Corneal Keratocyte Apoptosis Following Topical Intraoperative Mitomycin C in Rabbits

Update on Corneal Confocal Microscopy Imaging

In vivo corneal confocal microscopy (IVCM) is a non-invasive ophthalmic imaging technique that provides images of the cornea at the cellular level. Despite the uses in ocular surface pathologies, in the last decades IVCM has been used to provide more knowledge in refractive surgery wound healing, in neuropathies diagnosis, etc. The observation of the corneal cells, both normal and inflammatory, and the possibility of quantification of the corneal nerve density with manual or automated tools, makes IVCM have a significant potential to improve the diagnosis and prognosis in several systemic and corneal conditions.

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.

Mitomycin C modulates intracellular matrix metalloproteinase-9 expression and affects corneal fibroblast migration

Mitomycin C (MMC) is often used to prevent postoperative corneal haze and subconjunctival fibrosis in ocular surgery. It also affects the motility and viability of the residual ocular cells, including corneal stromal cells. Extracellular matrix metalloproteinase-9 (MMP-9) contributes to the promotion of cell movement in macrophage and cancer cells, but the intracellular role of MMP-9 remained unclear. Herein, we illustrated the novel role of intracellular MMP-9 in MMC-suppressed cell migration using isolated human corneal fibroblasts (HCFs). In HCFs, MMC enhanced intracellular MMP-9 at transcriptional and protein levels. Using co-immunoprecipitation analysis, we confirmed that MMC enhanced the association between intracellular MMP-9 and inactive FAK/paxillin (PXN) complexes, i.e. PXN without phospho-tyrosine 118 (pY118) and FAK without phospho-tyrosine 397 (pY397). To verify the role of intracellular MMP-9 in migration, its gene was directly isolated from HCFs and highly expressed in HCFs by a lentivirus-based pseudovirus system with encephalomyocarditis virus (EMCV)-driven enhanced green fluorescent protein (GFP) as the MMP-9-IG-versus IG-expressing cells. Compared with the IG-expressing cells, higher intracellular MMP-9 expression in the MMP-9-IG-expressing HCFs proliferated and migrated more slowly. Phosphorylation of FAK at Y397 and PXN at both Y31 and Y118 were significantly less in the MMP-9-IG-expressing HCFs. These suggested that MMC-upregulated intracellular MMP-9 clutched inactive FAK/PXN complexes at focal adhesion sites to form a new "inactive" trimer, prohibited FAK/PXN complexes phosphorylation and retarded corneal fibroblast migration.

A Critical Overview of the Biological Effects of Mitomycin C Application on the Cornea Following Refractive Surgery

During the last 2 decades, modifying the shape of the cornea by means of laser photoablation has emerged as a successful and popular treatment option for refractive errors. Corneal surface ablation techniques such as photorefractive keratectomy (PRK) and laser-assisted subepithelial keratomileusis (LASEK) offer good refractive results while having a minimal impact on corneal biomechanical stability. Past limitations of these techniques included the long-term regression of refractive outcome and a vigorous healing response that reduced corneal clarity in some patients (giving rise to what is clinically described as “haze”). Mitomycin C (MMC) was introduced as a healing modulator and applied on the corneal surface after refractive surgery to address these drawbacks. This article critically reviews the available evidence on the biological effects, safety, and clinical benefits of the off-label use of MMC in corneal refractive surgery.

