[Endothelial evaluation of corneal transplants by digital imaging]

Evaluation of corneal graft endothelium in organ culture comprises judgement of cell area, cell form and cell density by phase contrast microscopy after cell border swelling in hypotonic solution. Up to now, cell density has been determined via counting cells by hand within a fixed frame on polaroid images regarding the magnification factor. It was the purpose of this paper to establish a facilitated and reliable method for endothelial cell count by digital imaging and to compare it with our standard procedure of endothelial cell count by hand.

After cell border swelling in hypotonic solution endothelial images are recorded by a digital camera that is connected to a computer system where the grey scale images are processed into binary images using specialized enhancement and thresholding techniques. A fuzzy logic based computer program was developed in order to differentiate between single and multiple objects, i.e. living and necrotic cells. This digital imaging system determines endothelial cell density automatically and offers the possibility to correct the data in any case of misinterpretation. Twenty corneal grafts were evaluated with this system by two experienced investigators and the results were compared with endothelial cell count by hand.

Using the new system, intra- and interindividual variability of endothelial cell count was statistically significantly lower compared with evaluation by hand. Furthermore, less time for evaluation and documentation was necessary.

In a reduced period of time endothelial cell density of corneal grafts in organ culture can be determined reliably and reproducibly with the new digital imaging system if the possibility of data correction is used in case of misinterpretation. In the future, the necessity of corrections should be reduced and the use of multiple fixed frames should further improve quality control of corneal grafts.