|Year : 2021 | Volume
| Issue : 2 | Page : 111-115
A prospective evaluation of the effect of mitomycin-c on corneal endothelium after photorefractive keratectomy for myopia correction
Sashwanthi Mohan1, Pratik Gogri2, Somasheila I Murthy1, Sunita Chaurasia1, Ashik Mohamed3, Pankaj Dongre2
1 Department of Cornea, The Cornea Institute, Hyderabad, Telangana, India
2 Department of Cataract and Refractive Surgery, L V Prasad Eye Institute, Hyderabad, Telangana, India
3 Ophthalmic Biophysics, L V Prasad Eye Institute, Hyderabad, Telangana, India
|Date of Submission||14-Nov-2020|
|Date of Acceptance||23-Jun-2021|
|Date of Web Publication||25-Sep-2021|
Dr. Somasheila I Murthy
The Cornea Institute, LV Prasad Eye Institute, Kallam Anji Reddy Campus, LV Prasad Marg, Banjara Hills, Hyderabad - 500 034, Telangana
Source of Support: None, Conflict of Interest: None
| Abstract|| |
PURPOSE: The aim of the study was to assess the effect of mitomycin-C (MMC) 0.02% application on corneal endothelium in patients undergoing photorefractive keratectomy (PRK) for the correction of myopia and compound myopic astigmatism.
METHODS: A prospective observational study including patients with myopia who underwent PRK plus intraoperative application of MMC 0.02%. All patients underwent noncontact specular microscopy preoperatively and 6 months postoperatively. The following parameters were analyzed: mean cell area (MCA), central corneal endothelial cell density (ECD), and coefficient of variation (CV) in cell size.
RESULTS: One hundred and thirty-nine eyes of 73 patients with a mean age of 24.95 ± 3.23 years were included in the study. Mean baseline preoperative pachymetry was 519.54 ± 28.62 μm. The mean preoperative spherical equivalent was −4.6 ± 2.3D (range from −1D to −10D) which decreased to mean postoperative spherical equivalent of −0.125 ± 0.32D. Mean baseline ECD was 2829.3 ± 188.8 cells/mm2, MCA was 354.6 ± 24.9 μm2/cell, CV was 0.35 ± 0.06, and hexagonality was 50.1 ± 6.64. The mean ECD decreased by 43 ± 1.6 cells/mm2 which was not statistically significant (P = 0.07). The MCA increased by 5 ± 1.3 μm2/cell, but this was not statistically significant (P = 0.07). However, both the CV and percentage of hexagonal cells showed statistically significant differences in the median values as compared to preoperatively (P < 0.001).
CONCLUSION: In our study, MMC had no significant effect on corneal endothelial cell counts or MCA. While there were statistically reduced CV and percentage of hexagonal cells, these did not appear to be clinically significant. MMC is safe to use routinely to prevent haze formation in PRK.
Keywords: Corneal endothelium, endothelial cell counts, high myopia, mitomycin-C, photorefractive keratectomy
|How to cite this article:|
Mohan S, Gogri P, Murthy SI, Chaurasia S, Mohamed A, Dongre P. A prospective evaluation of the effect of mitomycin-c on corneal endothelium after photorefractive keratectomy for myopia correction. Middle East Afr J Ophthalmol 2021;28:111-5
|How to cite this URL:|
Mohan S, Gogri P, Murthy SI, Chaurasia S, Mohamed A, Dongre P. A prospective evaluation of the effect of mitomycin-c on corneal endothelium after photorefractive keratectomy for myopia correction. Middle East Afr J Ophthalmol [serial online] 2021 [cited 2022 Jun 25];28:111-5. Available from: http://www.meajo.org/text.asp?2021/28/2/111/326670
| Introduction|| |
Cornea-based laser refractive eye surgery is currently the leading method of improving uncorrected visual acuity (UCVA) and reducing the dependence on glasses and contact lenses. The use of excimer laser for the correction of myopia was approved by the Food and Drug Administration in 1995. Initially, surface ablation with the help of excimer laser, known as photorefractive keratectomy (PRK), was performed. Subsequently, laser-assisted in situ keratomileusis (LASIK) has become the most performed keratorefractive laser procedure. The use of mitomycin-C (MMC) to prevent corneal haze formation has led to a resurgence of PRK for surgical treatment of myopia.
