Effect of intraoperative mitomycin-C on healthy corneal endothelium after laser-assisted subepithelial keratectomy

The Long Noncoding RNA LINC00963 Inhibits Corneal Fibrosis Scar Formation by Targeting miR-143-3p

Corneal fibrosis is a complication of severe corneal injury, one of the major causes of vision loss. The formation of myofibroblasts has emerged as a key stimulative factor of corneal fibrosis. In the current study, we focused on the role of LINC00963 in regulating corneal fibrosis. Transforming growth factor β1 (TGF-β1) was used to induce human corneal stromal cells differentiating into corneal myofibroblasts, and the significant increase of α-smooth muscle actin (α-SMA) was verified by quantitative real-time PCR (qRT-PCR), western blot, and immunofluorescence, respectively. LINC00963 was identified to be one-half decreased compared with nonstimulated human corneal stromal cells, indicating that it might play a role in corneal fibrosis. Interestingly, overexpression of LINC00963 resulted in decreased formation of myofibroblasts indicating that it might exhibit an inhibiting effect. Moreover, bioinformatics tool was applied to predict the downstream target of LINC00963. We investigated that LINC00963 suppressed α-SMA induced by TGF-β1 in corneal fibroblasts, at least in part, by downregulating the expression of miR-143-3p. In addition, either LINC00963 promotion or miR-143-3p inhibition could significantly decrease myofibroblast contractility and collagen I and III secretion, which are the key to contribute to corneal fibrosis. Taken together, our study identified LINC00963 as a promising therapeutic target.

A Prospective Evaluation of the Effect of Mitomycin-C on Corneal Endothelium after Photorefractive Keratectomy for Myopia Correction

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.

Non-contact specular microscopy with Topcon instruments to assess central corneal thickness of healthy human eyes - A 20 year review

BACKGROUND

The purpose of this review was to evaluate the consistency of central corneal thickness (CCT) values reported with use of Topcon SP-2000 P and SP-3000 P non-contact specular microscopes since their introduction in 1999 with the two microscopes having been commonly used in a wide range of studies.

METHODS

As a primary resource, PubMed was used to search for peer-reviewed articles in any language that included CCT values obtained with non-contact specular microscopy reported for humans with nominally healthy corneas. Relevant articles were obtained and any cited publications also checked.

RESULTS

A total of 76 articles were identified which reported CCT on different small-to-moderate sized groups of individuals, published between 1999 and 2019. From these, an overall group mean CCT value of 0.525 ± 0.013 mm (median 0.525 mm) can be calculated. An estimated 95 % confidence interval (CI, based on 1.96 SD) would be between 0.500 and 0.550 mm. For the two Topcon models, the group mean ± SD values were 0.529 ± 0.013 mm and 0.517 ± 010 mm respectively. An assessment of the CCT data sets in relation to the reported average age indicated no statistically significant effect (p = 0.289, r = -0.129). Very similar average CCT values were also encountered in 4 other reports where these microscopes were used in large-scale population studies as well as in 2 other reports using the newer Topcon SP-1 P model.

CONCLUSIONS

The Topcon stand-alone non-contact specular microscopes have yielded consistent and predictable corneal thickness measures over many years.

Biological effects of mitomycin C on late corneal haze stromal fibrosis following PRK

This review details the current understanding of the mechanism of action and corneal effects of mitomycin C (MMC) for prophylactic prevention of stromal fibrosis after photorefractive keratectomy (PRK), and includes discussion of available information on dosage and exposure time recommended for MMC during PRK. MMC is an alkylating agent, with DNA-crosslinking activity, that inhibits DNA replication and cellular proliferation. It acts as a pro-drug and requires reduction in the tissue to be converted to an active agent capable of DNA alkylation. Although MMC augments the early keratocyte apoptosis wave in the anterior corneal stroma, its most important effect responsible for inhibition of fibrosis in surface ablation procedures such as PRK is via the inhibition of mitosis of myofibroblast precursor cells during the first few weeks after PRK. MMC use is especially useful when treating eyes with higher levels of myopia (≥approximately 6 D), which have shown higher risk of developing fibrosis (also clinically termed late haze). Studies have supported the use of MMC at a concentration of 0.02%, rather than lower doses (such as 0.01% or 0.002%), for optimal reduction of fibrosis after PRK. Exposure times for 0.02% MMC longer than 40 s may be beneficial for moderate to high myopia (≥6D), but shorter exposures times appear to be equally effective for lower levels of myopia. Although MMC treatment may also be beneficial in preventing fibrosis after PRK treatments for hyperopia and astigmatism, more studies are needed. Thus, despite the clinical use of MMC after PRK for nearly twenty years-with limited evidence of harmful effects in the cornea-many decades of experience will be needed to exclude late long-term effects that could be noted after MMC treatment.

