Bruce C. Roberts

A new paradigm for corneal wound healing research: The white leghorn chicken (Gallus gallus domesticus)

Purpose. To evaluate the chicken cornea as a model for corneal wound healing research. Methods. We conducted studies on normal chicken corneas and on corneas following mechanical debridement and photorefractive keratectomy (PRK). Results. The chicken cornea possesses six distinct layers that resemble the layers of the human cornea, including a substantial Bowman’s layer measuring 5.2 ± 0.3µm thick. Reepithelialization time was 44.8 ± 1.1 hours with a sliding rate of 75.3 ± 3.2µm/hour following mechanical debridement and 54.4 ± 2.8 hours with a sliding rate of 63.3 ± 3.2µm/hour for PRK-treated corneas. Biomicroscopic haze post-PRK peaked at 4–6 weeks and regressed until 20 weeks post-PRK. Histologic and clinical observations of wound healing strongly paralleled that noted in humans. Conclusion. The chicken cornea’s morphology and wound healing response render it a useful model for corneal wound healing investigations.

Effect of hydrostatic pressure gradients and Na2EDTA on permeability of human Schlemm's canal cell monolayers.

PURPOSE Elevated intraocular pressure in those with glaucoma appears to be a function of increased resistance to movement of aqueous humor through the conventional outflow pathway. The majority of resistance in both normal and glaucomatous eyes is generated in the region between the juxtacanalicular trabecular meshwork and the inner wall of Schlemms canal. To accommodate transient elevations in pressure, we hypothesize that conventional outflow increases rapidly due to changes in complexity of intercellular junctions between cells of the inner wall of Schlemms canal. METHODS To test this hypothesis we examined specifically the effects of hydrostatic pressure gradients and the calcium chelator, Na2EDTA, on permeability of cultured human Schlemms canal cell monolayers in isolation. Human Schlemms Canal cells were isolated, cultured and then seeded onto permeable supports and maintained in culture to allow intercellular junctions to mature. With a minimum net transendothelial electrical resistance of 10 Ohm cm2, cells were placed into an Ussing-type chamber and hydraulic conductivity was calculated from pressure and flow measurements that were continuously recorded. Simultaneously, transendothelial electrical resistance was measured manually at fixed intervals. In parallel experiments, cell margins were monitored in real time by videomicroscopy. RESULTS During the baseline measurement period when cells were exposed to pressure but not Na2EDTA, hydraulic conductivity was constant but transendothelial electrical resistance decreased continuously at rate of 0.24 Ohm cm2/minute. After Na2EDTA treatment, no significant change in transendothelial electrical resistance was measured while, hydraulic conductivity of Schlemms Canal monolayers increased significantly by 125%; corresponding to noticeable intercellular separations. Restoration of cell-cell contact was observed by videomicroscopy 30 minutes following washout of Na2EDTA and functionally after 2 hours. CONCLUSIONS Responses of Schlemms Canal cells to pressure and calcium chelators in vitro are consistent with a role for calcium sensitive junctions in outflow resistance in vivo.