Stromal haze, myofibroblasts, and surface irregularity after PRK

Topical delivery of aqueous micellar resolvin E1 analog (RX-10045)

PURPOSE

The primary objective of this study were to optimize aqueous micellar solution of isopropyl ester prodrug of resolvin (RX-10045), study in vivo ocular compatibility and tissue distribution following topical administration.

METHODS

An optimized ratio of hydrogenated castor-oil and octoxynol-40 (1.0:0.05 wt%) was prepared to entrap RX-10045 in the hydrophobic core of micelles. RX-10045 aqueous micelles were subjected to characterization. In vitro stability studies were performed at 4 °C, 25 °C and 40 °C. In vivo studies were conducted in New Zealand albino rabbits following topical drop administration.

RESULTS

Aqueous RX-10045 micellar solutions were successfully prepared. Micelles had a mean diameter of ∼12 nm with low negative surface charge. RX-10045 demonstrated high stability in citrate buffer (0.0 1M) at 40 °C. Hackett-McDonald ocular irritation scores were extremely low comparable to negative control. No significant difference in intraocular pressure was noted. Electroretinography studies did not reveal any retinal damage after multiple dosing of RX-10045 micellar solution. Ocular tissue distribution studies demonstrated appreciable drug concentrations in anterior ocular tissues. Moreover, RX-10008 (active metabolite of RX-10045) was detected in retina/choroid upon topical drop instillation.

CONCLUSIONS

A clear, stable, aqueous 0.1% RX-10045 micellar formulation was successfully prepared. Micellar solution was well-tolerated and did not have any measurable tissue damage in rabbit ocular tissues. Micelles appear to follow conjunctival/scleral pathway to reach back-of-the-eye tissue (retina). Topical aqueous formulations may be employed to treat posterior ocular diseases. Such micellar topical formulations may be more patient acceptable over invasive routes of administrations such as intravitreal injection/implants.

Corneal Complications During and After Vitrectomy for Retinal Detachment in Photorefractive Keratectomy Treated Eyes

To evaluate the occurrence of late-onset corneal haze (LOCH) after vitrectomy for rhegmatogenous retinal detachment (RRD) in photorefractive keratectomy (PRK)-treated eyes. This observational cohort study comprised 13 eyes of 13 patients who underwent vitrectomy for RRD and who had been subjected to PRK years earlier. The occurrence of LOCH was evaluated together with all the preoperative, intraoperative, and postoperative factors that could affect final corneal status. LOCH developed in 2 eyes. Both patients had undergone PRK for high myopia--one 3 years and the other 9 years prior to RRD. Both patients presented with RRD due to giant retinal tear and were subjected to scleral buckle, 20-gauge vitrectomy, and silicone oil tamponade. Three months after vitrectomy and 1 month after silicone oil removal they both developed LOCH. During vitreoretinal surgery neither of the 2 patients needed mechanical epithelial debridement. Intraoperative epithelial debridement was performed in 2 of the other patients of the series, who had undergone previous PRK for high myopia and had clear corneas at presentation; in 1 of them this manoeuvre hampered intraoperative visualization. Follow-up after retinal detachment surgery ranged from 6 to 156 months (mean, 37.5 months). Subepithelial corneal scarring may be reactivated many years after PRK. In our series this happened after vitrectomy.

Corneal wound healing after laser vision correction

Any trauma can trigger a cascade of responses in tissues, with the purpose of safeguarding the integrity of the organ affected by the trauma and of preventing possible damage to nearby organs. Subsequently, the body tries to restore the function of the organ affected. The introduction of the excimer laser for keratorefractive surgery has changed the treatment landscape for correcting refractive errors, such as myopia, hyperopia, and astigmatism. In recent years, with the increased understanding of the basic science of refractive errors, higher-order aberrations, biomechanics, and the biology of corneal wound healing, a reduction in the surgical complications of keratorefractive surgery has been achieved. The understanding of the cascade of events involved in the corneal wound healing process and the examination of how corneal wound healing influences corneal biomechanics and optics are crucial to improving the efficacy and safety of laser vision correction.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Anti-Apoptotic Gene Delivery with cyclo-(d-Trp-Tyr) Peptide Nanotube via Eye Drop Following Corneal Epithelial Debridement

Corneal keratocyte apoptosis triggered by cornel debridement is one mechanism of corneal disorders. In this study, the feasibility of cyclo-(d-Trp-Tyr) peptide nanotubes (PNTs) as carriers of caspase 3 silence shRNA delivery was assessed. A model of epithelial injury by epithelial debridement was applied to investigate the feasibility of PNTs as gene delivery carriers on corneal injury. First, the PNTs were found within 2 μm in length and 300 nm in width by an atomic force microscope and confocal laser microscope system. Plasmid DNAs were observed to be associated with PNTs by atomic force microscope and confocal laser scanning microscope. The plasmids were associated with tyrosine of PNTs with a binding constant of 2.7 × 108 M-1. The stability of plasmid DNA with PNTs against the DNase was found at 60 min. Using thioflavin T pre-stained PNTs on the corneal eye drop delivery, the distribution of PNTs was in the epithelial and stroma regions. After corneal debridement, the rhodamine-labeled plasmid DNA and thioflavin T pre-stained PNTs were also delivered and could be observed in the stroma of cornea. PNTs complexed with anti-apoptotic plasmid caspase 3 silencing shRNA eye drop delivery decreased 41% of caspase 3 activity after the first dose by caspase 3 activity and Western blot analysis.

Corneal Regeneration After Photorefractive Keratectomy: A Review

Photorefractive keratectomy (PRK) remodels corneal stroma to compensate refractive errors. The removal of epithelium and the ablation of stroma provoke the disruption of corneal nerves and a release of several peptides from tears, epithelium, stroma and nerves. A myriad of cytokines, growth factors, and matrix metalloproteases participate in the process of corneal wound healing. Their balance will determine if reepithelization and stromal remodeling are appropriate. The final aim is to achieve corneal transparency for restoring corneal function, and a proper visual quality. Therefore, wound-healing response is critical for a successful refractive surgery. Our goal is to provide an overview into how corneal wounding develops following PRK. We will also review the influence of intraoperative application of mitomycin C, bandage contact lenses, anti-inflammatory and other drugs in preventing corneal haze and post-PRK pain.

Effects of new biomimetic regenerating agents on corneal wound healing in an experimental model of post-surgical corneal ulcers

OBJECTIVE

The purpose of this study is to assess the effectiveness of the topical application of cacicol regenerating agent (RGTA) in an experimental model of corneal ulcer after photorefractive keratectomy (PRK) in mice.