The corneal fibrosis response to epithelial-stromal injury

The corneal wound healing response, including the development of stromal opacity in some eyes, is a process that often leads to scarring that occurs after injury, surgery or infection to the cornea. Immediately after epithelial and stromal injury, a complex sequence of processes contributes to wound repair and regeneration of normal corneal structure and function. In some corneas, however, often depending on the type and extent of injury, the response may also lead to the development of mature vimentin+ α-smooth muscle actin+ desmin+ myofibroblasts. Myofibroblasts are specialized fibroblastic cells generated in the cornea from keratocyte-derived or bone marrow-derived precursor cells. The disorganized extracellular matrix components secreted by myofibroblasts, in addition to decreased expression of corneal crystallins in these cells, are central biological processes that result in corneal stromal fibrosis associated with opacity or "haze". Several factors are associated with myofibroblast generation and haze development after PRK surgery in rabbits, a reproducible model of scarring, including the amount of tissue ablated, which may relate to the extent of keratocyte apoptosis in the early response to injury, irregularity of stromal surface after surgery, and changes in corneal stromal proteoglycans, but normal regeneration of the epithelial basement membrane (EBM) appears to be a critical factor determining whether a cornea heals with relative transparency or vision-limiting stromal opacity. Structural and functional abnormalities of the regenerated EBM facilitate prolonged entry of epithelium-derived growth factors such as transforming growth factor β (TGF-β) and platelet-derived growth factor (PDGF) into the stroma that both drive development of mature myofibroblasts from precursor cells and lead to persistence of the cells in the anterior stroma. A major discovery that has contributed to our understanding of haze development is that keratocytes and corneal fibroblasts produce critical EBM components, such as nidogen-1, nidogen-2 and perlecan, that are essential for complete regeneration of a normal EBM once laminin secreted by epithelial cells self-polymerizes into a nascent EBM. Mature myofibroblasts that become established in the anterior stroma are a barrier to keratocyte/corneal fibroblast contributions to the nascent EBM. These myofibroblasts, and the opacity they produce, often persist for months or years after the injury. Transparency is subsequently restored when the EBM is completely regenerated, myofibroblasts are deprived of TGFβ and undergo apoptosis, and the keratocytes re-occupy the anterior stroma and reabsorb disordered extracellular matrix. The aim of this review is to highlight factors involved in the generation of stromal haze and its subsequent removal.

Moxifloxacin modifies corneal fibroblast-to-myofibroblast differentiation

BACKGROUND AND PURPOSE

Fibroblast-to-myofibroblast differentiation is associated with scarring, an important issue in corneal surgery. Moxifloxacin (MOX), commonly applied to prevent post-operative infection, would benefit more if it modifies fibroblast-to-myofibroblast differentiation other than antimicrobial activity. Our purpose was to explore whether MOX has anti-fibrotic effect in human corneal fibroblasts (HCFs).

EXPERIMENTAL APPROACH

HCFs were incubated in MOX-containing medium concurrently with TGF-β1 (co-treatment), before (pretreatment) or after (post-treatment) adding TGF-β1. HCF contractility was evaluated with a type I collagen gel contraction assay. Expression of α-smooth muscle actin (α-SMA), Smad2, phospho-Smad2-Ser467, Smad4 and Smad7 was determined by immunoblotting. Formation of α-SMA-positive filaments and distribution of active Smad2 were observed under confocal microscopy. Expression of TGF-β receptor types I (TGFBR1) and II (TGFBR2) was assessed with flow cytometry.

KEY RESULTS

MOX did not affect gel contractility or α-SMA filament formation in HCFs without TGF-β1 stimulation. MOX did, however, retard HCF-containing gel contractility and α-SMA filament formation following TGF-β1 stimulation in the pretreatment and co-treatment groups but not in the post-treatment group. MOX blocked the expression of Smad2, phospho-Smad2-Ser467 and TGFBR1 under TGF-β1 incubation. Additionally, MOX enhanced Smad7 expression in TGF-β1-incubated HCFs, but did not interfere with TGF-β-triggered Smad2 nuclear translocation or Smad4 expression.

CONCLUSIONS AND IMPLICATIONS

MOX inhibited TGF-β-induced fibroblast-to-myofibroblast differentiation via blocking TGFBR1 and enhancing Smad7 expression. MOX should be used before or during surgery to achieve these effects. These results suggest a de novo mechanism by which MOX participates in corneal wound healing.

Mitomycin C: biological effects and use in refractive surgery

PURPOSE

To provide an overview of the safety and efficacy of mitomycin C (MMC) as adjuvant therapy after refractive surgery procedures.

METHODS

Literature review.