MMC is a noncell cycle-specific antimetabolite. It has antiproliferative effect on cells having a high mitosis rate. It acts by inhibiting synthesis of DNA and interference in transcription of RNA and protein synthesis. Haze formation after PRK is attributed to subepithelial fibrosis due to abnormal activation or proliferation of stromal keratocytes following laser ablation. MMC has inhibitory effects on keratocyte proliferation and causes keratocyte apoptosis, thus preventing haze formation.
MMC targets mainly actively proliferating cells and inhibits their proliferation. Thus, the corneal endothelium should be less vulnerable to MMC effects because it is not an actively dividing tissue. However, laboratory evidence of MMC detected in the aqueous humor has led to a concern about endothelial toxicity.,,
The effect of a single intraoperative dose of MMC during refractive surgery on the corneal endothelium has been studied before, but the results have been quite varying. Endothelial toxicity by MMC has been reported in a few studies, whereas others have reported no significant change in corneal endothelial density or morphology with follow-up.,, In this study, we assess the changes in endothelial cell morphology and density in mild-to-high myopes undergoing PRK with MMC application.
| Methods|| |
The Institutional Ethics Committee approved the study (Ethics Ref. No. LEC 06-16-061), and an informed consent was taken from all the participants of the study. This prospective observational study included patients with mild-to-high myopia (spherical equivalent, −0.50 D–−10.00 D). Sixty-six patients underwent procedure in both eyes, whereas seven patients underwent in one eye only. Patients with unstable refraction, keratoconus, corneal scarring, pellucid marginal degeneration, corneal dystrophy or degeneration, herpetic keratitis, lens opacities, retinal pathology, glaucoma suspect, and dry eyes were excluded from the study. Furthermore, the patients with medical contraindications such as diabetes mellitus, autoimmune diseases, immunocompromised status and pregnancy, or lactation were excluded from the study.
Preoperative evaluation included detailed history taking, measurement of UCVA, and best-corrected visual acuity (BCVA) using a Snellen chart, undilated manifest refraction, subjective acceptance, slit-lamp examination, intraocular pressure (IOP) measurement by Goldmann's applanation tonometer, dilated fundus examination, and corneal topography with pachymetry (WaveLight Pentacam Oculyzer, Alcon Inc., Fort Worth, Texas). Corneal endothelial imaging was performed by a trained optometrist using specular microscopy (Specular Microscope EM-3000, Tomey Corporation, Nagoya, Japan). The instrument analyzed information on various qualitative and quantitative parameters in a single scan, namely, number of cells, endothelial cell density (ECD), average cell area, standard deviation (SD) of cell area, coefficient of variation (CV) of cell area, maximum, minimum, and mean cell area (MCA). The specular microscopy was performed in the automatic mode. The best image was used for analysis of quantitative parameters.
All participants were operated by three experienced surgeons who followed the same operating technique, using an 193 nm excimer laser machine (Wavelight EX500, Alcon Laboratories, Fort Worth, TX, USA). Topical 0.5% proparacaine hydrochloride was used to anesthetize the cornea. Preoperative skin prep was done, and a sterile surgical drape along with an eyelid speculum was positioned. The epithelial adhesions were loosened with the help of 0.5% proparacaine hydrochloride placed for 30 s, and the epithelium was then mechanically debrided in the central 8 mm of cornea with the help of a hockey stick instrument. Thereafter, ablation was performed using the excimer laser. An optic zone of 6–6.5 mm was kept in all cases. Intraoperatively, pachymetry was assessed before the start of surgery and after laser ablation to calculate the residual stromal bed thickness. Subsequently, a disc prepared with a merocel surgical sponge, 7 mm in diameter, and soaked with MMC 0.02% (0.2 mg/ml, diluted in balanced salt solution [BSS]), was applied over the ablated surface for a duration depending on the refractive power (D) required (10 s for every 1.00 D). A thorough saline wash is given with 30 ml of BSS following which a bandage contact lens (BCLs) was applied (Acuvue Oasys, FL, USA).
