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July 2007

Size and Location of Corneal Rotational Autografts

Arch Ophthalmol. 2007;125(7):992. doi:10.1001/archopht.125.7.992-a

I enjoyed the article by Afshari et al1 on the optimal size and location for corneal rotational autografts using a simplified mathematical model and would like to note that the article confirms previous studies on mathematical models for the calculation of the size and location of corneal autografts.2-5 In these previous investigations, the equation for the optimal trephine diameter was diameter(trephine) = [¾ × diameter(cornea)] − [½ × e], with e being the preoperative distance between the corneal center and the nearest edge of the opacity covering the corneal center.4 The postoperative diameter of the optical zone was [2 × diameter(trephine)] − diameter(cornea). A postoperative clear optical zone of half of the corneal diameter was achieved if the opacity just touched but did not extend beyond the corneal center. For a postoperative optical zone of at least 30% and 40% of the corneal diameter, the opacity should preoperatively not extend beyond the corneal center for more than 20% and 10%, respectively, of the corneal diameter. The advantage of this equation of the previous study4 is that it includes the diameter of the cornea. It may be clinically useful to take the corneal diameter into account because rotational corneal autografts have been performed for young children with relatively small corneas as well as for adults with normal-sized or even oversized corneas.5 Assuringly, all of the equations cited show the same result if the corneal diameter is assumed to be 11 mm: the optimal diameter of the trephine would be 8 mm.2,4

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