RESULTS

Over the past 10 years, MMC has been used by refractive surgeons to prophylactically decrease haze after surface ablation procedures and therapeutically in the treatment of preexisting haze. Development of MMC treatments has had a significant role in the revival of surface ablation techniques. We reviewed the literature regarding mechanism of action of MMC, its role in modulating wound healing after refractive surgery, and its safety and efficacy as adjuvant therapy applied after primary photorefractive keratectomy surgery or after photorefractive keratectomy re-treatment after laser in situ keratomileusis and other corneal surgeries and disorders. The drug is a potent mitotic inhibitor that effectively blocks keratocyte activation, proliferation, and myofibroblast differentiation. Many studies have suggested that MMC is safe and effective in doses used by anterior surface surgeons, although there continue to be concerns regarding long-term safety. After initial depletion of anterior keratocytes, keratocyte density seems to return to normal 6 to 12 months after the use of MMC when corneas are examined with the confocal microscope. Most clinical studies found no difference between preoperative and postoperative corneal endothelial cell densities when MMC 0.02% was applied during refractive surgery, with exposure time of 2 minutes or less.

CONCLUSIONS

After more than 10 years of use, MMC has been found to be effective when used for prevention and treatment of corneal haze. Questions remain regarding optimal treatment parameters and long-term safety.

Keratocyte density 3 months, 15 months, and 3 years after corneal surface ablation with mitomycin C

PURPOSE

To study the effects of surface ablation with mitomycin C (MMC) on keratocyte population.

DESIGN

Prospective, nonrandomized, interventional, comparative case series.

METHODS

Thirty two eyes treated with surface ablation with 0.02% MMC were compared with nontreated eyes at Vissum Santa Hortensia, Madrid, Spain. Keratocyte density was measured with the Heidelberg Retina Tomograph II (Rostock Cornea Module) 3, 15, and 36 to 42 months after the surgery in the anterior, mid, and posterior stroma, and compared with control eyes.

RESULTS

Three months postoperatively, we found a lower stromal bed density compared to controls (16 993 ± 8001 vs 29 660 ± 5904 cells/mm(3), P = .0001), while there was a significantly higher cell density in the mid (30 783 ± 9300 vs 18 505 ± 1996 cells/mm(3), P = .0001) and deep stroma (30 268 ± 8321 vs 18 438 ± 2139 cells/mm(3), P = .0001). Three years after the surgery, the cellularity in the stromal bed had not significantly changed from the 3-month follow-up, but the density in the mid (18 889 ± 3474 cells/mm(3)) and posterior stroma (18 992 ± 3402 cells/mm(3)) had decreased to show no difference from controls. The mean cell density between the anterior, mid, and posterior stroma was not significantly different from controls 15 months and 3 years after the surgery.

CONCLUSION

Our study suggests that there is a reorganization of the stromal cell population soon after surface ablation with MMC, with a decrease in the stromal bed compensated initially with an increase in the mid and posterior stroma. Corneal cellularity tends to normalize over time, and 3 years postoperatively the mean cell density throughout the cornea seems to maintain normal values.

Mitomycin C: a promising agent for the treatment of canine corneal scarring

OBJECTIVE

To evaluate the safety and efficacy of mitomycin C (MMC) in prevention of canine corneal scarring.

METHODS

With an in vitro approach using healthy canine corneas, cultures of primary canine corneal fibroblasts or myofibroblasts were generated. Primary canine corneal fibroblasts were obtained by growing corneal buttons in minimal essential medium supplemented with 10% fetal bovine serum. Canine corneal myofibroblasts were produced by growing cultures in serum-free medium containing transforming growth factor β1 (1 ng/mL). Trypan blue assay and phase-contrast microscopy were used to evaluate the toxicity of three doses of MMC (0.002%, 0.02% and 0.04%). Real-time PCR, immunoblot, and immunocytochemistry techniques were used to determine MMC efficacy to inhibit markers of canine corneal scarring.

RESULTS

A single 2-min treatment of 0.02% or less MMC did not alter canine corneal fibroblast or keratocyte phenotype, viability, or growth. The 0.02% dose substantially reduced myofibroblast formation (up to 67%; P < 0.001), as measured by the change in RNA and protein expression of fibrosis biomarkers (α-smooth muscle actin and F-actin).

CONCLUSION

This in vitro study suggests that a single 2-min 0.02% MMC treatment to the canine corneal keratocytes is safe and may be useful in decreasing canine corneal fibrous metaplasia. In vivo studies are warranted.

Keratocyte density after laser-assisted subepithelial keratectomy with mitomycin C

PURPOSE

To study the effects of laser-assisted subepithelial keratectomy (LASEK) with mitomycin C (MMC) on the keratocyte population.

DESIGN

Prospective, nonrandomized, interventional, comparative case series.