Postoperatively, all participants were instructed to use 0.5% moxifloxacin hydrochloride eye drops four times a day for 1 week and nepafenac 0.1% for the first 3–5 days until healing of epithelium. Thereafter, BCL was removed, and patients were started on loteprednol etabonate 0.5% eye drops four times a day and tapered every week thereafter. Furthermore, topical tear substitute eye drop was prescribed four times a day for 3 months. Follow-up examinations were scheduled 1, 3, 7, and 30 days, 3 months, and 6 months postoperatively. At each examination except on days 1 and 3, UCVA, BCVA, manifest refraction, and IOP were checked. Specular microscopy was repeated 6 months after the surgery.
Statistical analysis was done using Origin v7.0 software (OriginLab Corporation, Northampton, MA, USA). Visual acuity measured using Snellen's visual acuity chart was converted to logMAR values. Continuous data were checked for the normality of distribution by Shapiro–Wilk test. Data were presented as median with interquartile range (IQR) for nonparametric data and mean ± SD for parametric data. Equality of variance was assessed by Levene test. For parametric data with equal variance, paired t-test was used to compare preoperative and postoperative parameters. For nonparametric data and parametric data with unequal variance, Wilcoxon signed-rank test was used. Spearman correlation was used to evaluate the relationship between MMC duration of residual stromal bed thickness with changes in postoperative ECD, MCA, CV%, and %6A. A P < 0.05 was considered statistically significant.
| Results|| |
This study included 139 eyes of 73 patients (51 males and 22 females). Median age at surgery was 24.8 years (IQR, 23.2–27 years). The baseline characteristics of the study sample are highlighted in [Table 1]. Sixty-six patients underwent procedure in both eyes, whereas seven patients underwent in one eye only. Median preoperative spherical equivalent was −4.00 (IQR, −2.25 D–−6.00 D). Median preoperative BCVA was 0.00 (IQR, 0.00–0.00) and median BCVA was 0.00 (IQR, 0.00–0.00) at 6-month follow-up. No statistically significant difference was noted between preoperative BCVA and postoperative 6 months BCVA (P = 0.87). This shows that the UCVA after surgery was comparable to the BCVA before surgery.
The comparative analysis of the preoperative and postoperative specular microscopy characteristics of the patients is shown in [Table 2]. There was no statistically significant difference between the preoperative and postoperative ECD and MCA. At 6 months, the increase in median CV from preoperative values was found to be statistically significant (P = 0.0003) signifying increase in polymegathism. At 6 months, the percentage of hexagonal cells decreased by a mean of 2.26% ±0.34%. This was found to be statistically significant (P < 0.0001). This signifies pleomorphism.
There was no relationship between MMC duration (median 45 s [IQR, 30–60 s]) and change in ECD (P = 0.27), MCA (P = 0.24), CV (P = 0.26), and percentage of hexagonal cells (P = 0.38). Similarly, there was no correlation between residual stromal bed thickness and change in ECD (P = 0.42), MCA (P = 0.39), CV (P = 0.06), and percentage of hexagonal cells (P = 0.76).
None of the patients included in the study developed postoperative complications such as persistent epithelial defects, infectious keratitis, steroid response, postoperative dry eye, or significant haze formation. None of the patients had a loss of BCVA 6 months after the surgery.
| Discussion|| |
This study was performed to evaluate the corneal endothelial toxicity (if any) of MMC used intraoperatively during PRK surgery. Using specular microscopy, we studied the changes in quantitative (ECD) and qualitative (CV, MCA, and percentage of hexagonal cells) parameters. At 6 months, there was no significant change in endothelial cell count from preoperative to postoperative values. A few previous studies have looked at the ECD after PRK without the usage of MMC, and the results were similar to that obtained in the present study.,,
In 2005, Lee et al. conducted a retrospective noncomparative case series which included 536 patients (1011 eyes) who had had PRK with intraoperative application of MMC 0.02% ranging from 30 s to 2 min. They concluded that there was no statistically significant difference in the postoperative ECD from preoperative measurements. In 2007, Goldsberry et al. studied 16 eyes with a planned ablation depth >75 μ of patients who underwent PRK with 12 s of 0.02% MMC application. They found out that MMC usage after PRK for the prevention of haze did not have any significant effect on endothelial cell morphology and density. Another prospective randomized clinical trial in 2007 by Diakonis et al. consisted of 15 patients, in which one eye of patient underwent PRK with MMC application and fellow eye was treated with Epi-LASIK. They found a reduction in the ECD until 3 months after surgery, however, it was not statistically significant.
