Rotational corneal keratoplasty (ipsilateral rotational corneal autograft) is a long-time back described technique for a salvage of eyes with corneal scars. Described in abandunce in Pubmed, this technique involves placement of clear cornea in front of the pupil instead of previous scar via simple rotation and suturing.
Again, earlier there were plenty of methods to calculate the size of the graft (and therefore – corneal trephine) needed. Today, with a help of computers, there is no place for formulas. Photoshop or analogues will do it for you very nicely (and it was described in research well before). For these pictures I used freely distributed GIMP software.