METHODS

Fifty-six eyes treated at Vissum Santa Hortensia, Madrid, Spain, were included in the study. We compared 28 eyes treated with LASEK with intraoperative 0.02% MMC versus 28 non-treated eyes. Keratocyte density was measured 3 months after the surgery in the anterior, mid, and posterior stroma and was compared with the corresponding layers in the control eyes. The anterior layer in the LASEK group was compared with 2 layers in the control group: the most anterior stromal layer and the 80 μm-deep layer, because that was the mean ablation depth performed in eyes that underwent LASEK.

RESULTS

We found a statistically significantly lower keratocyte population in the most anterior stromal layer after LASEK with MMC compared with both the most anterior stromal layer and the 80 μm-deep layer in controls. On the contrary, the treated group showed a significantly higher keratocyte density in both the mid stroma and the deep stroma. The comparison between the average densities through the entire cornea showed a significantly higher keratocyte population in the LASEK with MMC group.

CONCLUSIONS

LASEK with MMC seems to cause a decrease in the anterior stromal cells 3 months after the surgery compared with nonoperated corneas. There seems to be a compensating proliferation of keratocytes in the deeper corneal layers, suggesting that the ability of keratocytes to repopulate the cornea is maintained after the surgical procedure.

The safety profile of alkylphosphocholines in the model of the isolated perfused vertebrate retina

BACKGROUND

Alkylphosphocholines (APCs) are synthetic phospholipid derivatives, and have been demonstrated to inhibit ocular cell proliferation in vitro and in vivo. Currently, they are applied clinically for their antitumoral and antiparasitic properties, but have not yet been implemented for clinical use in proliferative ophthalmic disorders. The purpose of this study was to assess the safety of APC in the ex vivo model of the isolated perfused vertebrate retina.

METHODS

Bovine retina preparations were perfused with an oxygen pre-equilibrated standard solution. The electroretinogram (ERG) was recorded using Ag/AgCl-electrodes. After recording stable b-wave amplitudes, an APC was applied at the following concentrations to the nutrient solution: 0.25 microM, 2.5 microM and 25 microM. To investigate the effects of APC on photoreceptor function, a test series at the same concentrations was performed to evaluate the effects of APC on the a-wave amplitude. Aspartate at a concentration of 1 mM was added to the nutrient solution to obtain stable a-wave amplitudes. Thereafter, APC was applied at the same concentrations to the nutrient solution. The recovery of the ERG amplitudes was followed up for 75 minutes.

RESULTS

No reduction of the a- and b-wave amplitude was found at the end of the exposure time with APC added in each test series. No differences were found between the ERG amplitudes before and after application of APC at the end of the washout.

CONCLUSIONS

In the ex vivo model of the isolated perfused vertebrate retina, APC has proved to be a safe compound in the concentrations applied. Thus, APCs should further be considered as promising candidates for future clinical applications in ophthalmology.

Dexamethasone reduces mitomycin C-related inflammatory cytokine expression without inducing further cell death in corneal fibroblasts

The purpose of this study was to investigate the effect of dexamethasone (DEX) on mitomycin C (MMC)-induced inflammatory cytokine expression in corneal fibroblasts. Primary human corneal fibroblasts were treated with MMC, dexamethasone, or in combination. Morphological changes and cell growth were documented using phase-contrast microscopy and PicoGreen assay, respectively. Cell apoptosis was evaluated by annexin V/propidium iodide staining, whereas viability was tested by the live/dead assay and analyzed by flow cytometry. The relative expression of interleukin-8 and monocyte chemoattractant protein-1 was investigated with quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay. Mitogen-activated protein kinase activation and mitogen-activated protein kinase phosphatase-1 expression were documented by Western blot analysis. We found that MMC induced corneal fibroblast elongation, apoptosis, and retarded cell growth, whereas DEX did not significantly alter cell morphology or viability. The combination of DEX and MMC did not induce additional apoptosis and cell death. DEX dose dependently down-regulated basal and MMC-induced interleukin-8 and monocyte chemoattractant protein-1 mRNA expression and protein secretion. DEX attenuated MMC-induced p38 and Jun N-terminal kinases activation and up-regulated expression. These suggested that DEX may inhibit MMC-induced interleukin-8 and monocyte chemoattractant protein-1 by up-regulating MKP-1 expression, which subsequently deactivated p38 and Jun N-terminal kinases activation. Combined MMC and DEX treatment may facilitate corneal wound healing.

