In experimental models, posterior lamellar keratoplasty can be performed through a limbal incision and a mid-stromal pocket. The procedure may be a potential alternative in the surgical management of corneal endothelial disorders.

Aim-To analyse the human corneal stroma in extreme hydration to discover if its structure is responsible for corneal stability. Methods-Corneas in several hydration states were used: postmortem control corneas (PM; n=3), corneas left for 1 day in phosphate buVered saline (PBS; n=4), and corneas left for 1 day (n=4), 2 days (n=4), 3 days (n=2), and 4 days (n=4) in deionised water. All corneas were fixed under standardised conditions and processed for light and electron microscopy. In addition, two fresh corneas from the operating theatre were studied which were processed 6 months after storage in sodium cacodylate buVer. Results-After 1 day in deionised water maximal stromal swelling was reached which did not change up to 4 days. The stroma of deionised water corneas (1400 µm) was much thicker than that of PBS corneas (650 µm) and PM corneas (450 µm). Deionised water treatment led to disappearance of all keratocytes leaving only remnants of nuclei and large interlamellar spaces. In these specimens the distance between the collagen fibres had increased significantly, but the diameter of the collagen fibres did not seem to be aVected. A remarkable observation was that the most anterior part of the stroma (100-120 µm) in all deionised water specimens and those stored for 6 months in buVer was not swollen, indicating that the tightly interwoven anterior lamellae are resistant to extreme non-physiological hydration states. Conclusions-The rigidity of the most anterior part of the corneal stroma in extreme hydration states points to an important role in maintenance of corneal curvature. Since a large part of this rigid anterior part of the stroma is either removed (PRK) or intersected (LASIK), it is possible that in the long run patients who underwent refractive surgery may be confronted with optical problems. (Br J Ophthalmol 2001;85:437-443)

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Human corneas were preserved up to 40 days in a modified tissue culture medium at 31 degrees C. The corneal endothelium was examined by light microscopy before and after culture. After staining with trypan-blue the number of dead cells was counted and by swelling of the intercellular borders in a 1.8 per cent sucrose solution the cellular mosaic was observed. A loss of endothelial cells was found varying from 0-30 per cent. During culture the stroma increased considerably in thickness. Prior to transplantation the cornea was thinned during 24 h in culture medium containing 5 per cent Dextran T500. The combination of the organ culture procedure and the evaluation of the endothelium enables preservation of human corneas for at least 30 days. In addition the quality of the endothelium is guaranteed and the transport of corneas can be carried out at room temperature.

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FLEK effectively reduces postoperative astigmatism and results in an absence of wound healing related problems in patients with endothelial disease. However, visual acuity is lower as compared with conventional PK, and the high level of endothelial cell loss warrants a modification of the insertion technique of the endothelial graft.

Background/aims-Povidone-iodine (PVP -I) is applied for microbial decontamination of human eyes donated for transplantation. Concentrations and immersion times vary greatly. The eVectiveness and toxicity of PVP-I were assessed for diVerent decontamination protocols. Methods-Human donor eyes and corneas were immersed in diVerent concentrations (5-100 mg/ml) of PVP-I for diVerent times (2-30 minutes). The penetration of iodine into the corneal tissue was assessed by x ray microanalysis. Microbial contamination was determined by taking cultures of the limbal areas and storage solutions and by incubation of the corneoscleral buttons in antibiotic-free culture medium. Cytotoxicity of PVP-I for corneal fibroblasts in culture was assessed using the MTT assay. Results-Depending on concentration and immersion time iodine was found to penetrate into the epithelium, Bowman's layer, and stroma in amounts equivalent to 2-40 mg/ml PVP-I. The MTT assay demonstrated that 2.5 mg/ml PVP-I caused total damage to fibroblasts in vitro. Rinsing eyes with tap water and subsequent immersion in PVP-I reduced the rate of contamination from 82 out of 106 to 69 out of 106 and 37 out of 106, respectively. Antibiotics in the storage medium further reduced contamination from about 40% to 3%. Microbial contamination was not reduced by increasing the concentration and immersion times beyond 5 mg/ml PVP-I for 2 minutes. Conclusion-Immersion of human donor eyes in 5 mg/ml PVP-I solution for 2 minutes significantly reduces microbial contamination of donor corneas without relevant penetration of iodine into the corneal layers. Higher PVP-I concentrations and longer immersion times do not further reduce contamination, whereas the amount of iodine penetrating the corneal layers is elevated above the level cytotoxic for corneal fibroblasts. In view of this, concentrations above 5 mg/ml of PVP-I and immersion periods over 2 minutes are not recommended for reduction of the contamination rate of donor eyes. (Br J Ophthalmol 1999;83:1019-1026