Early wound healing of laser in situ keratomileusis-like flaps after treatment with human corneal stromal stem cells.

PURPOSE: To use a well-established organ culture model to investigate the effects of corneal stromal stem cells on the optical and biomechanical properties of corneal wounds after laser in situ keratomileusis (LASIK)-like flap creation. SETTING: School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom. DESIGN: Experimental study. METHODS: The LASIK-like flaps were produced in sheep corneas. The flap beds were treated with corneal stromal stem cells and were then replaced and allowed to heal for different periods of up to 3 weeks in organ culture. The optical transmission of the cornea, the force required to detach the flap, and the presence of myofibroblasts near the flap bed were measured. RESULTS: Corneal stromal stem cell-treated flap beds were statistically significantly more transparent after 3 weeks in culture than the untreated controls. At 3 weeks, the mean force necessary to detach the flap was more than twice the force required for the respective control samples. Concurrently, there were 44% activated cells immediately below the flap margin of the controls compared with 29% in the same region of the corneal stromal stem cell-treated flaps. CONCLUSIONS: In this system, the presence of corneal stromal stem cells at the wound margin significantly increased the adherence of LASIK-like flaps while maintaining corneal transparency. It is postulated that this is achieved by the deposition of extracellular connective tissue similar to that found in the normal cornea and by the paucity of activated keratocytes (myofibroblasts), which are known to scatter a significant amount of the incident light. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Correction: Quantification of Collagen Ultrastructure after Penetrating Keratoplasty - Implications for Corneal Biomechanics.

[This corrects the article on p. e68166 in vol. 8.].

Quantification of collagen ultrastructure after penetrating keratoplasty - implications for corneal biomechanics.

PURPOSE: To quantify long-term changes in stromal collagen ultrastructure following penetrating keratoplasty (PK), and evaluate their possible implications for corneal biomechanics. METHODS: A pair of 16 mm post-mortem corneo-scleral buttons was obtained from a patient receiving bilateral penetrating keratoplasty 12 (left)/28 (right) years previously. Small-angle x-ray scattering quantified collagen fibril spacing, diameter and spatial order at 0.5 mm or 0.25 mm intervals along linear scans across the graft margin. Corresponding control data was collected from two corneo-scleral buttons with no history of refractive surgery. Wide-angle x-ray scattering quantified collagen fibril orientation at 0.25 mm (horizontal)×0.25 mm (vertical) intervals across both PK specimens. Quantification of orientation changes in the graft margin were verified by equivalent analysis of data from a 13 year post-operative right PK specimen obtained from a second patient in a previous study, and comparison made with new and published data from normal corneas. RESULTS: Marked changes to normal fibril alignment, in favour of tangentially oriented collagen, were observed around the entire graft margin in all PK specimens. The total number of meridional fibrils in the wound margin was observed to decrease by up to 40%, with the number of tangentially oriented fibrils increasing by up to 46%. As a result, in some locations the number of fibrils aligned parallel to the wound outnumbered those spanning it by up to five times. Localised increases in fibril spacing and diameter, with an accompanying reduction in matrix order, were also evident. CONCLUSIONS: Abnormal collagen fibril size and spatial order within the PK graft margin are indicative of incomplete stromal wound remodelling and the long term persistence of fibrotic scar tissue. Lasting changes in collagen fibril orientation in and around PK wounds may alter corneal biomechanics and compromise the integrity of the graft-host interface in the long term.

An x-ray scattering study into the structural basis of corneal refractive function in an avian model.

Avian vision diseases in which eye growth is compromised are helping to define what governs corneal shape and ultrastructural organization. The highly specific collagen architecture of the main corneal layer, the stroma, is believed to be important for the maintenance of corneal curvature and hence visual quality. Blindness enlarged globe (beg) is a recessively inherited condition of chickens characterized by retinal dystrophy and blindness at hatch, with secondary globe enlargement and loss of corneal curvature by 3-4 months. Here we define corneal ultrastructural changes as the beg eye develops posthatch, using wide-angle x-ray scattering to map collagen fibril orientation across affected corneas at three posthatch time points. The results disclosed alterations in the bulk alignment of corneal collagen in beg chicks compared with age-matched controls. These changes accompanied the eye globe enlargement and corneal flattening observed in affected birds, and were manifested as a progressive loss of circumferential collagen alignment in the peripheral cornea and limbus in birds older than 1 month. Progressive remodeling of peripheral stromal collagen in beg birds posthatch may relate to the morphometric changes exhibited by the disease, likely as an extension of myopia-like scleral remodeling triggered by deprivation of a retinal image.

Adhesion of laser in situ keratomileusis-like flaps in the cornea: Effects of crosslinking, stromal fibroblasts, and cytokine treatment.

PURPOSE: To evaluate 3 approaches, both cellular and acellular, to improve the healing of laser in situ keratomileusis flaps in bovine corneas. SETTING: School of Optometry and Vision Sciences and Cardiff Institute of Tissue Engineering and Repair, Cardiff University, Cardiff, United Kingdom. DESIGN: Experimental study. METHODS: Laser in situ keratomileusis-like flaps were created in bovine corneas, and the flap bed was treated with tumor necrosis factor-α, interleukin-1α, Fas ligand, transforming growth factor-ß(1), or activated stromal fibroblasts. In separate experiments, flaps were created and repositioned. The corneas were then crosslinked using ultraviolet-A (UVA) light. All samples were then placed in organ culture for up to 4 weeks. Untreated samples acted as controls. RESULTS: All treatments increased the adherence of the stromal flap. This was achieved at the expense of corneal clarity except in the case of crosslinking (CXL). In this case, the flap adhesion force immediately increased while the cornea remained clear. The force then decreased gradually during organ culture, although it remained at twice the level of the control corneas after 3 weeks in culture. CONCLUSIONS: The results suggest that riboflavin-UVA CXL is a hopeful approach for increasing the adherence strength of corneal flaps while keeping the cornea clear. Further studies are necessary to confirm the durability of the strengthening effect and to exclude serious late complications. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.