METHODS

Mice were subjected to PRK surgery with a 2.0mm ablation zone on the central cornea and 45mm of depth on a VISX Star S2 excimer laser. Corneas were treated topically with cacicol drops 1hour and 48hours after injury. Control groups received balanced salt solution (BSS) in the same dosage. Clinical and histopathological events were evaluated at 1, 2, 3 and 7 days after surgery. Sections obtained through the central region of the corneas were used to analyze the histopathological events of injured and healed corneas. αSMA (myofibroblast transformation), E cadherin (assembly of epithelial cells) and neuronal class III β-tubulin (innervation) were performed.

RESULTS

Corneas treated topically with cacicol for 7 days showed a greater degree of transparency compared to controls. cacicol treated corneas showed improved epithelial cytoarchitecture. Analysis of αSMA profiles in the stroma showed that cacicol reduced or delayed the presence of myofibroblasts in the stroma compared to BSS (P<0.001). Finally, a putative neuroregenerative effect of cacicol was found in corneas subjected to an experimental PRK lesion. In some cases some interindividual variability could be observed due to the design of the experimental model. This is a limitation to consider, despite the statistical significance of the data.

CONCLUSIONS

In a model of laser induced surgical lesions in the cornea, topical application of an RGTA (i.e. cacicol) could be involved in avoiding myofibroblast scarring formation and promoting nerve regeneration.

One-year outcomes of small-incision lenticule extraction (SMILE): mild to moderate myopia vs. high myopia

Background

The purpose of this study was to compare the refractive outcomes of small incision lenticule extraction (SMILE) in high-myopic patients with those of mild- to moderate-myopic patients.

Methods

This study included 183 eyes of 92 myopic patients treated with SMILE using a VisuMax 500-kHz femtosecond laser. Treated eyes were divided into two groups, according to the preoperative spherical equivalent (SE): mild to moderate myopia (A group, <−6.0 D) and high myopia (B group, ≥ − 6.0 D). Follow-up visits were at 1 day, 1 week, and 1, 3, 6, and 12 months. The outcome measures included uncorrected distance visual acuity (UDVA), best-corrected distance visual acuity (BDVA), postoperative SE, efficacy index, safety index, and predictability.

Results

Preoperative SE was −5.05 ± 0.71 D in the A group and −7.67 ± 1.01 D in the B group. No differences were observed between −0.13 ± 0.38 D in the A group and −0.24 ± 0.35 D in the B group 12 months postoperatively (p = 0.18). At 12 months postoperatively, 93.1 % and 76.8 % had an UDVA of 20/20 or better in the A and B groups, respectively. In the A group, 87.9 % and 96.6 % were within ±0.5 D and ±1.0 D, respectively, of the intended correction; in the B group, 88.0 % and 97.6 % were within ±0.5 D and ±1.0 D, respectively. The efficacy index was 1.04 ± 0.19 in the A group and 0.99 ± 0.19 in the B group. The safety index was 1.27 ± 0.17 for the A group and 1.24 ± 0.17 for the B group. The efficacy and safety index were not significantly different between the two groups 12 months postoperatively (p = 0.141 and p = 0.307, respectively).

Conclusions

This study showed that SMILE is effective and safe for correcting high myopia, as well as mild to moderate myopia.

Epithelial basement membrane proteins perlecan and nidogen-2 are up-regulated in stromal cells after epithelial injury in human corneas

The epithelial basement membrane (BM) is a specialized extracellular matrix that has been shown to have a critical role in corneal development, wound healing, and disease. Although the epithelial BM contributes to corneal homeostasis, relatively little is know about non-epithelial production of its components that may be important in defective regeneration of the epithelial basement membrane associated with opacity after photorefractive keratectomy. The purpose of the current study was to investigate stromal production of corneal epithelial BM proteins in wounded human corneas using immunohistochemistry. A total of five unwounded control eyes and five 30-min epithelial-wounded corneas were obtained from fresh corneoscleral buttons removed from human eyes enucleated due to choroidal melanoma with normal anterior segments. In the wounded corneas, an eight mm patch of central corneal epithelium and epithelial BM was removed with a Beaver blade when the patient was under general anesthesia. Immunohistochemical analyses were performed to detect perlecan and nidogen-2 proteins-important components of the epithelial BM lamina lucida and lamina densa zones. Perlecan and nidogen-2 proteins were detected in the BM itself and at low levels in keratocytes in all unwounded corneas. After epithelial injury, both perlecan and nidogen-2 were expressed at high levels in stromal keratocytes, including superficial keratocytes in the early phases of apoptosis. Thus, after epithelial and epithelial BM injury, stromal keratocytes contribute important perlecan and nidogen-2 components to the regenerating epithelial BM.

Tissue reaction after intrastromal corneal ring implantation in an experimental animal model

PURPOSE

To evaluate corneal wound healing in the hen animal model after additive surgery with an intracorneal ring segment (ICRS).

METHODS

We implanted one ICRS in each eye of 76 hens. In control group 1 (n = 22 hens), the stromal channel was prepared but no ICRS was inserted. In control group 2 (n = 2 hens), no surgery was performed. Animals were randomly separated into groups and euthanized after clinical follow-up of 4 and 12 hours, 1, 2, 3, and 7 days, and 1, 2, 3, 4, and 6 months. Corneas were stained with hematoxylin-eosin. Apoptosis was measured by terminal uridine nick end-labeling assays. Cell proliferation and myofibroblast-like differentiation were assayed by BrdU and α-smooth muscle actin immunofluorescence microscopy. Stromal matrix changes were documented by electron microscopy.

RESULTS

Epithelial and stromal cell apoptosis around the ICRS-implanted and control group 1 eyes peaked at 12 hours, but continued for 72 hours. In ICRS-implanted eyes, epithelial and stromal proliferation was present at 12 and 24 hours, respectively, and peaked at 7 days and 72 hours, respectively. Some proliferation in the ICRS-implanted group continued through the 6-month follow-up, and myofibroblast-like cells differentiated one to three months after ICRS implantation. The segments rotated within the stroma as the limbal inferior angle approached the epithelium.

CONCLUSIONS

Wound healing after ICRS implantation in hen corneas was similar to that of other corneal surgical wounds in stages. However, there were some specific features related to the small size of the epithelial wound and the device permanently implanted inside the cornea.

Resolvin E1 analog RX-10045 0.1% reduces corneal stromal haze in rabbits when applied topically after PRK

PURPOSE

To perform a masked study to determine whether resolvin E1 (RvE1), a lipid-derived immunomodulator, could regulate the development of corneal haze and opacity-related myofibroblasts after opacity-generating high correction photorefractive keratectomy (PRK) in rabbits.

