Novel technique facilitates graft preparation

Los Angeles-A modified surgical technique for centering the optical core within the donor graft used in a Boston Type I Keratoprosthesis (Boston KPro) is an easy-to-learn alternative that seems to allow for reproducible centration of the donor assembly, said Neda Shamie, MD.

Dr. Shamie, associate professor of ophthalmology, Doheny Eye Institute, USC Keck School of Medicine, Los Angeles, noted she sought to develop another method for centering the optical core within the donor graft because this step is typically the most unpredictable portion of the surgery. The inspiration came while punching out Christmas cookies. Her approach is to punch the 3.0-mm central core first instead of, per traditional teaching, as the final step.

“I learned the standard technique widely practiced for centering the 3.0-mm optical punch within the 8.5-mm donor disc from my friend and colleague, Anthony Aldave, MD. Considering the challenge of this step and the need to train fellows in an academic practice, I wanted to develop an alternate method that both performed reliably and was transferable,” said Dr. Shamie, who is also medical director, Doheny Center Beverly Hills, Beverly Hills, CA.

“I have been using the modified technique since 2010, and have been able to perform the central punch step with less trepidation, a steady heart rate, and excellent results,” she added. “Furthermore, I think it is easy enough that mentors can delegate the preparation of the donor graft to novice surgeons without any apprehension.”

The Type I Boston KPro is a PMMA device with a collar button design featuring front and back plates that are snapped together with a disc of donor cornea sandwiched between them. Once these three elements are assembled, the front and back plates are fixed together with a titanium locking ring, and the entire unit is transplanted similarly to a corneal graft. In order to allow the front and back plates to fit together, a 3.0-mm hole is trephinated from the center of the graft. Centering of the 3.0-mm punch within the donor cornea is important to avoid optical zone decentration.

“Although there are modifications and surgical techniques that can be used if the central optical core is decentered, there can also be difficulty with wound construction if the posterior plate overhangs the graft edge,” Dr. Shamie said.

The approach developed by Dr. Shamie begins with drying the epithelial surface of the corneal-scleral donor and centering it onto a Barron vacuum donor punch block (Katena Products). Drying of the epithelium is important so that the tissue does not slip in the punch, she noted.

After applying vacuum, the 3.0-mm central button is punched. Because that step often results in loss of vacuum, the tissue is then recentered on the donor punch block using the 3.0-mm opening as a centering guide. Then, suction is reapplied to stabilize the tissue, and the outer punch is performed to create a graft of 8.0 to 9.0 mm in diameter, while centration of the 3.0-mm opening is ensured through direct visualization.

To investigate the accuracy of the new technique for achieving centration of the 3.0-mm opening, Dr. Shamie undertook a laboratory-based study using four corneal discs that had been assigned to research purposes. The corneas, supplies, and facilities were provided by the Lions Eye Bank of Oregon.

After performing the punch, photographs were taken with a digital slit-lamp camera and the images were magnified to pixels and analyzed using PhotoShop software (Adobe). Four different observers measured the distances in pixels from the outer edge of the central punch to the outer boundary of the graft along the horizontal and vertical axes. The diameters of the graft along the 45º and 135º axes were also measured as a control.

The results showed that the 3.0-mm punch was nearly exactly centered. There was only a 1-pixel (0.03 mm) difference in size comparing the two horizontal distances and only a 1.3-pixel difference comparing the vertical distances.

“With only a single ‘technician’ performing the punch in a very small sample size and no controls, this study has several limitations. However, in my hands, it seems to be a consistently accurate and easily transferrable technique of preparing the donor disc for the Boston Type I Keratoprosthesis,” Dr. Shamie said.

Dr. Shamie has no relevant financial disclosures for the material she discussed.

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