EpiLASIK with Mitomycin C

Purpose

Mitomycin C after photorefractive keratectomy (PRK) is used to reduce the development of haze and regression in higher intended corrections. The aim of this study was to investigate the safety, stability, and efficacy of EpiLASIK with mitomycin C.

Methods

Fifty eyes of 29 patients underwent EpiLASIK with the Gebauer EpiLift microkeratome. The mean preoperative spherical equivalent was −6.89 D (SD ±0.63, range −6.0 to −8.0 D). After the laser ablation, mitomycin C 0.02% was applied for 30 seconds on a sterile filter paper. Preoperatively and 1, 3, 6, and 12 months after surgery, a full ophthalmic examination was performed.

Results

In 42 of 50 eyes, the bandage contact lens was removed at day 3. Twelve months after surgery, 96% of all eyes were within ±1.0 D and 82% were within ±0.5 D of intended correction. Five percent of all patients lost 1 line of best-corrected Snellen visual acuity, 42% were stable, and 56% gained 1 or more lines. In most patients, the cornea was clear during the whole follow-up, and in 10% only trace haze was visible. The uncorrected visual acuity was at least 1.0 in 86% of all patients, and all patients reached 0.5.

Conclusions

EpiLASIK with mitomycin C with higher intended corrections seems to be an effective and safe procedure. With the application of mitomycin C, only minimal haze appears.

Endothelial cell changes after photorefractive keratectomy with graded usage of mitomycin C

PURPOSE

To compare differences in the endothelial cells before and after photorefractive keratectomy (PRK) for myopia with refractive error graded mitomycin C (MMC) application.

METHODS

In a prospective randomized clinical trial, forty-eight myopic patients referred to Khatam-al-Anbia Eye Hospital, Mashhad, Iran, for PRK. Patients were treated with PRK by a Bausch and Lomb Technolas 217z excimer laser (Bausch and Lomb, Rochester, NY). MMC was applied after PRK 5 s for each diopter of spherical equivalent myopic refractive error corrected. The manifest refraction, visual acuity, MMC treatment length, corneal pachymetry and specular microscopy were evaluated preoperatively and at 1 and 6 months postoperatively.

RESULTS

A total of 48 cases (96 eyes, 68.75% female) were treated, with a mean age of 26.70 ± 4.89 years (range, 18-34 years). Postoperative cell density, cell size and polymegathism did not significantly change. On the other hand, standard deviation (SD) of cell size (P = 0.008), pleomorphism (P = 0.003) and coefficient of variation (CV) (P = 0.016) were significantly increased. None of these parameters was related to the length of MMC application. Corneal thickness decreased significantly after the operation but it increased 6 months postoperatively compared with the first month (P < 0.001).

CONCLUSION

MMC application for PRK in myopia can affect the endothelial cells, but in early follow-ups, it does not affect the cell density or size. Cell size was changed but it was obvious not in mean cell size, but in SD and CV. MMC time below the 30 s was not significant on endothelial cell changes.

Preparation and Thickness Profile of Endothelial Keratoplasty Lenticules from Donated Whole Eyes with Previous Photorefractive Keratectomy

Purpose:

To describe the preparation and thickness profiles of endothelial keratoplasty lenticules harvested from eyes with previous photorefractive keratectomy (PRK).

Methods:

Donor whole eyes that underwent PRK were subjected to microkeratome-assisted dissection for Descemet stripping automated endothelial keratoplasty. Specular microscopy and Visante optical coherence tomography were performed on precut corneas. Endothelial cell indices and thickness profiles of endothelial keratoplasty lenticules were statistically analyzed. Postoperative reports for transplanted lenticules were recorded.

Results:

Over a 6-month period, 2,929 whole eyes from 1,471 donors were screened for PRK. Twenty-five (0.85%) eyes from 14 donors were diagnosed with disciform haziness due to prior PRK and were used uneventfully for preparation of endothelial keratoplasty lenticules. Mean endothelial cell count was 3164.6 ± 311.0/mm² and mean central posterior lenticule thickness was 128 ± 34 μm. Posterior lenticules revealed an increase in thickness from the central to peripheral cornea (mean increase of 26.2 μm at pericentral and 90.4 μm at peripheral locations). Mean increase in thickness was statistically different between two peripheral locations (74.5 μm vs. 108.1 μm, P = 0.047). Postoperative reports of transplanted lenticules revealed no posterior flap detachment or loss of clarity at least three months after the surgery.

