Corneal inlays and corneal onlays are small lenses or other optical devices that are inserted into the cornea to improve reading vision. A few of these devices resemble very small contact lenses.
The primary purpose of these devices is to enhance near vision and decrease the requirement for checking out glasses in older adults who have presbyopia.
As their names recommend, corneal inlays and onlays differ in where they are implanted within the cornea: corneal onlays are put near the surface of the eye, directly under the thin outer layer of the cornea called the epithelium; inlays are put deeper in the cornea – in the thicker middle layer called the stroma.
Since they are implanted deeper in the cornea, corneal inlays might be more stable and deliver more predictable and long-lasting outcomes than corneal onlays. For these factors, it appears corneal inlays will likely be the preferred device for physicians and patients thinking about this refractive surgery choice.
Corneal inlay surgery in some cases can be combined with LASIK surgery to fix both presbyopia and nearsightedness, farsightedness and/or astigmatism. (This is thought about an “off-label” use of the procedure in the United States, meaning the U.S. Food and Drug Administration (FDA) will permit an eye surgeon to perform the combined procedure, even though it has not yet been formally authorized by the FDA.)
Corneal inlay surgery is less invasive and may have fewer risks than phakic IOL procedures, which include implanting lenses further back inside the eye, either straight behind or in front of the pupil.
Likewise, since no corneal tissue is removed during inlay surgery, this procedure may be a good alternative for people whose corneas are too thin for LASIK or PRK.
Kamra Corneal Inlay Review
In April 2015, the Kamra inlay became the first corneal inlay to get FDA approval for use in vision correction surgery carried out in the United States. Developed by AcuFocus, the Kamra inlay also is commercially available in almost 50 nations worldwide.
The Kamra inlay is designed to decrease or get rid of the need for checking out glasses amongst people in between the ages of 45 and 60 who have good distance vision without glasses however have problems seeing up close due to presbyopia.
The Kamra inlay is really small and thin – it’s simply 3.8 mm in diameter (about one-quarter the size of a soft contact lens) and 6 microns thick (less than one-tenth the density of a typical human hair, or about the diameter of a single red cell).
The inlay has an opaque external ring and a tiny (1.6 mm diameter) main opening. When implanted in the cornea, the Kamra inlay is positioned so its central opening is directly in front of the pupil of the eye. This produces a “pinhole video camera effect,” which expands the variety of clear vision to bring near items into sharper focus while keeping clear range vision.
The Kamra inlay generally is implanted in the non-dominant eye. This enables both eyes to see at distance, while the Kamra inlay improves near vision.
The procedure takes less than 15 minutes and can be carried out in the eye surgeon’s workplace. Healing time might vary from individual to individual. No stitches are needed.
Raindrop Near Vision Inlay
The Raindrop Near Vision Inlay, established by Revision Optics, acquired FDA approval in June 2016 for presbyopia surgery performed in the United States.
Formerly referred to as PresbyLens in the United States and Vue+ in Europe, the tiny (2.0 mm size) clear inlay is made from medical-grade hydrogel plastic just like that used for soft contact lenses and has optical characteristics that are practically similar to the human cornea, according to the company.
The Raindrop Near Vision Inlay is implanted in the patient’s non-dominant eye through a laser-cut flap in the cornea. When in position, the inlay alters the curvature of the cornea so the front of the eye acts similar to a multifocal contact lens.
In a research study of 38 people (ages 45 to 56) who went through the Raindrop Near Vision Inlay procedure:
- Six months after receiving the implant, many people might perform near vision tasks such as checking out a paper without the requirement for eyeglasses.
- Most topics also did not need spectacles for intermediate tasks such as reading a computer screen.
- All study participants had 20/25 or better distance vision in both eyes.
- Only one negative event was reported, when an inlay had to be rearranged.
FDA approval of the Raindrop Near Vision Inlay was based upon the results of a large medical trial of 373 patients who underwent the implant procedure. Two years after surgery, 92 percent of individuals had actually uncorrected near visual skill of 20/40 or much better, which typically is more than appropriate to read paper and publication print without glasses.
Presbia Flexivue Microlens for Presbyopia
Another ingenious corneal inlay designed for the correction of presbyopia is the Presbia Flexivue Microlens, being developed by Ireland-based Presbia PLC. This device looks like a small bifocal intraocular lens like those used in cataract surgery. It measures just 3.2 mm in diameter and is available in a variety of powers, depending on the patient’s near vision needs.
During the Presbia Flexivue Microlens procedure, little pocket is produced in the corneal stroma with a femtosecond laser, and the inlay is inserted into this pocket with an unique device. The pocket seals itself, and the entire procedure typically takes less than 10 minutes.
The corneal inlay can be eliminated and changed with a higher or lower power lens if needed.
The Presbia Flexivue Microlens is not yet FDA-approved for use in the United States, however it has gotten a CE mark for the European Economic Area.
In a 2012 study, patients in Italy and Greece who went through the Flexivue Microlens procedure reported very high satisfaction rates one year after implantation, with 97 percent saying their uncorrected near vision in the implanted eye was either good or excellent, and 97 percent reporting that their uncorrected range vision with both eyes open was either good or exceptional.
A clinical trial needed for approval of the Presbia Flexivue Microlens in the United States started in 2014.
Corneal Onlays
Corneal onlays resemble corneal inlays, however are designed to be put closer to the front surface area of the cornea, just under the external layer called the epithelium.
The corneal epithelium consists of about 10 percent of the overall density of the cornea and functions as a protective barrier to keep bacteria, dust and other foreign compounds from permeating the eye. The epithelium also soaks up oxygen and nutrients from the tear film so they can nourish the remainder of the cornea.
Though some research in establishing corneal onlays is continuous in Europe, it appears that corneal inlays have ended up being the preferred technology for corneal implants developed for vision correction, inning accordance with W. Bruce Jackson, MD, professor and chairman of ophthalmology at the University of Ottawa (Canada) and one of the early investigators of corneal onlays.