METHODS

Three groups of eight rabbits each were included in the study. Nine diopter (D) PRK for myopia was performed in each test cornea, and the eyes were treated with 30 µl of topical solution every 4 h (six times a day) for 5 days starting immediately after PRK. Group 1 was treated with 0.1% RX-10045, a prodrug of an RvE1 analog; group 2 was treated with 0.01% RX-10045; and group 3 was treated with vehicle control solution. At 1 month after PRK, haze was graded at the slit-lamp by a masked observer. Immunohistochemistry for α-smooth muscle actin (SMA) was performed on the central cornea of each test eye to determine the anterior stromal myofibroblast density.

RESULTS

Corneal opacity was significantly lower in the 0.1% RX-10045 group, but not the 0.01% RX-10045 group, compared to the vehicle control group (p=0.029), at 1 month after -9.0D PRK. At 1 month after -9.0D PRK, SMA+ myofibroblast densities in the anterior stroma were not statistically significantly different among the three groups, although a trend toward lower myofibroblast generation was noted in the 0.1% RX-10045 group.

CONCLUSIONS

Topical 0.1% RX-10045, a prodrug of an RvE1 analog, reduces corneal opacity after haze-generating PRK in rabbits. Further studies are needed to determine the precise points at which RvE1 decreases corneal opacity after injury.

Cellular and extracellular matrix modulation of corneal stromal opacity

Stromal transparency is a critical factor contributing to normal function of the visual system. Corneal injury, surgery, disease and infection elicit complex wound healing responses that serve to protect against insults and maintain the integrity of the cornea, and subsequently to restore corneal structure and transparency. However, in some cases these processes result in prolonged loss of corneal transparency and resulting diminished vision. Corneal opacity is mediated by the complex actions of many cytokines, growth factors, and chemokines produced by the epithelial cells, stromal cells, bone marrow-derived cells, lacrimal tissues, and nerves. Myofibroblasts, and the disorganized extracellular matrix produced by these cells, are critical determinants of the level and persistence of stromal opacity after corneal injury. Decreases in corneal crystallins in myofibroblasts and corneal fibroblasts contribute to cellular opacity in the stroma. Regeneration of a fully functional epithelial basement membrane (BM) appears to have a critical role in the maintenance of corneal stromal transparency after mild injuries and recovery of transparency when opacity is generated after severe injuries. The epithelial BM likely has a regulatory function whereby it modulates epithelium-derived growth factors such as transforming growth factor (TGF) β and platelet-derived growth factor (PDGF) that drive the development and persistence of myofibroblasts from precursor cells. The purpose of this article is to review the factors involved in the maintenance of corneal transparency and to highlight the mechanisms involved in the appearance, persistency and regression of corneal opacity after stromal injury.

Assessment of anti-scarring therapies in ex vivo organ cultured rabbit corneas

The effects of a triple combination of siRNAs targeting key scarring genes were assessed using an ex vivo organ culture model of excimer ablated rabbit corneas. The central 6 mm diameter region of fresh rabbit globes was ablated to a depth of 155 microns with an excimer laser. Corneas were excised, cultured at the air-liquid interface in defined culture medium supplemented with transforming growth factor beta 1 (TGFB1), and treated with either 1% prednisolone acetate or with 22.5 μM cationic nanoparticles complexed with a triple combination of siRNAs (NP-siRNA) targeting TGFB1, TGFB Receptor (TGFBR2) and connective tissue growth factor (CTGF). Scar formation was measured using image analysis of digital images and levels of smooth muscle actin (SMA) were assessed in ablated region of corneas using qRT-PCR and immunostaining. Ex vivo cultured corneas developed intense haze-like scar in the wounded areas and levels of mRNAs for pro-fibrotic genes were significantly elevated 3-8 fold in wounded tissue compared to unablated corneas. Treatment with NP-siRNA or steroid significantly reduced quantitative haze levels by 55% and 68%, respectively, and reduced SMA mRNA and immunohistostaining. This ex vivo corneal culture system reproduced key molecular patterns of corneal scarring and haze formation generated in rabbits. Treatment with NP-siRNAs targeting key scarring genes or an anti-inflammatory steroid reduced corneal haze and SMA mRNA and protein.

Genomics of corneal wound healing: a review of the literature

Corneal wound healing is a complex process: its mechanisms and the underlying genetic control are not fully understood. It involves the integrated actions of multiple growth factors, cytokines and proteases produced by epithelial cells, stromal keratocytes, inflammatory cells and lacrimal gland cells. Following an epithelial insult, multiple cytokines are released triggering a cascade of events that leads to repair the epithelial defect and remodelling of the stroma to minimize the loss of transparency and function. In this review, we examine the literature surrounding the genomics of corneal wound healing with respect to the following topics: epithelial and stromal wound healing (including inhibition); corneal neovascularisation; the role of corneal nerves in wound healing; the endothelium; the role of aquaporins and aptamers. We also examine the effect of ectasia on corneal wound healing with regard to keratoconus and following corneal surgery. A better understanding of the cellular and molecular changes that occur during repair of corneal wounds will provide the opportunity to design treatments that selectively modulate key phases of the healing process resulting in scars that more closely resemble normal corneal architecture.

Long term followup of photorefractive keratectomy with adjuvant use of mitomycin C

Purpose. To study the long term refractive and visual outcomes of photorefractive keratectomy (PRK) with intraoperative application of mitomycin C (MMC). Methods. This study included 37 eyes who received myopic PRK; after photoablation, a sponge soaked in 0.02% MMC solution was applied in all corneas for 2 minutes. Efficacy, safety, predictability, and stability of PRK MMC were evaluated. Endothelial cell density was evaluated at the last postoperative interval. Results. Mean preoperative spherical equivalent (SEQ) was −6.03 ± 1.87 D (diopters) and reduced to −0.09 ± 0.53 D at the last postoperative examination. Mean followup was 44.73 ± 18.24 months. All the eyes were in the ±1.00 D of attempted versus achieved SEQ at the one-year follow-up interval. Furthermore, 95% of the eyes did not lose lines or gained 1 to 2 lines of CDVA, while 5% lost 1 line. At the third postoperative month, 89% of the eyes either were clear or had trace haze, while 4 eyes had mild haze; by the 12-month postoperative interval, none of the eyes demonstrated haze. Mean endothelial cell density (ECD) at the last postoperative interval was 2658 ± 153 cells/mm². Conclusions. PRK, with intraoperative use of MMC, demonstrates stable refractive and visual outcomes up to 44 months after surgery.

Wounding the cornea to learn how it heals

Corneal wound healing studies have a long history and rich literature that describes the data obtained over the past 70 years using many different species of animals and methods of injury. These studies have lead to reduced suffering and provided clues to treatments that are now helping patients live more productive lives. In spite of the progress made, further research is required since blindness and reduced quality of life due to corneal scarring still happens. The purpose of this review is to summarize what is known about different types of wound and animal models used to study corneal wound healing. The subject of corneal wound healing is broad and includes chemical and mechanical wound models. This review focuses on mechanical injury models involving debridement and keratectomy wounds to reflect the authors' expertise.

