Regeneration of the human corneal endothelium

The ability of the human corneal endothelium to regenerate is studied with the scanning electron microscope through examples of corneal diseases and penetrating keratoplasties. This study does not lead to final conclusions on the possibilities of regeneration of the human corneal endothelium but allows us to say that:

regeneration occurs through size increasing and deformation of the remaining cells.

the increase in number and size of surface microvilli may simply indicate a state of cell activation.

the présence of two nuclei in one cell is probably obtained by amitotic division but no complete mitosis has been seen.

Displacement of endothelial cells is a real progression and the cell is able to overcome obstacles.

the fibroblastic transformation of the endothelial cells is present in man but this may simply represent the migrating form of the cells.

     

Deep lamellar keratoplasty by deep parenchyma detachment from the corneal limbs

AIM: To improve the deep lamellar keratoplasty technique. METHOD: For the easy and reliable perfomance of deep lamellar keratoplasty (DLKP), detachment of Descemet's membrane through the corneal limber flap was improved. To expose Descemet's membrane, the parenchyma was detached by hydrodelamination through a sclerocorneal flap made in the corneal limbs. The parenchyma was removed after the pseudochamber between it and Descemet's membrane was maintained with viscoelastic material. The corneal graft was placed with a running suture. 22 eyes were treated. RESULTS: Complete exposure of Descemet's membrane was obtained in 20 of the 22 eyes (91%). The membrane was perforated in five of the 22 eyes (23%) during surgery, and two of the 22 eyes (9%) were converted to penetrating keratoplasty. These two eyes developed keratoconus after acute corneal hydrops. CONCLUSION: Compared with the conventional procedure, this new method provides easy, reliable exposure of Descemet's membrane.     

Regeneration of the corneal endothelium in the rabbit--preliminary trials--I

It has been demonstrated in a long-term experiment that the corneal endothelium of the rabbit is capable of repairing severe mechanical lesions several times. The more severe the lesion, the longer it takes to heal. The endothelium "broke down" for the first time after the sixth endothelial lesion was inflicted and so on after the tenth, eleventh and twelfth endothelial lesion. The regeneration time was prolonged considerably. Sometimes a "restitutio ad integrum" occurs and the cornea clarifies; sometimes one sees a retrocorneal membrane, which can also lead to clarification of the cornea. Plastic platelets implanted in addition (PVAL or HEMA copolymers) do not influence the time required for regeneration of the endothelium. In other tests these plastics proved to be nontoxic to the endothelium.     

Regeneration of corneal epithelial basement membrane following thermal cauterization.

Thermal cauterization of the corneas of nine rhesus monkeys was performed by multiple thermokeratophore applications at temperatures of 90 degrees or 120 degrees C. Significant clinical observations included the resteepening of corneal curvature, delayed epithelial healing, stromal haze or scarring, and peripheral neovascularization. Reestablishment of tight adhesion of the regenerated epithelium to Bowman's layer required approximately 6 weeks. By transmission and scanning electron microscopy, the original basement membrane seemed relatively intact immediately following cauterization but disappeared within 1 week. The regeneration of new basement membrane complexes began at 1 week with the appearance of short discontinuous segments of basement material with hemidesmosomes and similarly required approximately 6 weeks for complete restoration.     

Regeneration of cat corneal endothelium induced in vivo by fibroblast growth factor

The corneal endothelium of man, primates and carnivores has limited regenerative ability. Fibroblast growth factor (FGF) stimulates the proliferation of various mesoderm-derived cells, including corneal endothelial cells, in vitro. In the present work the effect of FGF on the regeneration of injured cat endothelium in vivo was studied. Scraping of cat corneal endothelium off Descemet's membrane was carried out by a specially designed instrument. FGF from crude preparations (25 micrograms in 50 microliter saline) or affinity purified FGF (0.5 micrograms in 25 microliter saline) were injected immediately after the scraping of the endothelium, and in both cases significant stimulation of endothelium regeneration was observed. During the first 2 weeks after scraping, the endothelial cell density (ECD) in FGF-treated eyes was higher by a factor of 1.7-2.3 than that in the control eyes. This marked difference decreased with time, but even after 12 weeks the ECD in FGF-treated eyes was higher by a factor of 1.15-1.30 than in the control eyes. Furthermore, FGF improved the polygonal shape of the cells and decreased the corneal thickness. These results clearly demonstrate the efficacy of FGF in inducing the proliferation of cat corneal endothelial cells in vivo and indicate its potential application in clinical practice.