difference in PRK group, the visual outcome was satisfactory in this group.

  Discussion Top

Few direct comparisons between single-step Trans-PRK and conventional PRK have been published so far. Meanwhile, the procedure has undergone several minor modifications and Nomo-gram adjustments[8]. Thus, there is a need for updated comparative evaluations based on a larger number of eyes.

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[9].

In the present study, the comparison between the two studied groups according to postoperative pain level at 48 h by using questionnaires revealed that there was no statistical significant difference between two groups regarding pain level, where mean ± SD pain score in Trans-PRK was 2.26 ± 0.60 and in PRK group was 2.38 ± 0.49.

In harmony with our findings, Kaluzny et al.[10] reported that the mean pain scores after the surgery were 4.78 ± 2.65 in the Trans-PRK group and 4.59 ± 2.85 in the AA-PRK group (P = 0.85). There were also no differences in pain intensity during first days after the surgery (mean scores of 4.46 ± 2.54 and 4.51 ± 2.36 in the Trans-PRK and AA-PRK groups, respectively; P = 0.86).

Contrary results to our findings were reported by the study of Bakhsh et al.[11], which demonstrated decreased mean postoperative pain scores in Trans-PRK than the AA-PRK group, with statistically significant difference at day 1, day 3, and week 1 (P < 0.001); by the study by Fadlallah et al.[5], in which the patients' postoperative pain score at 48 h was less in the Trans-PRK group; by the study by Celik et al.[12]; and by the study by Kanitkar et al.[13], in which their patients' pain score is less in AA-PRK than in the Trans-PRK group.

Regarding healing epithelium, the present study demonstrated the Trans-PRK group had a shorter epithelial healing time than the conventional PRK group postoperatively (P < 0.001). The mean ± SD time to complete epithelial healing was 2.25 ± 0.6 days and 3.43 ± 0.8 days, respectively.

The present study is in harmony with the study of Bakhsh et al.[11], which reported that complete corneal epithelial healing time was shorter in Trans-PRK than the AA-PRK group. This was probably owing to the uniform, precise, and smooth epithelial treatment, and the area removed was the same as that of the treated zone in the Trans-PRK, which is in contrast to the area removed in AA-PRK, where it was larger than the treated zone by laser. Similar results were obtained by Lee et al.[14], in which they reported that laser epithelial removal is the shortest in healing time among the three epithelial removal techniques (mechanical, alcohol-assisted, and excimer LASER). Moreover, similar results were obtained by Fadlallah et al.[5], in which they reported 2.5 ± 0.6 and 3.7 ± 0.8 days, respectively (P = 0.01).

Similarly, the study by Naderi et al.[15] reported that the epithelial healing period was shorter in the Trans-PRK than in the PRK. It could be owing to the difference in epithelial denuding area and ablation area between the two groups; in Trans-PRK, the epithelial removal size is equal to the ablation size, whereas in the conventional PRK, the epithelial removal size is more than the ablation size, which could defer re-epithelialization[16].

The temporary chemical toxicity of alcohol to the limbal stem cells and/or to the residual epithelial cells might be responsible for the increased pain and the slower healing time in the PRK. The stromal bed was also more uniform with no epithelial islands centrally, and there was a smoother peripheral progression in the Trans-PRK group than in the PRK group[5].

In the present study, we found the incidence of haze was significantly lower in the Trans-PRK group, which agrees with Fadlallah et al.[5].

A lower incidence of postoperative corneal haze was detected in the Trans-PRK group compared with the AA-PRK group in the study of Bakhsh et al.[11], at all-time tested points 1 week, 1 month, and 3 months with statistically significant differences possibly due to less keratocytes loss and apoptosis, no alcohol-induced toxicity, less epithelial injury (nontouch technique), and hence less haze formation in the Trans-PRK group. This finding is similar to that of Helena et al.[17], in which they reported quantitative and qualitative differences in keratocytes apoptosis among LASIK, epithelial scrape-PRK, and Trans-PRK, and similar to that of Celik et al.[12], but in contrary to an old study by Møller-Pedersen et al.[18], in which they reported increased keratocytes activation, intense inflammatory response, and myofibroblast transformation in Trans-PRK. However, during the follow-up, corneal haze intensity had a tendency to decrease until reaching to postoperative 6 months, where there was no haze detected.

In agreement with our findings, the study of Wang et al.[9] reported that haze never exceeded the score of 2 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.[19], with slightly higher score of haze (score 3).

The Trans-PRK group in our study had a better visual acuity after week, 1 month, and 3 months after surgery and refractive results at first month and third month postoperatively. In the Trans-PRK group, 3-month postoperation result showed a higher statistically significant association of UCVA within ±1 line of the preoperative BCVA (P < 0.001), and there was no statistical significant difference (P = 0.433) in the PRK group. Despite this no significant difference in PRK group, the visual outcome was satisfactory in this group.

In disagreement with our study, the study of Kaluzny et al.[10] provides very similar results between single-step Trans-PRK and conventional PRK 3 months postoperatively in terms of UDVA, CDVA, and Manifest Refraction Spherical Equivalent (MRSE). The correlation between attempted versus achieved MRSE was very high in both groups, with no statistically significant difference between the two groups.