Mitomycin C aqueous humor concentration after photorefractive keratectomy: an experimental study

PURPOSE

To evaluate mitomycin C (MMC) aqueous humor concentration after photorefractive keratectomy (PRK).

METHODS

In this experimental study, twenty-four eyes of 12 male pigmented rabbits were divided into 4 groups and studied at the Institute of Vision and Optics, Department of Medicine, University of Crete, Greece. Eyes in groups 1 and 2 underwent PRK to correct -5 diopters (D) in a 6-mm optical zone, while sponges soaked with 0.02% MMC were applied on the exposed corneal stroma for 60 and 120 seconds, respectively. Similarly, eyes in groups 3 and 4 underwent PRK to correct -10 D in a 6-mm optical zone, while sponges soaked with 0.02% MMC were applied on the exposed corneal stroma for 60 and 120 seconds, respectively. Aqueous humor was extracted from all rabbit eyes 10 minutes after MMC application and high-performance liquid chromatography was performed immediately to detect and quantify MMC levels.

RESULTS

The mean aqueous humor concentration of MMC was 0.23+/-0.03 microg/mL, 0.39+/-0.05 microg/mL, 0.28+/-0.04 microg/mL, and 0.52+/-0.16 microg/mL in groups 1, 2, 3, and 4, respectively. The effect of application time and correction on aqueous humor MMC concentration was significant (p<0.0001 and p=0.019), while the exposure time had a greater impact on aqueous humor MMC concentration when compared with the attempted correction.

CONCLUSIONS

Both exposure time of MMC on the corneal stroma and the attempted correction was correlated with MMC aqueous humor concentrations.

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.

Low-dose mitomycin C as a prophylaxis for corneal haze in myopic surface ablation

PURPOSE

To evaluate the efficacy of low-dose (0.002%) mitomycin C (MMC) vs no prophylactic MMC (control) in reducing corneal haze after surface laser ablation.

DESIGN

Two-year retrospective follow-up study performed in Jaipur, India.

METHODS

Ninety-two eyes with no MMC application and 83 eyes with 0.002% MMC application during laser epithelial keratomileusis (LASEK) were analyzed in a retrospective chart review with one month, two months, three months, six months, one year, and two years of postoperative follow-up. Postoperative haze, visual acuity, and efficacy ratio (EFFR) then were analyzed statistically.

RESULTS

The no-dose MMC and low-dose MMC groups were statistically similar except for a thinner corneal pachymetry (P < .001), higher spherical equivalent error (P = .006), and smaller ablation zone (P = .009) in eyes not treated with MMC when subjected to univariate analysis. Multivariate analysis was used to overcome the preoperative statistical differences among the two groups. Eyes treated with low-dose MMC (0.002%) demonstrated statistically less haze at all postoperative time points and in each myopic subgroup (P < .001). The postoperative uncorrected visual acuity (UCVA) and EFFR, however, showed no difference between the groups, except for better EFFR with MMC at one month (P < .001) and two months (P = .034).

CONCLUSIONS

Low-dose MMC (0.002%) in eyes after LASEK results in less corneal haze than in eyes not receiving this agent. Concerns regarding the potential toxicity of MMC make a 10-fold less concentration more desirable in refractive surgery. Further comparative study of low- vs higher-dose MMC is recommended to characterize its clinical benefit fully.

Alterations in endothelial cell density after photorefractive keratectomy with adjuvant mitomycin

PURPOSE

To elucidate the distinct role of the intraoperative use of mitomycin C (MMC) on endothelial cell density after photorefractive keratectomy (PRK) in human eyes.

DESIGN

Prospective, double-masked, randomized clinical trial.

METHODS

One eye of 15 patients was treated with PRK with intraoperative use of topical 0.02% MMC (15 seconds), whereas the fellow eye was treated with Epipolis laser in situ keratomileusis (Epi-LASIK) in random order. Corneal confocal microscopy was performed in all eyes preoperatively and at one, three, six, and 12 months after the surgery. Moreover, three endothelial images were acquired in each of 15 preoperative-normal eyes to evaluate the repeatability of measuring endothelial cell density. Repeated measures analysis of variance was used to compare the temporal variations of endothelial cell density between the two techniques and the changes of endothelial cell density over time.

