25 Jan 2017
Femtosecond and excimer lasers ensure economic manufacture and precise shaping.Allotex and 3D-Micromac recently announced a cooperative agreement to develop and market a laser system for shaping corneal grafts manufactured from human donor corneas, offering clinicians and patients a route to overcoming the biocompatibility problems that can detrimentally affect corneal implants at present.
David Muller, CEO of Allotex - and previously of vision-correction companies Summit Technology and Avedro - said that the partners will work together to apply 3D-Micromac's laser micromachining expertise to Allotex's development of natural collagen lenses, and produce a laser system suitable for marketing to ophthalmologists and ophthalmic clinics.
The principle behind corneal implants, either as inlays positioned at the center of the cornea or as onlays located just under the outer layer, has been known for some 70 years, along with the idea of using them to change the shape of the cornea and correct certain sight deficiencies.
Unlike LASIK and similar refractive surgeries which remove tissue from the eye, corneal implants change the shape of the cornea through the addition of a carefully shaped piece of material, machined to match the patient's vision requirements. This offers a potentially attractive route to treating presbyopia, the natural loss of focusing power than comes with age.
"LASIK has become less popular for treatment of myopia and underperforms as a means to cure hyperopia, which has spurred consideration of corneal implants as an alternative surgical approach for vision disorders," commented Muller. "In particular, corneal implants have been developed as a means to treat prebyopia, but the missing link until now has been a way to reduce issues of biocompatibility for these implants, and make the implantation both safe and predictable."
Three distinct corneal inlays for presbyopia are currently available or at various stages of commercialization - from AcuFocus, Presbia, and ReVision Optics, based on hydrogels or suitable hydrophilic acrylic materials. But biocompatibility issues remain an issue, according to Muller.
"The cornea is very intolerant of foreign bodies, and although developers have worked hard to make their product more biocompatible there are still limitations," he said. "Any implant will affect the dynamics of both oxygen flow and nutrient supply, even if it is made very small, and patients typically require topical steroids over long periods of time to stabilize the implant."
Hence the appeal of an implant made not from a hydrogel but from an authentic biological tissue, removing biocompatibility as a complication altogether. As it happens, the cornea is one of the sites in the body that have "immune privilege," and can accept tissue grafts with little or no risk of rejection and no requirement for tissue matching. So Allotex intends to manufacture implants from donor human corneas, machined to the correct shape and dimensions by a laser micromachining operation.
Excimer and femtosecond sources
"Advances in several technologies have come together to make corneal tissue addition a viable option, including developments in laser technology," commented Muller. "The Allotex approach uses a femtosecond laser to delaminate the donor cornea into a number of individual lamina, as raw material used to form the implants. This is a key economic factor: the ability to take a human cornea, slice it into 25 sheets, and then cut a number of blanks from each sheet allows you to obtain 150 to 200 treatments from a single donated cornea, and Allotex has proprietary IP in this area."
Excimer lasers are then used to sculpt the individual corneal tissues into the right profiles to meet patients' individual requirements, an area where 3D-Micromac's expertise in micromachining comes into play.
A third crucial factor in the Allotex plan is recent advances in long-term tissue storage, or eyebanking, without which the corneal tissues would have a natural shelf-life measured in days. Allotex's eyebank partner employs an e-beam sterilization technique which enables the donor tissues to remain sterile for up to two years at room temperature - another key economic advantage, allowing tissues to be kept in stock until needed.
Having worked together on the project for 18 months before the recent formalized announcement, Allotex and 3D-Micromac anticipate the first prototype laser system being delivered to the Allotex facility in Zurich in approximately one month's time, with a second system due to be delivered to the company's US operation around 2 months later. After commissioning, the intention is for clinical trails to commence in Q3 2017 and commercialization to follow in late 2018.
Muller foresees the system coming ro market via two distinct business models, suitable for different clinics' needs. One model involves clinics having the laser system on-site and producing the corneal lenticules on the premises, while the other is for the clinic to examine the patient and then order the required item from Allotex. The latter model might better suit the greater complexity of prescriptions for hyperopia and myopia, and the former could suit presbyopia patients - effectively analogous to the patient buying a pair of reading glasses off the shelf.
"We feel this is a unique opportunity, not least because the learning curve is so shallow," said Muller. "The basic procedure is familiar to clinicians, and we find most ophthalmologists have a story to tell about how they have tried a similar procedure before but found that it didn't work because of the materials involved. Now we have set the stage for what we anticipate will be a highly successful commercial roll-out of our technology."
About the Author
Tim Hayes is a contributor to Optics.org.