Refractive change in the adult rabbit eye after corneal relaxation with the femtosecond laser

BACKGROUND

A new procedure to correct myopia that does not disturb the cornea in the optical zone and avoids injuring the corneal epithelium could be a key advance in corneal refractive surgery. The aim of this study is to observe the refractive change in the adult rabbits undergoing femtosecond laser-assisted multilayer intrastromal ablation in the mid-periphery of the cornea without injury of epithelium.

METHOD

The right eyes of 8 New Zealand White adult rabbits were used for the experiments. A 60-kHz femtosecond laser delivery system was used, and three lamellar layers of laser pulses were focused starting at a corneal depth of 180 μm and ending at 90 μm from the surface, with each successive layer placed 45 μm anterior to the previous layer. In the interface of the applanation contact lens cone, a 6-mm diameter aluminum circle was placed at the center to block the laser, limiting ablation to the mid-periphery of the cornea. The laser settings were as follows: spot/line separation, 10 μm; diameter, 8.0 mm; energy for ablating the stroma, 1.3 μJ. An authorefractor was used to assess the manifest refraction.

RESULTS

Mean spherical equivalent (SE) (mean ± SD, SD: standard deviation) was significantly increased at postoperative week 1 (1.67 ± 0.26 D, p < 0.0001), month 1 (1.65 ± 0.23 D, p < 0.0001), and month 3 (1.60 ± 0.22 D, p < 0.0001) compared to baseline (0.68 ± 0.27 D). Mean spherical equivalent showed no significant change between postoperative week 1 and month 3 (p = 0.1168).

CONCLUSION

Femtosecond laser-assisted multilayer corneal intrastromal ablation in the mid-periphery may cause a consequent hyperopic shift with no refractive regression.

The corneal epithelial basement membrane: structure, function, and disease

The corneal epithelial basement membrane (BM) is positioned between basal epithelial cells and the stroma. This highly specialized extracellular matrix functions not only to anchor epithelial cells to the stroma and provide scaffolding during embryonic development but also during migration, differentiation, and maintenance of the differentiated epithelial phenotype. Basement membranes are composed of a diverse assemblage of extracellular molecules, some of which are likely specific to the tissue where they function; but in general they are composed of four primary components--collagens, laminins, heparan sulfate proteoglycans, and nidogens--in addition to other components such as thrombospondin-1, matrilin-2, and matrilin-4 and even fibronectin in some BM. Many studies have focused on characterizing BM due to their potential roles in normal tissue function and disease, and these structures have been well characterized in many tissues. Comparatively few studies, however, have focused on the function of the epithelial BM in corneal physiology. Since the normal corneal stroma is avascular and has relatively low keratocyte density, it is expected that the corneal BM would be different from the BM in other tissues. One function that appears critical in homeostasis and wound healing is the barrier function to penetration of cytokines from the epithelium to stroma (such as transforming growth factor β-1), and possibly from stroma to epithelium (such as keratinocyte growth factor). The corneal epithelial BM is also involved in many inherited and acquired corneal diseases. This review examines this structure in detail and discusses the importance of corneal epithelial BM in homeostasis, wound healing, and disease.

Topical rosiglitazone is an effective anti-scarring agent in the cornea

Corneal scarring remains a major cause of blindness world-wide, with limited treatment options, all of which have side-effects. Here, we tested the hypothesis that topical application of Rosiglitazone, a Thiazolidinedione and ligand of peroxisome proliferator activated receptor gamma (PPARγ), can effectively block scar formation in a cat model of corneal damage. Adult cats underwent bilateral epithelial debridement followed by excimer laser ablation of the central corneal stroma to a depth of ~160 µm as a means of experimentally inducing a reproducible wound. Eyes were then left untreated, or received 50 µl of either 10 µM Rosiglitazone in DMSO/Celluvisc, DMSO/Celluvisc vehicle or Celluvisc vehicle twice daily for 2 weeks. Cellular aspects of corneal wound healing were evaluated with in vivo confocal imaging and post-mortem immunohistochemistry for alpha smooth muscle actin (αSMA). Impacts of the wound and treatments on optical quality were assessed using wavefront sensing and optical coherence tomography at 2, 4, 8 and 12 weeks post-operatively. In parallel, cat corneal fibroblasts were cultured to assess the effects of Rosiglitazone on TGFβ-induced αSMA expression. Topical application of Rosiglitazone to cat eyes after injury decreased αSMA expression and haze, as well as the induction of lower-order and residual, higher-order wavefront aberrations compared to vehicle-treated eyes. Rosiglitazone also inhibited TGFβ-induced αSMA expression in cultured corneal fibroblasts. In conclusion, Rosiglitazone effectively controlled corneal fibrosis in vivo and in vitro, while restoring corneal thickness and optics. Its topical application may represent an effective, new avenue for the prevention of corneal scarring with distinct advantages for pathologically thin corneas.

Biological and biomechanical responses to traditional epithelium-off and transepithelial riboflavin-UVA CXL techniques in rabbits

PURPOSE

To compare the biological effects of riboflavin-ultraviolet A (UVA) corneal cross-linking (CXL) performed with a traditional epithelium-off method to several transepithelial methods in a rabbit model. Preliminary experiments on biomechanical rigidity were also performed.

METHODS

Four treatment groups were included: (1) standard epithelium-off, (2) tetracaine transepithelial, (3) benzal-konium chloride-ethylenediaminetetraacetic acid (BKC-EDTA) transepithelial, and (4) femtosecond laser-assisted transepithelial riboflavin-UVA CXL. Six eyes from each treatment group and the untreated control group were analyzed at 24 hours and 2 months after treatment in wound healing studies. The TUNEL assay was performed to detect the extent of stromal cell death. Optical density was measured with a Scheimpflug analyzer. The corneal stiffening effect was quantitated in three eyes from each group using optical coherence elastography performed 2 months after treatments.

RESULTS

Twenty-four hours after CXL, stromal cell death extended full corneal thickness with both standard epithelium-off CXL and femtosecond laser-assisted CXL, but only approximately one-third stromal depth after BKC-EDTA transepithelial CXL. Negligible stromal cell death was detected with tetracaine transepithelial CXL. Cell death results were statistically different between the BKC-EDTA transepithelial CXL and standard epithelium-off CXL groups (P < .0001). Significant corneal opacity differences were noted. Standard epithelium-off CXL had the greatest density and tetracaine transepithelial CXL had the least density compared to the control group after treatment. As measured with optical coherence elastography, a trend toward greater mean stiffening was observed with BKC-EDTA transepithelial CXL than with epithelium-off CXL, femtosecond laser-assisted CXL, or tetracaine transepithelial CXL, but the result did not reach statistical significance. All of the CXL treatment groups exhibited significantly smaller variance of stiffness compared to the control group.

