Tissue evaluation

After the corneoscleral rim come in to the cornea bank and after the storage but before the transportation to the operation the cornea is evaluated by an inverted light microscope.
The stroma and endothelium are examined very carefully the microscopic appearance of a normal endothelium, the cells are all nearly the same size and shape with no abnormal dark or bright structures present and no evidence of inflammatory cells or adherent debris. The number of cells is estimated with help of a calibrated grid in the ocular. The cell density has to higher than 2000 cell/mm2.
Each examination is recorded in digital pictures on PC.

The following criteria for acceptance are adopted:

1. Minimally 2000 cells/mm2 before and after preservation.
2. After preservation the presence, number, and location of cells stained by trypan blue are recorded. If there are more than 1% stained (dead) cells present after preservation, the corneas are discarded
3. A regular cell mosaic (no significant polymegathism, or pleomorphism).
4. Folds caused by the swelling during preservation covered with endothelium.
5. Clear-cut cell borders and a smooth appearance.
6. Maximum cell loss of 10% during storage

The age of the donor seems to be of secondary consideration, and suitable corneas from older donors that have passed the microscopic criteria have provided excellent grafts.

An older cornea with a high cell density, low polymegathism or pleomorphism, and a normal appearance is probably functionally superior to a younger cornea that does not meet the evaluation criteria.