Fadlallah et al.[5] reported that at 1 week, the UDVA was statistically significantly better in the control group than the Trans-PRK group, which agrees with our results; however, at 3 months, there was no statistically significant difference in UDVA, corrected distance visual acuity, or manifest refraction between the groups, which was not consistent with our study.

Our findings are supported by the study of Ghobashy et al.[8] only during the early postoperative period, as the results of this study showed the UCVA was significantly better in group Trans-PRK 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 in comparison with the PRK group.

Our findings are in contrast to the study of Bakhsh et al.[11]. Regarding the primary outcomes of visual results, there were no statistically significant differences between the two groups regarding the mean of postoperative MRSE at all-time tested points, as well as no significant differences at 3 and 6 months in postoperative mean UDVA, BCVA, and safety index. However, there were statistically significant differences in the early postoperative period at day 1, week 1, and month 1 in UDVA and in the efficacy index at day 1 and week 1 for the Trans-PRK group, as patients' eyes recovered faster and inconsistently at the same time in contrast to those of the AA-PRK group, where some eyes improved fast whereas others took 2–3 months; those who did not experience a fast improvement were told that they will eventually get better with visual stability after 3 months.

Lee et al.[14] reported the clinical and visual results after PRK using three epithelial removal techniques (mechanical, alcohol-assisted, and excimer laser-assisted) and found no marked difference among the three groups, as in our study. Ghadhfan et al.[20] compared the refractive outcomes and complications of LASIK, Trans-PRK, traditional PRK, and LASEK. They detected slightly better visual results after trans-PRK than after LASEK and the others, but mitomycin-C application was higher in Trans-PRK-treated eyes.

Naderi et al.[15] reported that Trans-PRK seemed to be superior to conventional PRK for treatment of low to moderate myopia in terms of postoperative pain, epithelial healing time, visual recovery, and safety and efficacy indices. They reported UDVA at 6-month postoperative of 0.002 ± 0.03 and 0.003 ± 0.04 on log MAR chart (P = 0.09) in each group, respectively[2].

On the contrary, the earlier techniques for epithelium removal utilizing excimer laser in phototherapeutic keratectomy mode did not show much advantage over conventional PRK, as reported in a retrospective study that compared three methods of epithelial removal [mechanical, alcohol-assisted, and Trans-PRK (in phototherapeutic keratectomy mode)] and showed significant differences in both the visual outcomes and the refractive results of the three epithelial removal techniques, with the long-term outcomes being best for alcohol-assisted PRK. This study showed that between 1 and 6 months postoperatively, a manifest correction within ±0.50 D of the attempted correction was achieved by a significantly higher proportion of eyes in the alcohol-assisted PRK group than in the other two groups (P < 0.001). When examined more than 1-year postoperatively, less than half of eyes in the Trans-PRK group achieved manifest correction within ±0.50 D of the attempted correction. This was a significantly smaller proportion compared with the other two groups (P < 0.0001)[21].

  Conclusion Top

This study highlighted the advantages of Trans-PRK technique over conventional PRK. Trans-PRK seems to be a safe and effective technique for treatment of mild to moderate myopia with or without astigmatism. However, during the 3 months after surgery, there were significant differences in UDVA, level of haze, and complete corneal epithelial healing time, in which level of haze was less and healing time were shorter in the Trans-PRK group, which resulted in patients viewing it as a friendly procedure and providing higher patient comfort.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Seiler T, Holschbach A, Derse M, Jean B, Genth U. Complications of myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1994; 101:153–160.  Back to cited text no. 1
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Naderi, M, Jadidi K, Mosavi SA, Daneshi S. Transepithelial photorefractive keratectomy for low to moderate myopia in comparison with conventional photorefractive keratectomy. J Ophth Vision Res 2016; 11:358.  Back to cited text no. 15
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Møller-Pedersen T, Cavanagh HD, Petroll WM, Jester JV. Corneal haze development after PRK is regulated by volume of stromal tissue removal. Cornea 1998; 17:627–639.  Back to cited text no. 18
Hashemi H, Taheri SMR, Fotouhi A, Kheiltash A. Evaluation of the prophylactic use of mitomycin-C to inhibit haze formation after photorefractive keratectomy in high myopia: a prospective clinical study. BMC Ophthalmol 2004; 4:12.  Back to cited text no. 19
Ghadhfan F, Al-Rajhi A, Wagoner MD. Laser in situ keratomileusis versus surface ablation: visual outcomes and complications. J Cataract Refract Surg 2007; 33:2041–2048.  Back to cited text no. 20
Shapira, Y, Mimouni, M, Levartovsky, S, Varssano, D, Sela, T, Munzer, G, Kaiserman, I. Comparison of three epithelial removal techniques in PRK: mechanical, alcohol-assisted, and trans-epithelial laser. J Refract Surg 2015; 31:760–766.  Back to cited text no. 21


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3], [Table 4]


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