CONCLUSION

In the rabbit model, BKC-EDTA transepithelial CXL produced less stromal cell death and less risk of endothelial cell damage than standard epithelium-off CXL or femtosecond laser-assisted CXL. Additional study is needed to determine whether biomechanical stiffness is significantly different between the epithelium-off CXL and transepithelial CXL groups.

Transmission electron microscopy analysis of epithelial basement membrane repair in rabbit corneas with haze

PURPOSE

To assess the ultrastructure of the epithelial basement membrane using transmission electron microscopy (TEM) in rabbit corneas with and without subepithelial stroma opacity (haze).

METHODS

Two groups of eight rabbits each were included in this study. Photorefractive keratectomy (PRK) was performed using an excimer laser. The first group had -4.5-diopter (-4.5D) PRK and the second group had -9.0D PRK. Contralateral eyes were unwounded controls. Rabbits were sacrificed at 4 weeks after surgery. Immunohistochemical analysis was performed to detect the myofibroblast marker α-smooth muscle actin (SMA). TEM was performed to analyze the ultrastructure of the epithelial basement membrane and stroma.

RESULTS

At 4 weeks after PRK, α-SMA+ myofibroblasts were present at high density in the subepithelial stroma of rabbit eyes that had -9.0D PRK, along with prominent disorganized extracellular matrix, whereas few myofibroblasts and little disorganized extracellular matrix were noted in eyes that had -4.5D PRK. The epithelial basement membrane was irregular and discontinuous and lacking typical morphology in all corneas at 1 month after -9D PRK compared to corneas at 1 month in the -4.5D PRK group.

CONCLUSIONS

The epithelial basement membrane acts as a critical modulator of corneal wound healing. Structural and functional defects in the epithelial basement membrane correlate to both stromal myofibroblast development from precursor cells and continued myofibroblast viability, likely through the modulation of epithelial-stromal interactions mediated by cytokines. Prolonged stromal haze in the cornea is associated with abnormal regeneration of the epithelial basement membrane.

New method of microwave thermokeratoplasty to correct myopia in 33 eyes: one-year results

PURPOSE

To assess the safety, predictability, and stability of a new microwave thermokeratoplasty procedure to correct myopia.

SETTING

Cornea and refractive surgery subspecialty.

DESIGN

Prospective clinical trial.

METHOD

Thermokeratoplasty was performed in myopic eyes at a single center in Turkey from June 2009 to June 2010. The attempted corrections ranged from -1.25 to -5.75 diopters (D). The main outcome measures were changes in logMAR uncorrected distance visual acuity (UDVA) and in keratometry (K) values.

RESULTS

The procedure was performed in 33 eyes (patients aged 20 to 45 years). The mean preoperative logMAR UDVA (0.76 ± 0.24 [SD]) significantly improved to 0.19 ± 0.20 at 1 month, postoperatively. By 3 months, the mean UDVA had markedly regressed to 0.59 ± 0.29; however, the residual improvement remained statistically significant. At 12 months, the mean logMAR UDVA was 0.72 ± 0.26. The mean K values were 43.9 ± 1.36 D preoperatively, 41.25 ± 2.63 D at 1 month, 43.4 ± 1.69 D at 3 months, and 44.1 ± 1.09 D at 12 months. The mean endothelial cell density was 2836 ± 342 cells/mm(2) preoperatively and were statistically unchanged 12 months postoperatively (2732 ± 353 cell/mm(2)). No patient lost lines of corrected distance visual acuity by 12 months postoperatively.

CONCLUSIONS

The new thermokeratoplasty procedure produced the desired reduction in myopia and improvement in postoperative UDVA 1 month postoperatively without significant side effects. However, early and complete regression shows the need for further development of this technique.

FINANCIAL DISCLOSURE

Drs. Yilmaz and Marshall are paid consultants to Avedro, Inc., and Dr. Muller is president and CEO of Avedro, Inc. No other author has a financial or proprietary interest in any material or method mentioned.

Ectopic epithelial implants following surface ablation of the cornea

PURPOSE

To determine the direct contribution of the epithelium to the generation of complications using a phototherapeutic keratectomy model.

METHODS

A mouse model with a genetically labeled epithelium was used to determine whether any epithelium-derived cells persist in the stroma up to 1 month after surgery. Also, gross histology and macrophotography of excimer-ablated rabbit corneas were analyzed for evidence epithelial ingrowths into the stroma.

RESULTS

Epithelium-derived cells were present in the wounded stroma 1 month after surgery. Micrographs taken during the first 4 days during healing evidenced epithelial invasion of the stroma in one and sometimes more locations in the same cornea. Gross histology also revealed that the epithelial invasions can result in complete delamination of stromal tissue and subsequent inclusion of the stromal material in the epithelium. The epithelial inclusions ultimately created a highly irregular corneal surface.

CONCLUSIONS

Ectopic epithelia are a known complication of LASIK and LASIK-like procedures. The data presented here indicate that ectopic epithelia are also a complication of surface ablation techniques. The knowledge that these complications are present following surface ablations provides a new understanding of the biological response to surface ablation techniques and suggests new avenues of study to improve clinical outcomes of those for whom LASIK-based techniques are not an option.

Very late-onset corneal scar triggered by trauma after photorefractive keratectomy

A 54-year-old woman who had photorefractive keratectomy (PRK) more than 10 years earlier presented with a history of being hit in the eye by a tree branch and developing blurred vision a short time later. The corrected visual acuity was 20/100 with localized grade 3 stromal haze. The haze intensified despite initial response to corticosteroids and cyclosporine, and treatment with phototherapeutic keratectomy and 0.02% mitomycin-C (MMC) was effective in restoring corneal clarity and normal vision. Late-onset stromal scar can be triggered by trauma years after PRK. Phototherapeutic keratectomy with MMC can be an effective treatment for late-onset scar. Persistent haze or scar after trauma if PRK had not been performed previously is exceedingly rare.

