The optical axis is marked with a fine-tipped gentian violet surgical marking pen. This should be over the pupillary axis unless previous trauma, surgery or inflammation has distorted the pupil. The pupil is often centered just nasal to the anatomic center of the cornea, a fact which may be useful when corneal opacification prevents visualization of the pupil. It may be necessary to decenter the graft slightly to encompass pathology. Mild decentration can usually be well-tolerated, but markedly decentered grafts result in high astigmatism and may increase the risk of graft rejection if near the limbus.
The principal meridians are marked at the limbus with a radial marker. This step may help in proper suture alignment, particularly if there is significant scleral collapse and wound deformity after trephination. In this case, an 8-line marker was used.
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