Conclusion:

PRK donor whole eyes are potential sources for preparation of microkeratome-assisted thin endothelial keratoplasty lenticules with a high endothelial cell count. Although an asymmetric and significant increase in thickness was present at the peripheral cornea, neither attachment nor clarity of transplanted lenticules was affected by variations in thickness of precut corneas.

Mitomycin-C in corneal surface excimer laser ablation techniques: a report by the American Academy of Ophthalmology

OBJECTIVE

To review the published literature assessing the efficacy and safety of mitomycin-C (MMC) as an adjunctive treatment in corneal surface excimer laser ablation procedures.

METHODS

Literature searches of the PubMed and Cochrane Library databases were last conducted on August 19, 2014, without language or date limitations. The searches retrieved a total of 239 references. Of these, members of the Ophthalmic Technology Assessment Committee Refractive Management/Intervention Panel selected 26 articles that were considered to be of high or medium clinical relevance, and the panel methodologist rated each article according to the strength of evidence. Ten studies were rated as level I evidence, 5 studies were rated as level II evidence, and the remaining 11 studies were rated as level III evidence.

RESULTS

The majority of the articles surveyed in this report support the role of MMC as an adjunctive treatment in surface ablation procedures. When MMC is applied in the appropriate concentration and confined to the central cornea, the incidence of post-surface ablation haze is decreased. Although a minority of studies that evaluated endothelial cell density (ECD) reported an MMC-related decrease in ECD, no clinical adverse outcomes were reported.

CONCLUSIONS

Over the past 15 years, the use of MMC during surgery in surface ablation has become widespread. There is good evidence of the effectiveness of MMC when used intraoperatively as prophylaxis against haze in higher myopic ablations. Although there are reports of decreased endothelial counts after the administration of MMC during surgery, the clinical significance of this finding remains uncertain, because no adverse outcomes were reported with as much as 5 years of follow-up. Optimal dosage, effectiveness as prophylaxis in lower myopic and hyperopic ablations, and long-term safety, particularly in eyes with reduced corneal endothelial cell counts from prior intraocular surgery, have yet to be established.

Visual and subjective outcomes of phototherapeutic keratectomy after Descemet's stripping endothelial keratoplasty

Background

Patients with endothelial disease also often have scarring or surface corneal disease. This study examined the outcomes of phototherapeutic keratectomy (PTK) performed in patients with prior Descemet’s stripping endothelial keratoplasty (DSEK).

Methods

This retrospective case series examined all patients undergoing PTK after DSEK in a single private practice. The primary outcome was best-corrected visual acuity, with secondary outcomes of change in spherical equivalent versus targeted change, change in endothelial cell count, improvement in corneal topography, and subjective satisfaction with vision.

Results

For the ten patients who met the inclusion criteria, mean best-corrected visual acuity improved from logarithm of the minimum angle of resolution (logMAR) 0.43 to 0.36 (P=0.24) at the most recent postoperative visit. PTK treatments that included a refractive component showed good predictability of 1.13 diopters spherical equivalent/diopter attempted. There was no evidence of a decrease in endothelial cell count from PTK, even with the use of mitomycin C (P=0.95). Subjectively, 80% of patients noted improvement in their vision.

Conclusion

PTK after DSEK has the potential to improve patients’ vision with high levels of patient satisfaction, even though many patients had significant ocular comorbidities. Surgeons should consider using PTK to treat anterior corneal pathology following DSEK.

Application of umbilical cord serum eyedrops after laser epithelial keratomileusis

PURPOSE

To investigate the efficacy of umbilical cord serum eyedrops after laser epithelial keratomileusis (LASEK).

METHODS

Sixty patients (120 eyes) with myopia who underwent LASEK were studied. Thirty-two patients (64 eyes) were treated with 20% umbilical cord serum eyedrops in combination with conventional treatment (group A), and 28 patients (56 eyes) received conventional treatment only (group B). Epithelial healing time was analysed. Visual acuity, refraction, haze score (0-4) and tear film and ocular surface parameters were evaluated at 1, 2, 4 and 12 weeks after LASEK. The concentration of transforming growth factor (TGF)-β1 in tears was measured with ELISA at 1 week after LASEK.