RESULTS

The coefficient of repeatability of endothelial cell count was 148 cells/mm(2). Preoperative endothelial cell density was not significantly different between the two groups (P = .82). Moreover, the effect of the treatment on the temporal variation of endothelial cell density was insignificant (P = .83), whereas the differences between the preoperative and the postoperative endothelial cell densities reached statistical significance (P <or= .05). Nonetheless, inclusion of the repeatability of the instrument on the analysis diminished these significant differences (P > .05).

CONCLUSIONS

The prophylactic intraoperative application of MMC (up to 15 seconds) after PRK does not seem to affect the endothelial cell density.

Mitomycin-C Concentration in Cornea and Aqueous Humor and Apoptosis in the Stroma After Topical Mitomycin-C Application

PURPOSE

To evaluate the effects of the applied mitomycin-C (MMC) concentration and application time on the aqueous MMC concentration and apoptosis in the corneal stroma.

METHODS

New Zealand white rabbits underwent mechanical epithelium debridement of the central 7.5 mm of the cornea. A sponge soaked in MMC solution was placed on the denuded corneal stroma. The effect of the exposure times ranging from 15 to 120 seconds and the different MMC concentrations ranging from 0.005% to 0.04% on the aqueous MMC concentration and the apoptosis in the stromal cells were evaluated.

RESULTS

The aqueous concentration of MMC increased linearly with increasing exposure time and MMC concentration. The correlation between the aqueous MMC concentration and the applied concentration (r = 0.809, P < 0.001) was higher than the correlation between the aqueous MMC concentration and the application time (r = 0.693, P < 0.001). Terminal deoxyribonucleotidyltransferase-mediated dUTP-digoxigenin nick end labeling (TUNEL)-positive cells were detected in the superficial stroma of the central denuded cornea. The numbers of TUNEL-positive cells increased linearly with increasing concentrations, and the increase was statistically significant (P = 0.026). However, the numbers of TUNEL-positive cells increased only slightly with an increasing application time, and the increase was not statistically significant (P = 0.928).

CONCLUSIONS

Reducing the applied concentration or decreasing the exposure time might be a good modality for reducing the potential MMC toxicity. The applied MMC concentration had greater effects on the aqueous MMC concentration and apoptosis in the stromal cells than the exposure time.

Concentrations of Mitomycin C in Rabbit Corneal Tissue and Aqueous Humor After Topical Administration

PURPOSE

To study the aqueous and corneal pharmacokinetics of mitomycin C (MMC) after single topical administration to the central cornea and to evaluate the effects of different concentrations and different application times on the aqueous concentration of MMC.

METHODS

Mechanical epithelium debridement of the central 7.5 mm of the cornea was performed in New Zealand white rabbits, and a sponge soaked in 0.02% MMC solution was placed on the denuded corneal stroma for 2 minutes. Aqueous fluid and central corneal tissues samples were taken at 0.5, 1, 2, and 3 hours thereafter. MMC concentration of the samples was analyzed by high-performance liquid chromatography and evaluated at different exposure times (range: 15-120 seconds) and concentrations of applied MMC (range: 0.005%-0.04%).

RESULTS

Peak corneal concentration was 3.728 +/- 2.547 microg/g at 30 minutes after topical administration. Maximum aqueous concentration was 0.380 +/- 0.038 microg/mL at 1 hour after topical application. The aqueous concentration of MMC increased in a dose-dependent manner with increasing exposure time and application concentration. Aqueous MMC concentration increased at a higher rate with change of applied concentration than with exposure time.

CONCLUSION

Good penetration of MMC through central bare cornea may be noxious to endothelial cells. Reducing concentration or decreasing exposure time seems a good modality to reduce potential MMC toxicity.

Development of late-onset subepithelial corneal haze after laser-assisted subepithelial keratectomy with prophylactic intraoperative mitomycin-C

We present a case of dense, visually significant reticular haze that developed approximately 17 months after uneventful laser-assisted subepithelial keratectomy with mitomycin-C (MMC). The patient was successfully treated with manual debridement coupled with phototherapeutic keratectomy and intraoperative MMC.