Control of scar tissue formation in the cornea: strategies in clinical and corneal tissue engineering

Corneal structure is highly organized and unified in architecture with structural and functional integration which mediates transparency and vision. Disease and injury are the second most common cause of blindness affecting over 10 million people worldwide. Ninety percent of blindness is permanent due to scarring and vascularization. Scarring caused via fibrotic cellular responses, heals the tissue, but fails to restore transparency. Controlling keratocyte activation and differentiation are key for the inhibition and prevention of fibrosis. Ophthalmic surgery techniques are continually developing to preserve and restore vision but corneal regression and scarring are often detrimental side effects and long term continuous follow up studies are lacking or discouraging. Appropriate corneal models may lead to a reduced need for corneal transplantation as presently there are insufficient numbers or suitable tissue to meet demand. Synthetic optical materials are under development for keratoprothesis although clinical use is limited due to implantation complications and high rejection rates. Tissue engineered corneas offer an alternative which more closely mimic the morphological, physiological and biomechanical properties of native corneas. However, replication of the native collagen fiber organization and retaining the phenotype of stromal cells which prevent scar-like tissue formation remains a challenge. Careful manipulation of culture environments are under investigation to determine a suitable environment that simulates native ECM organization and stimulates keratocyte migration and generation.

Establishment of an untransfected human corneal stromal cell line and its biocompatibility to acellular porcine corneal stroma

AIM

To establish an untransfected human corneal stromal (HCS) cell line and characterize its biocompatibility to acellular porcine corneal stroma (aPCS).

METHODS

Primary culture was initiated with a pure population of HCS cells in DMEM/F12 media (pH 7.2) containing 20% fetal bovine serum and various necessary growth factors. The established cell line was characterized by growth property, chromosome analysis, tumorigenicity assay, expression of marker proteins and functional proteins. Furthermore, the biocompatibility of HCS cells with aPCS was examined through histological and immunocytochemistry analyses and with light, electron microscopies.

RESULTS

HCS cells proliferated to confluence 2 weeks later in primary culture and have been subcultured to passage 140 so far. A continuous untransfected HCS cell line with a population doubling time of 41.44 hours at passage 80 has been determined. Results of chromosome analysis, morphology, combined with the results of expression of marker protein and functional proteins suggested that the cells retained HCS cell properties. Furthermore, HCS cells have no tumorigenicity, and with excellent biocompatibility to aPCS.

CONCLUSION

An untransfected and non-tumorigenic HCS cell line has been established, and the cells maintained positive expression of marker proteins and functional proteins. The cell line, with excellent biocompatibility to aPCS, might be used for in vitro reconstruction of tissue-engineered HCS.

Corneal myofibroblast biology and pathobiology: generation, persistence, and transparency

Important advances have led to a better understanding of the biology and pathobiology of corneal myofibroblasts and their generation after surgery, injury, infection and disease. Transforming growth factor (TGF) beta, along with platelet-derived growth factor (PDGF) and interleukin (IL)-1, has been shown to regulate myofibroblast development and death in in-vitro and in-situ animal models. The myofibroblast precursor cells regulated by these cytokines include both keratocyte-derived and bone marrow-derived cells. Cytokines that promote and maintain myofibroblasts associated with late haze after photorefractive keratectomy are modulated in part by the epithelial basement membrane functioning as barrier between the epithelium and stroma. Structural and functional defects in the basement membrane likely lead to prolonged elevation of TGFβ, and perhaps other cytokine, levels in the stroma necessary to promote differentiation of myofibroblasts. Conversely, repair of the epithelial basement membrane likely leads to a decrease in stromal TGFβ levels and apoptosis of myofibroblasts. Repopulating keratocytes subsequently reorganize the associated fibrotic extracellular matrix deposited in the anterior stroma by the myofibroblasts. Investigations of myofibroblast biology are likely to lead to safer pharmacological modulators of corneal wound healing and transparency.

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.

Stromal fibroblast-bone marrow-derived cell interactions: implications for myofibroblast development in the cornea

The purpose of this study was to test the hypothesis that mouse corneal stromal fibroblast and bone marrow-derived cell interactions augment corneal myofibroblast generation and, if so, to study whether such interactions are mediated by paracrine or juxtacrine mechanisms. Mouse bone marrow-derived cells and mouse corneal stromal fibroblasts were obtained from both mice with green fluorescent protein (GFP) expressed in all cells and normal GFP- BL6 control mice. To study the interactions of the different cell types, GFP+ cells of one type were co-cultured with GFP- cells of the other type in Primaria plates (to monitor juxtacrine signaling) or Transwell System plates (to monitor paracrine effects mediated by soluble mediators). Both cell types were cultured at a cell density of 1 × 10(5) cells per ml. The percentage of alpha smooth muscle actin+ myofibroblasts was significantly higher (ANOVA, p<0.001) when bone marrow-derived cells and mouse corneal stromal fibroblasts were co-cultured compared to when bone marrow-derived cells and mouse corneal stromal fibroblasts were cultured alone (control). The in vitro studies using GFP+ corneal fibroblasts or GFP+ bone marrow-derived cells demonstrated conclusively that both cells types could transform into myofibroblasts. However, the percentage of alpha smooth muscle actinassds+ myofibroblasts generated from either cell type precursor was higher when both cells were co-cultured together (juxtacrine) as compared to when bone marrow-derived cells and mouse corneal stromal fibroblasts were co-culture in different compartments of Transwell System (paracrine). Thus, more alpha smooth muscle actin+ GFP+ myofibroblasts were generated from GFP+ corneal stromal fibroblasts when GFP- bone marrow-derived cells were present and more alpha smooth muscle actin+ GFP+ myofibroblasts were generated from GFP+ bone marrow-derived cells when GFP- corneal stromal fibroblasts were present. Polyclonal anti-human latency associated peptide (LAP) (transforming growth factor-β1) neutralizing antibody (a-LAP) and/or transforming growth factor-β type I receptor kinase inhibitor (LY-364947) inhibited the generation of alpha smooth muscle actin+ myofibroblasts from either precursor cell in Transwell System co-culture experiments. These data suggest that TGFβ is a paracrine modulator that regulates the generation of myofibroblasts from either corneal fibroblasts or bone marrow-derived cell precursors.

Substratum topography modulates corneal fibroblast to myofibroblast transformation

PURPOSE

The transition of corneal fibroblasts to the myofibroblast phenotype is known to be important in wound healing. The purpose of this study was to determine the effect of topographic cues on TGFβ-induced myofibroblast transformation of corneal cells.

METHODS

Rabbit corneal fibroblasts were cultured on nanopatterned surfaces having topographic features of varying sizes. Cells were cultured in media containing TGFβ at concentrations ranging from 0 to 10 ng/mL. RNA and protein were collected from cells cultured on topographically patterned and planar substrates and analyzed for the myofibroblast marker α-smooth muscle actin (αSMA) and Smad7 expression by quantitative real time PCR. Western blot and immunocytochemistry analysis for αSMA were also performed.

