Stromal haze, myofibroblasts, and surface irregularity after PRK

Abstract

The aim of this study was to investigate the relationship between the level of stromal surface irregularity after photorefractive keratectomy (PRK) and myofibroblast generation along with the development of corneal haze.Variable levels of stromal surface irregularity were generated in rabbit corneas by positioning a fine mesh screen in the path of excimer laser during ablation for a variable percentage of the terminal pulses of the treatment for myopia that does not otherwise generate significant opacity. Ninety-six rabbits were divided into eight groups:Slit lamp analysis and haze grading were performed in all groups. Rabbits were sacrificed at 4 hr or 4 weeks after surgery and histochemical analysis was performed on corneas for apoptosis (TUNEL assay), myofibroblast marker alpha-smooth muscle actin (SMA), and integrin α4 to delineate the epithelial basement membrane.Slit-lamp grading revealed severe haze formation in corneas in groups IV and VI, with significantly less haze in groups II, III, and VII and insignificant haze compared with the unwounded control in groups I and V. Analysis of SMA staining at 4 weeks after surgery, the approximate peak of haze formation in rabbits, revealed low myofibroblast formation in group I (1.2 ± 0.2 cells/400× field) and group V (1.8 ± 0.4), with significantly more in groups II (3.5 ± 1.8), III (6.8 ± 1.6), VII (7.9 ± 3.8), IV (12.4 ± 4.2) and VI (14.6 ± 5.1). The screened groups were significantly different from each other (p <0.05), with myofibroblast generation increasing with higher surface irregularity in the −4.5 diopter PRK groups. The −9.0 diopter PRK group VI had significantly more myofibroblast generation than the −9.0 diopter PRK with PTK-smoothing group VII (p <0.01). Areas of basement membrane disruption were demonstrated by staining corneas for integrin α4 and were prominent in corneas with grade I or higher haze. SMA-positive myofibroblasts tended to be present sub-adjacent to basement membrane defects. Late apoptosis was detected at 1 month after surgery within clusters of myofibroblasts in the sub-epithelial stroma. In conclusion, these results demonstrated a relationship between the level of corneal haze formation after PRK and the level of stromal surface irregularity. PTK-smoothing with methylcellulose was an effective method to reduce stromal surface irregularity and decreased both haze and associated myofibroblast density. We hypothesize that stromal surface irregularity after PRK for high myopia results in defective basement membrane regeneration and increased epithelium-derived TGFβ signalling to the stroma that increases myofibroblast generation. Late apoptosis appears to have a role in the disappearance of myofibroblasts and haze over time.

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

“…According to these studies, the disruption of the epithelial basement membrane correlates with the differentiation of myofibroblasts due to the release of transforming growth factor beta-1 [31] followed by myofibroblast-expressed SMA. Although the damage caused to the basement membrane in the incision for ICRS implantation is small, we also found ∝−SMA-positive cells around the segment, although there were fewer than after other procedures, such as phototherapeutic keratectomy [32] and PRK [39]. These cells were α-SMA-positive from one month to three months, which correlated with the appearance of haze around the segment, as reported in other studies [23,40,41].…”

Fibroblast-derived 3D matrix differentially regulates the growth and drug-responsiveness of human cancer cells

“…Hence, although these matrices may regulate tumor cell growth, any observed effect is not necessarily comparable to that produced by a fibroblast-rich stroma. Moreover, a plethora of reports have suggested that the thinning or degradation of basement membranes at early stages of tumor development is a frequent event (Akashi et al, 2005;Capo-Chichi et al, 2002;Netto et al, 2006). This early basement membrane degradation facilitates a more direct contact between the neoplastic epithelial cells and the adjacent mesenchymal compartments.…”

Intraocular straylight before and after low myopic photorefractive keratectomy with and without mitomycin C

“…During corneal wound healing, most patients experience transient changes in corneal transparency (9) . Injury to the epithelium and removal of the central epithelial basement membrane, which also occur in PRK, initiate a complex sequence of events mediated by Intraocular straylight before and after low myopic photorefractive keratectomy with and without mitomycin C epithelial-stromal interactions (10,11) . Corneal fibroblast and myofibroblast generation, in addition to changes in the quality and quantity of extracellular matrix, are the main alterations contributing to stromal opacity following PRK surgery (9,12) .…”