Considering trephination

The way in which donor corneal buttons are trephinated could impact transplant outcomes Source: Edward J. Holland, M.D.

The style of corneal donor button trephination could be an additional consideration in optimizing transplant outcomes. A study, published in the November 2009 issue of Current Eye Research, suggests that certain trephination approaches produce more irregular margins than others and also more endothelial cell loss—facts that should not get lost in the surgical shuffle. “A significant amount of endothelial cell density decline has been attributed to intraoperative damage at the peripheral margin of the graft and host,” according to lead study author Majid Moshirfar, M.D., John A. Moran Eye Center, University of Utah, Salt Lake City. “Trephination is an additional source of cell loss, likely due to trauma from manipulation during the preparation process and from the trephination itself.”
Three methods of trephination compared

To that end, Dr. Moshirfar compared three methods of trephination: trephination with a standard posterior punch, vacuum posterior punch, and vacuum trephine and artificial anterior chamber system (completed with microcorneal scissors). Twelve corneal specimens were produced with each method and by the same surgeon. “On specular microscopic examination, there was more preservation of endothelial cell density centrally following trephination with the standard and vacuum posterior punches compared to the anterior chamber and vacuum trephine system,” Dr. Moshirfar reported. “There was slightly more loss associated with the vacuum trephine than the standard punch, although this finding was not statistically significant.”
Specifically, central endothelial cell loss (cells/mm2) after trephination was –14.0 ± 49.9 for the standard punch, –85.6 ± 87.0 for the vacuum punch, and –116.0 ± 223.1 for the vacuum trephine and artificial anterior chamber system.
Dr. Moshirfar cited more mechanical trauma arising from the use of corneal scissors and greater tissue manipulation as the reasons for more endothelial cell loss with the vacuum trephine/artificial anterior chamber system method. The appearance of the corneal buttons was also better with the standard and vacuum punch approaches. “The buttons created by both the standard and vacuum posterior punches created a more uniform and outward sloping edge,” Dr. Moshirfar reported. “The margin following anterior trephination had a more ragged appearance and an inward slope.”
Again, Dr. Moshirfar suggested corneal scissors may be to blame for the ragged cuts. “Another consideration is that the inward sloping nature at the edge of anteriorly trephinated buttons may result in less endothelial cells available for transplantation,” Dr. Moshirfar reported. “Posterior cut buttons contain a larger area of endothelium than those cut anteriorly because the diameter of Descemet’s membrane on the button is equal to the diameter of the trephine itself. This is not the case for anteriorly approached trephinations, where the inward slope at the margin ensures that the endothelial surface will be a slightly smaller circumference and surface area than the intended trephine size.”
The researchers also found the standard and vacuum punch methods to be fast and easy to use. “In contrast, the anterior approach was more time consuming and required more tissue manipulation,” Dr. Moshirfar reported. “In addition, it was somewhat difficult to ensure that all of the air bubbles were removed from the anterior chamber before trephination.” Changes in the anterior technique could lead to improvements in endothelial cell retention, Dr. Moshirfar suggested. “For instance, if a diamond blade were to be used to complete the trephination, rather than corneal scissors, the results might be different,” Dr. Moshirfar noted. “In addition, while preparing buttons using the anterior chamber system, the authors recommend grasping the outer edge of the corneo-scleral rim during manual incision with microscissors in efforts to minimize manipulation of the eventual donor button.”
Meanwhile, Sujatha Mohan, M.D., associate medical director, Rajan Eye Care Hospital, Chennai, India, agreed that the manner in which donor corneal buttons are trephinated affects the outcomes of surgery. Handheld trephines tend to create donor corneas that slope outward, she said. “The position might not be perfect with that,” she said. “It might induce a bit of astigmatism. Wound healing might also be slightly altered.”
The vacuum method is reasonably better, she said. “The vacuum hold on to the cornea in a better way,” she said. “The trephine goes down in a vertical fashion. But the handheld trephine cannot achieve verticality.” Because the cornea is curved, the handheld trephine cannot cut as precisely as the cornea should be cut to achieve optimal results. Dr. Mohan said she still uses handheld trephination frequently because the cost is less, and in India, cost is an important factor. That said, since long-lasting quality of life is important to younger patients with keratoconus and dystrophies, Dr. Mohan said she prefers to use a vacuum trephine in such patients to maximize outcomes without inducing astigmatism.

Editors’ note: Dr. Moshirfar has no financial interests related to this study. Dr. Mohan has no financial interests related to her comments.

Contact information

Mohan: +91 044 2834 0500, rajaneye@md2.vsnl.net.in
Moshirfar: majid.moshirfar@hsc.utah.edu