RESULTS

Cells grown on patterned surfaces demonstrated significantly reduced levels of αSMA (P < 0.002) compared with planar surfaces when exposed to TGFβ; the greatest reduction was seen on the 1400 nm surface. Smad7 mRNA expression was significantly greater on all patterned surfaces exposed to TGFβ (P < 0.002), whereas cells grown on planar surfaces showed equal or reduced levels of Smad7. Western blot analysis and αSMA immunocytochemical staining demonstrated reduced transition to the myofibroblast phenotype on the 1400 nm surface when compared with cells on a planar surface.

CONCLUSIONS

These data demonstrate that nanoscale topographic features modulate TGFβ-induced myofibroblast differentiation and αSMA expression, possibly through upregulation of Smad7. It is therefore proposed that in the wound environment, native nanotopographic cues assist in stabilizing the keratocyte/fibroblast phenotype while pathologic microenvironmental alterations may be permissive for increased myofibroblast differentiation and the development of fibrosis and corneal haze.

Interleukin-1 receptor role in the viability of corneal myofibroblasts

The purpose of this study was to investigate the role of interleukin-1 (IL-1) in modulating myofibroblast viability in mouse corneas with stromal opacity. Twenty-four female B6; 129S1-Il1r1tm1Roml/J homozygous IL-1RI knockout mice and 24 control B6129SF2/J mice were included in this study. Each mouse had opacity-generating irregular phototherapeutic keratectomy (PTK) performed with an excimer laser in one eye. Groups of 8 mice from each group were euthanized at one month, three months and six months after surgery and the eyes cryo-preserved. The contralateral eye served as unwounded control. Immunohistochemistry was performed for α-smooth muscle actin (SMA) in central sections of all corneas. The TUNEL assay for apoptosis was performed on 8 sections of four eyes from each group. No SMA+ cells were detected in the stroma of unwounded control or knockout corneas. SMA+ myofibroblast density was significantly higher (p < 0.001) in the IL-1RI knockout group than in the control group at one month, three and six months after irregular PTK. Mean TUNEL+ stromal cells in the anterior 50 μm of stroma was significantly lower in the IL-1RI knockout group compared to the control group at six months after irregular PTK (p = 0.04). These results corroborate the findings of recent in vitro work that demonstrated an antagonistic effect of TGFβ and IL-1 on myofibroblast viability, and found that IL-1-triggered myofibroblast apoptosis was suppressed by TGFβ. Thus, IL-1 is an important modulator of myofibroblast viability during corneal wound healing.

Efficacy and safety of suberoylanilide hydroxamic acid (Vorinostat) in the treatment of canine corneal fibrosis

OBJECTIVE

Study aims were to evaluate the safety and efficacy of the Food and Drug Administration-approved drug Vorinostat [suberoylanilide hydroxamic acid (SAHA)] in the treatment of canine corneal fibrosis using an in vitro model.

METHODS

Healthy donor canine corneas were collected and used to generate primary canine corneal fibroblasts (CCFs) by growing cultures in minimal essential medium supplemented with 10% fetal bovine serum. Canine corneal myofibroblasts, used as a model for corneal fibrosis, were produced by growing CCF cultures in serum-free medium containing transforming growth factor β1 (1 ng/mL). Trypan blue exclusion assays were used to determine the optimal SAHA dose for this in vitro model. Four hour after culturing with TGFβ1, CCF cultures were treated with 0.06% SAHA for 5 min (group 1) and for 24 h (group 2), representing single and multiple dose treatment regimes, respectively. Cultures were then further incubated in the presence of TGFβ1 (1 ng/μL) under serum-free conditions until they reached 70% confluence. Trypan blue exclusion, immunocytochemistry, and TUNEL assays were used to evaluate the cytotoxicity of SAHA. Real-time PCR, western blot analysis, and immunocytochemistry were used to determine the efficacy of SAHA to inhibit canine corneal myofibroblast formation.

RESULTS

Topical SAHA application in both treatment groups successfully decreased α-smooth muscle actin expression when compared to the TGFβ1 only treatment group (P < 0.05). Tested SAHA did not affect CCF phenotype or cellular viability and did not cause significant cell death.

CONCLUSIONS

Suberoylanilide hydroxamic acid safely and effectively inhibits TGFβ1-induced CCFs transformation to myofibroblast in vitro.

Electrophilic PPARγ ligands inhibit corneal fibroblast to myofibroblast differentiation in vitro: a potentially novel therapy for corneal scarring

A critical component of corneal scarring is the TGFβ-induced differentiation of corneal keratocytes into myofibroblasts. Inhibitors of this differentiation are potentially therapeutic for corneal scarring. In this study, we tested the relative effectiveness and mechanisms of action of two electrophilic peroxisome proliferator-activated receptor gamma (PPARγ) ligands: cyano-3,12-dioxolean-1,9-dien-28-oic acid-methyl ester (CDDO-Me) and 15-deoxy-Δ(-12,14)-prostaglandin J(2) (15d-PGJ(2)) for inhibiting TGFβ-induced myofibroblast differentiation in vitro. TGFβ was used to induce myofibroblast differentiation in cultured, primary human corneal fibroblasts. CDDO-Me and 15d-PGJ(2) were added to cultures to test their ability to inhibit this process. Myofibroblast differentiation was assessed by measuring the expression of myofibroblast-specific proteins (αSMA, collagen I, and fibronectin) and mRNA (αSMA and collagen III). The role of PPARγ in the inhibition of myofibroblast differentiation by these agents was tested in genetically and pharmacologically manipulated cells. Finally, we assayed the importance of electrophilicity in the actions of these agents on TGFβ-induced αSMA expression via Western blotting and immunofluorescence. Both electrophilic PPARγ ligands (CDDO-Me and 15d-PGJ(2)) potently inhibited TGFβ-induced myofibroblast differentiation, but PPARγ was only partially required for inhibition of myofibroblast differentiation by either agent. Electrophilic PPARγ ligands were able to inhibit myofibroblast differentiation more potently than non-electrophilic PPARγ ligands, suggesting an important role of electrophilicity in this process. CDDO-Me and 15d-PGJ(2) are strong inhibitors of TGFβ-induced corneal fibroblast to myofibroblast differentiation in vitro, suggesting this class of agents as potential novel therapies for corneal scarring warranting further study in pre-clinical animal models.

