NTERIOR SEGMENT Refractive Surgery
WHAT’S UP, DOC?
Investigating the effects of ectasia after LASIK and SMILE for SMILE Xtra and LASIK Xtra5. Thus, the team investigated if CXL could help protect the cornea after undergoing these procedures.
Careful Hops to a (Studied) Conclusion
This isn’t exactly what we meant when we said “Rabbit Model”...
by Joanna Lee
L
aser-assisted in-situ keratomileusis (LASIK) has come a long way since Jose I. Barraquer Moner first tried to reshape the cornea with a stromal sculpting method in 1948. In 1990, the use of a microkeratome opened the doors to make the contemporary LASIK surgery a reality.1 Today, the latest method in refractive surgery is SMILE or small incision lenticule extraction. During the procedure, an intrastromal lenticule is created with a femtosecond laser; and compared to LASIK, SMILE has shown to better preserve the biomechanical structures of the eye postoperatively. That’s because LASIK’s vertical cut (to create the flap) increases the risk of structurally weakening the cornea2 – and it’s this weakening that exposes the cornea to ectasia.
Recently, a team in Singapore investigated the effects of ectasia in the cornea after LASIK and SMILE. The goal was to find out if SMILE would result in less ectasia compared to LASIK, as detailed in their paper “Corneal stability of LASIK and SMILE when combined with collagen cross-linking”, published in Translational Vision Science & Technology3. Another objective of the study was to look at one of the latest techniques – collagen cross-linking (CXL), which has been noted to stop the progression of keratocconus4 when the procedure is done together with SMILE or LASIK, also known as SMILE Xtra and LASIK Xtra. Although there has not been much evidence of concomitant CXL’s benefit on the structure of the cornea, there has been, however, emerging support
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December/January 2020
Corresponding researcher of this investigation, Dr. Jod Mehta from Singapore National Eye Centre, shared how they used a rabbit model to induce ectasia. “Corneal ectasia is a weakening or protrusion of the cornea due to biomechanical weaknesses,” said Dr. Mehta. According to him, ectasia is caused primarily by keratoconus, while the secondary type of ectasia sometimes arises after LASIK or refractive surgeries. “Previous studies have shown that it is the vertical incision in the cornea, such as after-flap creation, that weakens the cornea the most – hence causing ectasia. With SMILE, the vertical incision is much smaller than after LASIK, therefore SMILE does not prevent ectasia, but it may reduce it. However, this requires more evidence,” he continued.
What the Rabbits Taught Us “We used a rabbit model to induce ectasia by removing a lot of stroma tissue,” shared Dr. Mehta. Fourteen rabbits were involved in the experiment in accordance to ethical guidelines. The team compared the occurrence of ectasia between LASIK and SMILE treatments and also looked at the effects of concomitant CXL. The rabbits were divided into 4 groups: SMILE, SMILE Xtra, LASIK and LASIK Xtra. Save for one rabbit which had corneal infection, 6 eyes underwent SMILE, while SMILE Xtra was performed
