Corneal inlays play increasing role in presbyopia

As the number of LASIK procedures being performed continues to fall worldwide, correction of presbyopia is receiving increasing attention as being the final frontier and “holy grail” for refractive surgery, said Wayne Crewe-Brown, MD, at Refractive Surgery 2017.

Current surgical methods for presbyopia correction include corneal refractive surgeries to create either monovision or blended monovision, refractive lens exchange, and corneal inlays.
While none of these techniques is perfect, corneal inlays have several advantages.

Looking ahead, allogenic corneal inlays are an exciting development for bringing a better solution, said Dr. Crewe-Brown, consultant ophthalmic surgeon, London.

“Based on my clinical experience to date, the minimally invasive nature of corneal inlays and of the pending onlays combined with their removability means they will play an ever-increasing role in our practices for the correction of presbyopia,” he said.

Understanding the market

Dr. Crewe-Brown noted that the presbyopic population is the fastest-growing demographic globally. By 2020, it is projected that there will be 2.1 billion presbyopes in the world, and a significant portion of these individuals have disposable income.

Among the current surgical methods for presbyopia correction, an important limitation of corneal refractive monovision is that more than 30% of patients cannot adapt to having a different refraction in fellow eyes. An issue for refractive lens exchange is that younger presbyopes may balk at the idea of having an invasive intraocular procedure.

Inlay options

In 2017, there are three commercially available inlays, each working by a different mechanism. They include the Microlens (Presbia), which is a refractive optic and still pending FDA approval; the Raindrop (ReVision Optics), which acts by reshaping the cornea; and the KAMRA inlay (AcuFocus), a small-aperture device.

Dr. Crewe-Brown noted that in addition to being removable, the advantages of corneal inlays include preservation of options for future presbyopic correction.

In addition, they not only provide for good near and intermediate vision, but they also perform better than the alternatives for better preserving distance vision, Dr. Crewe-Brown said.

“I have implanted thousands of KAMRA inlays and about 350 Microlens inlays, and I have also done thousands of corneal refractive monovision procedures,” he said. “There is  no doubt that my inlay patients have better distance vision.”

In photopic conditions, patients who have inlays also maintain stereoacuity that is similar to normal binocular vision, and that contributes to good patient satisfaction.

In addition, inlays can be combined with other refractive surgeries and with cataract procedures.

“The so-called ‘plano presbyope’ is a very rare breed, and the bulk of my inlay surgeries have been combined with LASIK or PRK,” Dr. Crewe-Brown said.

The available inlays are not free of limitations. Dr. Crewe-Brown said that the black annulus of the KAMRA has been a rare cosmetic complaint of patients with light colored irides.

“The ring is hardly noticeable in someone with a dark iris, but in my practice I see a lot of blue-eyed patients in whom it can be visible,” he said.

As another issue, because they are made of a synthetic material, all corneal inlays carry a risk of biocompatibility issues.

“We have to acknowledge the critics and skeptics of the inlays who say that the cornea is not a place for a foreign body,” Dr. Crewe-Brown said.

Allogenic solutions

The idea for a presbyopic allogenic inlay is not new. Rather, it was introduced by José Barraquer, MD, in 1949 through his experiments with epikeraotphakia/keratophakia. However, its development was impeded by predictability and economic issues.

Recent technological developments are making allogenic corneal inlays much more viable.
“Advancees in laser technology allow for more accurate ways to sculpt the donor tissue and there have also been developments in tissue banking procedures that improve the availability viability of donor corneal tissue,” Dr. Crewe-Brown said.

The sources for allogenic corneal inlays that are being explored include the lenticule removed during a SMILE procedure and donor cornea obtained from tissue banks. Soosan Jacob, MD, Agarwal’s Eye Hospital, Chennai, India, is developing use of the SMILE lenticule in a procedure known as PEARL (PrEsbyopic Allogenic Refractive Lenticule).

Also in this area, Allotex, a startup company established in 2014, is developing human corneal allograft inlays and onlays. Dr. Crewe-Brown quoted Vance Thompson, MD, who has been involved in the project as saying he is excited about the Allotex allograft tissue, which combines learnings from decades of corneal inlay research and technology development with the pristine biocompatibility of human collagen.

“Dr. Thompson is a very experienced and respected colleague in this field, and he sees a great future in the allograft inlay,” Dr. Crewe-Brown said.

Current decisions

For patients who are interested in an inlay, Dr. Crewe-Brown said there is no exact science for choosing among the available options.

“It comes down to a combination of factors, including assessment of dry eye and pupil size, being sure of what patients want and what they need to suit their lifestyle, and then choosing accordingly,” he said.

Dr. Crewe-Brown receives financial assistance for travel and accommodations from AcuFocus and Presbia.