In 2011, Zare et al. conducted a prospective case series, where patients with moderate myopia underwent PRK with the application of MMC 0.02% for 40 s. They concluded that 0.02% MMC application for 40 s after PRK in patients with moderate myopia had no significant effect on corneal endothelial cells up to a 6-month follow-up period.
There are studies in literature which have shown the association of MMC usage with significant endothelial cell loss. Morales et al. found a significant reduction in endothelial cell count at 1 month (14.7%) and 3 months (18.2%) after PRK with MMC. Nassiri et al. also found reduction in central ECD in eyes undergoing PRK. The usage of MMC in this study was for 10–50 s after PRK with ablation depth above 75 μ. They also reported that male sex and the duration of MMC exposure to be significantly associated with more endothelial cell loss. Although these studies do report delirious effect of MMC on corneal endothelial cells, still there has never been a report of corneal endothelial decompensation after PRK with MMC application till date.,,, There have been isolated case reports of corneal edema after usage of MMC for glaucoma surgery or PRK, but each one of them had some risk factors for the same such as chronic uveitis, raised intraocular pressure, previous cataract surgery, or complicated surgery.,,, Hence, the cause of corneal endothelial decompensation in these reports cannot be completely attributed to the usage of MMC only.
The concentration of MMC we used was 0.02% (0.2 mg/mL) which was similar to the other studies but the duration of MMC application depended on the degree of myopic refractive error. In most of the abovementioned studies, a fixed duration of MMC was used for all the degrees of myopia. In our study, similar to the recent study by Gharaee et al. where 5 s of MMC was used for every diopter of myopia, we also used a graded method of application of MMC that ranged between 10 s and 90 s depending on the degree of myopia. For each diopter of myopia, 10 s of MMC was applied. There was no significant correlation between the change in the endothelial cell counts and morphology irrespective of the duration of MMC used. The significant change in CV and percentage of hexagonal cells in our study did not have any correlation to the duration of MMC used. While both CV and percentage of hexagonality achieved statistical significance, the numerical values appear to be clinically insignificant. It would have been interesting to perform these tests again at the end of 1 year to note if these changes still persisted.
We also looked at the correlation between residual stromal bed thickness and the change in endothelial cell counts and morphology. Thinner residual stromal bed thickness would in theory allow deeper penetration of MMC exposing the endothelium to its deleterious effects. However, we noted no significant correlation between the change in the endothelial cell counts and morphology irrespective of the residual stromal bed thickness in our study. This is consistent with the study by Zhao et al. where the effect of MMC on corneal endothelial cells was studied after LASEK. There also reported no significant correlation between the change in endothelial indices and the residual stromal bed thickness. The significant change in CV and percentage of hexagonal cells in our study could not be correlated to the residual stromal bed thickness either.
Changes in CV (polymegathism) and percentage of hexagonal cells (pleomorphism) are sensitive indices of a response to endothelial cell injury. Hence, a limitation of our study seems to be follow-up duration limited to 6 months. A longer duration of follow-up beyond 6 months would have been ideal. We could not address this in the current study due to limited number of patients who followed up till 1 year after surgery. Furthermore, we have not compared our results with a cohort of patients who underwent PRK without the use of MMC. This was not possible as usage of postoperative MMC after PRK is a standard practice at our institute.
| Conclusion|| |
In summary, our study has emphasized that MMC has no significant effect on corneal endothelial cell counts and MCA and irrespective of duration of application and can be routinely used to prevent haze formation in PRK. As changes in CV (polymegathism) and percentage of hexagonal cells (pleomorphism) are also sensitive indices of endothelial cell injury, a longer duration of follow-up and repeating the test is warranted.
Financial support and sponsorship
All autors are supported by a grant from Hyderabad Eye Research Foundation, India.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]