RESULTS

No significant differences in visual acuity and refraction were found between groups. The mean time to epithelial healing was 3.53 ± 1.19 days in group A and 3.91 ± 1.41 days in group B (p = 0.18). The mean haze scores at 2 and 4 weeks were 0.59 ± 0.80 and 0.31 ± 0.54 in group A and 1.06 ± 0.91 (p = 0.02) and 0.69 ± 0.78 (p = 0.03) in group B. Four and 12 weeks after LASEK, tear film break-up time was longer and keratoepitheliopathy score was lower in group A compared with group B. The mean concentration of TGF-β1 was lower in group A compared with group B (p = 0.01).

CONCLUSION

Application of 20% umbilical cord serum eyedrops in addition to conventional treatment after LASEK can reduce early postoperative corneal haze and improve tear film and ocular surface parameters.

Corneal endothelium after refractive surgery

The endothelium is vital to the health and optical clarity of the human cornea. The safety of procedures to correct refractive errors depends on preservation of an intact corneal endothelium. Disease states and genetic and environmental factors affect the corneal endothelium; an unstable corneal endothelium can impact the success of refractive surgery. Technological advances and recent laboratory findings have improved the ability to assess the endothelium. The status of the corneal endothelium after laser in situ keratomileusis, photorefractive keratectomy, phakic intraocular lenses, and adjuvants to these treatments has been the topic of numerous clinical trials. Safety guidelines for refractive surgery procedures should be followed to minimize deleterious effects on the corneal endothelium.

FINANCIAL DISCLOSURE

Neither author has a financial or proprietary interest in any material or method mentioned.

Efficacy of surface ablation retreatments using mitomycin C

PURPOSE

To evaluate the visual and refractive results and the incidence of complications after laser subepithelial keratectomy (LASEK) enhancement using mitomycin C (MMC) after a previous LASEK procedure with MMC.

DESIGN

Retrospective, noncomparative, interventional case series.

METHODS

Setting was Vissum Santa Hortensia, Madrid, Spain. We performed a retrospective study of LASEK-treated eyes that received intraoperative MMC for 30 seconds and that needed an enhancement procedure. LASEK retreatment with MMC 0.02%, applied for 60 seconds, was performed 3 to 6 months after the initial surgery. We measured the visual and refractive results 3 months after the enhancement and the incidence of complications.

RESULTS

Eighty-two eyes were included in the study. The preoperative data were best spectacle-corrected visual acuity (BSCVA) 1.08 +/- 0.19, sphere -4.68 +/- 2.8 diopters (D), and cylinder -1.30 +/- 1.20 D. Three to 6 months postoperatively, before enhancement, the uncorrected VA (UCVA) was 0.59 +/- 0.2; the BSCVA, 0.976 +/- 0.2; the residual sphere, +0.17 +/- 0.7 D, and the cylinder, -0.39 +/- 0.5 D. Three months after retreatment, the UCVA was 0.93 +/- 0.1; the BSCVA, 0.977 +/- 0.1; the residual sphere, 0.09 +/- 0.3 D; and the residual cylinder, -0.2 +/- 0.3 D. The safety index after retreatment was 1.01 +/- 0.1, and the efficacy index was 0.96 +/- 0.1. No haze, no delay in epithelial healing, and no case of endothelial decompensation were detected.

CONCLUSION

Surface ablation retreatment using MMC seems to be effective to correct residual refractive errors after an initial surgery with MMC.

Mitomycin C in corneal refractive surgery

Mitomycin C has played a deciding role in the current revival of excimer laser surface ablation techniques. We review the literature regarding mechanism of action of mitomycin C, histological effects on the cornea, and indications, dose, exposure time, and toxicity of mitomycin C in corneal refractive surgery. Mitomycin C is an alkylating agent with cytotoxic and antiproliferative effects that reduces the myofibroblast repopulation after laser surface ablation and, therefore, reduces the risk of postoperative corneal haze. It is used prophylactically to avoid haze after primary surface ablation and therapeutically to treat pre-existing haze. There is no definite evidence that establishes an exact diopter limit or ablation depth at which to apply prophylactic mitomycin C. It is usually applied at a concentration of 0.2mg/ml (0.02%) for 12 to 120 seconds over the ablated stroma, although some studies suggest that lower concentrations (0.01%, 0.002%) could also be effective in preventing haze when treating low to moderate myopia. This dose of mitomycin C has not been associated with any clinically relevant epithelial corneal toxicity. Its effect on the endothelium is more controversial: two studies report a decrease in endothelial cell density, but the majority of reports suggest that the endothelium is not altered. Regarding mitomycin C's effect on keratocyte population, although animal studies report keratocyte depletion after its use, longer follow-up suggested that the initial keratocyte depletion does not persist over time.