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Implantation of a synthetic intracorneal inlay has been associated with a history of failure when explored as a refractive surgical procedure.
"All we have to do is consider the great progress made in the aircraft industry since the beginning of the 20th century to realize that perseverance pays," said Dr. Alio, professor and chairman, Department of Ophthalmology, Miguel Hernández University, and medical director, Vissum Alicante, Alicante, Spain.
"It is important for researchers developing intracorneal inlays to keep trying," Dr. Alio said. "Based on better knowledge of corneal anatomy, better implant technology, and better surgical tools, we are seeing better results with more recent investigational devices."
Providing a brief history of intracorneal inlays, Dr. Alio noted that Jose Barraquer, MD, PhD, pioneered this area beginning in 1949, but the flint glass material he used originally led to problems with corneal edema, neovascular ingrowth, and necrosis.
The modern era of intracorneal inlays involving hydrogel materials began more than 20 years later, but the early hydrogel devices also suffered because of biotolerance problems. Beginning in the late 1970s and into the early 1980s, a number of other materials were also studied but without success because of issues with corneal anatomy, histology, metabolism, material biotolerance, and optical performance.
"This experience taught researchers that the cornea is not as simple a tissue as it seems to be," Dr. Alio said.
A review of published literature of the past two decades showed only 10 published papers reporting on five different biomaterials and including only four clinical studies. Most of the published scientific evidence involves hydrogel inlays, but those papers describe different types of inlays implanted with different surgical techniques.
The papers published over the past decade include several from Dr. Alio and colleagues that showed acceptable to good predictability and visual outcomes using a hydrogel corneal inlay in eyes where the device could be maintained. However, a variety of problems led to explanation of more than half of the devices with a mean survival time of only 37.5 months as calculated by Kaplan-Meier analysis.
Optical performance was the leading cause for explantation during the early postoperative period (less than 6 months) and was related primarily to centration issues that led to irregular topography with induction of coma and spherical aberrations that were incompatible with good vision. In addition, despite evidence of material biotolerance from preclinical studies, biocompatibility was an issue.
"After months to years postimplantation, there was development of scarring and opacities with confocal evidence of epithelioid cells and activated keratocytes in the interface," Dr. Alio said. "Even after explantation, we have never determined the origin of the epithelioid cells.
"However, this experience also proved that the implants could be explanted and that the haze would eventually disappear," he added.