Learn how to prepare, store lamellar corneal grafts

Khon Kaen, Thailand-A study of a new approach to preparation and storage of posterior lamellar corneal grafts for transplantation has demonstrated that centralized harvest, cold storage, and shipment by airmail result in viable grafts 2 days later, according to Olan Suwan-apichon, MD, assistant professor, department of ophthalmology, faculty of medicine, Khon Kaen University, Khon Kaen, Thailand.

Dr. Suwan-apichon, who was a research fellow in cornea and refractive surgery at Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, while the study was carried out, collaborated with colleagues at several sites to investigate the new procedure.

According to Dr. Suwan-apichon, the current, standard surgical procedure for corneal transplant is full-thickness penetrating keratoplasty, while the newer lamellar keratoplasty technique is based on the principle of replacing only the diseased portion of the cornea. His laboratory has focused on developing both mechanical and femtosecond laser microkeratome-based techniques for lamellar grafting.

Comparison of keratome cuts

He and his colleagues compared a mechanical microkeratome (Moria LSK-One) and a femtosecond laser microkeratome (IntraLase) in the deep lamellar dissections of donor corneas. The corneas were obtained from the Central Florida Eye Bank in Tampa and shipped to a study site in North Carolina for dissection.

Investigators used 10 corneoscleral buttons, stored in Optisol GS, with an endothelial cell count of more than 2,500 cells/mm2 . Five corneas were dissected with the mechanical microkeratome (Group 1), and five with the femtosecond laser (Group 2). The intended lamellar depth was 350 µm.

In Group 1, the sections were separated immediately using the microkeratome, while those in Group 2 were manually separated 2 days later.

All corneas were stored in Optisol and sealed in original eye bank containers before being shipped by 2-day express delivery service to Wilmer Eye Institute. Upon arrival, they were separated into anterior and posterior grafts. Pachymetry, endothelial viability, and histology were assessed after 48 hours.

"Total corneal thicknesses before microkeratome and femtosecond laser dissection were the same, and after dissection the anterior graft and posterior graft thicknesses in Groups 1 and 2 were the same," Dr. Suwan-apichon said. "This means that the harvested lamellar grafts in each group had the same thicknesses by both techniques."

In Group 1, which had been cut with the mechanical microkeratome, changes in lamellar thickness were observed between day 0 and day 2.

"On day 2, there appeared to be significant thinning of the anterior grafts, in contrast to significant swelling of posterior grafts," Dr. Suwan-apichon said. The devitalized endothelial cells were minimal, with no difference between groups.

"In the femtosecond laser group, we chose not to separate the sections until day 2 in order to reduce the exposure time of stromal surfaces to medium and limit the induced swelling," he said. "We found that the laser device did not show significant difference from the steel blade instrument in terms of accuracy and reproducibility after the 2-day post-dissection storage period.

"In the mechanical microkeratome group, the significant thinning of the anterior graft and the significant swelling of the posterior graft that we found are in agreement with previous reports, which helps demonstrate that the rate of anterior stromal swelling is slower than that of the posterior stroma," Dr. Suwan-apichon said.

The average total corneal thickness increased similarly by the end of the study period using both microkeratomes.