Sphere formation from corneal keratocytes and phenotype specific markers

The keratocytes are specialized mesenchymal cells that produce and maintain the extracellular matrix of the corneal stroma. With a typical dendritic and flattened appearance, these cells can morph into fibroblasts and myofibroblasts upon injury, and produce abnormal or fibrotic extracellular matrices detrimental to corneal transparency. Insights into mechanisms that regulate these phenotypic switches and optimal culture conditions that preserve the keratocyte phenotype are important for tissue engineering of the corneal stroma. Like other cell types with self-renewing capacity, keratocytes can form spheres in culture. Here we investigated human and bovine keratocytes with respect to their sphere forming capabilities, and sought to identify potentially distinguishing markers for the keratocyte and fibroblast phenotypes. Keratocytes, isolated from bovine and human corneas, cultured in serum-free medium supplemented with insulin, selenium and transferrin, assumed typical keratocyte morphology, converted to fibroblasts in serum-containing medium and reverted to keratocytes after serum-deprivation. The bovine keratocytes produced spheres under adherent or low attachment conditions, while the human keratocytes produced spheres under low attachment conditions only. The primary keratocytes and fibroblasts expressed vimentin, confirming their mesenchymal origin. Keratocan, considered to be a marker for keratocytes, was also detected in early passage bovine fibroblasts. BMP3 was expressed in keratocytes and keratocyte-derived spheres, while cadherin 5 in keratocytes only, suggesting these as potential keratocyte markers.

Effect of TGFβ and PDGF-B blockade on corneal myofibroblast development in mice

The purpose of this study was to investigate the role of transforming growth factor beta (TGFβ) and/or platelet-derived growth factor-B (PDGF-B) blockade on the differentiation of vimentin and alpha-smooth muscle actin (αSMA)-expressing myofibroblasts associated with haze in mice. Mouse corneas had haze-generating irregular PTK (phototherapeutic keratectomy) and topical treatment with the vectors. Six study groups of PTK treated corneas, with four corneas per group in each experiment, were Group 1) treated with TGFβ-KDEL vector interfering with TGFβ signaling through anomalous sorting of cytokine bound to the expressed altered receptor; Group 2) treated with PDGF-B-KDEL vector interfering with PDGF signaling through anomalous sorting of cytokine bound to the expressed altered receptor; Group 3) treated with both TGFβ-KDEL vector and PDGF-B-KDEL vector to interfere with signaling of both cytokines; Group 4) empty pGFPC1 vector; Group 5) empty pCMV vector; and Group 6) no vector treatment control. At one month after surgery, the corneas were analyzed by immunocytochemistry (IHC) for central stromal cells expressing myofibroblast markers vimentin and αSMA. The stroma of corneas treated with the TGFβ-KDEL vector alone (p < 0.05) or both the TGFβ-KDEL and PDGF-B-KDEL vectors (P < 0.05) had significantly lower density of vimentin-positive cells compared to the corresponding control group. The central stroma of corneas treated with the TGFβ-KDEL vector (p < 0.05) or the PDGF-B-KDEL vector (p < 0.05) had lower density of αSMA-positive cells compared to the corresponding control group. The density of αSMA-positive stromal cells was also significantly lower (p < 0.05) when both the TGFβ-KDEL and PDGF-B-KDEL and vectors were applied together compared to the corresponding control groups. This study provides in situ evidence that TGFβ and PDGF-B have important roles in modulating myofibroblast generation in the mouse cornea after haze-associated injury.

Monocyte development inhibitor PRM-151 decreases corneal myofibroblast generation in rabbits

This study investigated whether PRM-151 (Promedior, Inc., Malvern, PA), a recombinant form of human pentraxin-2 (PTX-2, also referred to as serum amyloid P, hSAP), that inhibits differentiation of circulating monocytes into fibrocytes and profibrotic macrophages, could modulate generation of myofibroblasts after opacity-producing corneal injury in rabbits, and, therefore, have potential to reduce or prevent haze after PRK. Nine diopter PRK for myopia was performed with the VISX S4 IR laser. Four groups of 6 animals were treated in masked fashion: Group 1: 30 μl of topical PRM-151 (20 mg/ml) 6 times a day for 5 days; Group 2: 30 μl topical vehicle 6 times a day for 5 days; Group 3: 200 μl sub-conjunctival PRM-151 (total injection of 4 mg) immediately after surgery and every other day until day 8; Group 4: 200 μl sub-conjunctival injections of vehicle according to the same schedule as group 3. At one month after PRK, the animals were euthanized and immunohistochemistry was performed for the myofibroblast marker α-smooth muscle actin (SMA). The density of SMA+ cells/400× field in the central stroma was determined in each cornea. Myofibroblast density at one month after surgery was significantly lower (p = 0.006) after sub-conjunctival PRM-151 treatment (5.8 ± 2.8 cells/400× stromal field) compared to sub-conjunctival vehicle treatment (15.3 ± 2.9 cells/400× stromal field). There was no significant (p = 0.27) decrease in stromal myofibroblasts triggered by topical PRM-151 treatment (11.8 ± 6.6 cells/400× stromal field) compared to the topical vehicle treatment (14.2.8 ± 6.2 cells/400× stromal field). PRM-151 inhibits myofibroblast generation when administered by sub-conjunctival injection, but not when administered topically, after opacity-producing corneal injury. This study provides additional confirmation that bone marrow-derived cells contribute to corneal myofibroblast generation.

Femtosecond laser in-situ keratomileusis flap configurations

PURPOSE OF REVIEW

The corneal flap laser in-situ keratomileusis (LASIK) is among the most important determinants in the successful outcome of the surgery. Femtosecond lasers have evolved over the last decade to all but replace the mechanical microkeratome as the preferred method to create these flaps. With improvements in femtosecond laser technology, there has been a reduction in the time taken for the cut and the quality of the stromal bed has improved. Improved predictability has led surgeons to explore the possibility of thin flap LASIK.

RECENT FINDINGS

Corneal flaps created with the femtosecond laser have been shown to be more predictable in depth and have a more desirable planar morphology. Corneal flaps created by the femtosecond laser can be customized according to depth, profile, morphology, and side-cut configuration. Changes in the angulation of the side cut, to reduce the incidence of epithelial ingrowth, have not been corroborated by clinical evidence as yet. Thin flap LASIK, also referred to as sub-Bowman's keratomileusis, has the advantage of preserving more stroma and potentially reducing the incidence of corneal ectasia but seems to be associated with an increased incidence of interface haze.

SUMMARY

This review examines the advantages of creating a flap with the femtosecond laser and the various configurations of these flaps. It also explores the advantages of varying the thickness and profile of femtosecond flaps.

Applications of aptamers in nanodelivery systems in cancer, eye and inflammatory diseases

Aptamers are an interesting class of molecules that have potential in many facets of human health. They are characterized by high affinity and specificity to their targets, are small in size, have similar properties to antibodies, but are made synthetically. All of these properties, among others, give aptamers the potential to diagnose, image and treat like no other molecules. By combining the unique properties of aptamers with the ever expanding field of nanotechnology and all it has to offer, we are entering a very promising new area of targeted nanodelivery treatments. These treatments have found success in the complex disease processes of cancer, eye and inflammatory diseases.