Corneal trephining for penetrating keratoplasty.

MANY complications following corneal grafting procedures may be attributed to the technical and biological problems associated with this type of surgery. It is generally agreed that accurate apposition of the graft to the margin of the incision in the recipient cornea is of the greatest importance. Manual trephining for penetrating keratoplasty frequently results in badly cut grafts, and for this reason many modifications of the simple Elliot trephine have been made. Mechanically driven trephines have been used by Castroviejo (1941) and Green (1945). Ptinch devices have been employed by Wiener and Alvis (1940), Clark (1954), and Pittar (1954). Other special techniques have been devised by Amsler and Verrey (1948) and Franceschetti (1955) to reduce the discrepancy between the shape of the graft removed from the donor eye and the place prepared for it in the recipient. These techniques have not been widely accepted, however, and Stansbury (1949) states that " considering that the much-to-be-desired complete incision is not likely to be obtained with any of the more complicated instruments yet devised, the simplicity of the manual trephine warrants its further employment ". Michaelson (19M4) describes the variation in the bevel of the graft and recipient bed which occurs when trephining is performed under conditions of altered intra-ocular pressure. A high pressure increases the corneal curvature, so that when the elasticity of the graft restores the curvature to normal the internal diameter of the disk is greater than the external diameter (Fig. 1). Thus the bevel of a graft cut under high pressure slopes outwards, and conversely, when the pressure is low, it will slope inwards. Therefore, to perfect a technique of corneal trephining, not only must a complete disk be obtained, but also one whose bevel is constant.