Presbyopia — the loss of accommodation of the crystalline lens with age — is a normal aging process that affects us all, typically in the fifth decade of life. The resulting deterioration in near vision is treated with corrective lenses, but surgical alternatives have long been an area of extensive research.
Strategies to treat presbyopia include monovision, multifocality, extended depth of focus, and restoration of accommodation. Until recently, surgical options were limited to corneal refractive procedures and intraocular lens implants. Corneal inlays of various designs have been investigated for years and two different ones are now FDA approved. Future treatments that are still being researched include newer presbyopic correcting IOLs, scleral expansion bands, and topical medication (miotic that does not cause cycloplegia). This article is an update on the status of presbyopic corneal implants.
All About Corneal Inlays
For decades, ophthalmologists have attempted refractive procedures by inserting various materials and lenses into the cornea. Intracorneal implants are thin contact lens-like devices that can be placed under a corneal flap. The patient’s refractive error can be altered by changing the shape or power of the cornea without removing tissue.
Similar to intracorneal ring segments (Intacs), the advantage of corneal inlays is that the procedure is adjustable as well as reversible by exchanging or explanting the inlay if necessary. However, inserting a foreign body in the cornea has potential risks. In addition to infection and complications in creating corneal flaps and pockets, implant decentration or extrusion can occur. There is generally a loss of uncorrected distance visual acuity (UCDVA) of one line in the eye with the implant. Furthermore, necrosis of the stromal tissue overlying the implant has been a significant concern, and the long-term effects of intracorneal devices are unknown. Thus, historically there has been limited success with corneal inlay procedures until the most recent generation of corneal implants were developed.
There are three different types of corneal implants — the KAMRA® Inlay (AcuFocus), the Raindrop® Near Vision Inlay (ReVision Optics), and the Flexivue Microlens™ (Presbia). These implants are small synthetic discs that are placed in the central cornea of an individual’s nondominant eye, either under a flap or within a pocket created by a femtosecond laser. They have all demonstrated efficacy in improving near and intermediate visual acuity; however, the implants can cause some glare and do reduce uncorrected distance vision by approximately one line in the operated eye. An advantage over other presbyopic surgical treatments is that the corneal implant procedure is reversible.
Below is a summary of the three corneal inlays:
KAMRA Inlay (AcuFocus)
- Mechanism of Action: extended depth of focus with the pinhole effect
- Material: polyvinylidene difluoride
- Design: 5 microns thick opaque disc with 3.8 mm outer diameter and 1.6 mm central opening, and 8400 micro-perforations (5-11 microns in size) to allow nutrient flow through the implant
- Indication: treatment of presbyopia in emmetropic (spherical equivalent of +0.50 to -0.75 D, less than or equal to 0.75 D of astigmatism), presbyopic (add of +1.00 to +2.50 D) patients 45-60 years of age
- Technique: placed in deep stromal pocket at least 200 microns or greater than 40% depth of the total corneal thickness (reduced risk of haze); requires special equipment: femtosecond laser approved for corneal stromal pocket creation, and a device for measuring centration (Acutarget HD analyzer)
- Results: pivotal data (508 patients at 24 sites) demonstrated UCNVA of 20/40 or better in 83.5% of patients at 12 months and 87.2% of patients at 24 months, three-line average gain in UCNVA (20/60 to 20/30), and minimal change in UCDVA; however, there was some decrease in contrast sensitivity in the implanted eye, 10% of patients did not gain two lines of UCNVA and also lost more than one line of UCDVA, and the inlay was removed in 45 (8.5%) patients.
- Status: FDA approved April 2015
Raindrop Near Vision Inlay (ReVision Optics)
- Mechanism of Action: create multifocal cornea by changing corneal shape (central steepening)
- Material: hydrogel (allows nutrients to pass directly through the inlay)
- Design: hyperprolate-shaped clear inlay with no refractive power, 2 mm wide and 32 microns thick centrally
- Indication: treatment of presbyopia in emmetropic (spherical equivalent of +1.00 to -0.50 D, presbyopic patients 41-65 years of age
- Technique: placed under a LASIK flap or in a 150 micron depth corneal pocket
- Results: pivotal data (373 patients at 11 sites) showed UCNVA of 20/40 or better in 98% of patients and 20/25 or better in 93% of patients at 12 months, five-line average gain in UCNVA, 2.5 line average gain in UCIVA, and 1.2 line average loss in UCDVA. Refractive stability was achieved at 6 months, there was no loss of contrast sensitivity, and 11 implants (2.9%) were removed.
- Status: FDA approved June 2016
Flexivue Microlens (Presbia)
- Mechanism of Action: create multifocal cornea by changing corneal power to create slight myopia and monovision
- Material: hydrophilic acrylic
- Indication: treatment of presbyopia
- Design: central plano zone with ring of peripheral refractive power ranging from +1.25 to +3.5D, 3 mm diameter, 15 microns thick, and 0.15 mm central opening to allow nutrients to flow through the lens
- Results: six month FDA trial data (421 patients) reveals a five-line average gain of UCNVA (20/80 to 20/25) in the treated eye and a decrease in UCDVA.
- Status: CE Mark December 2009; FDA trials
Promising Procedure
Currently in the United States, corneal inlays are the most promising refractive procedure for the treatment of presbyopia. This technology is minimally invasive, corneal tissue sparing, safe, effective, and reversible.
However, potential adverse events such as fibrosis and deposits still remain a concern for the long-term tolerability of these implants. In addition, UCNVA in presbyopic, middle aged patients will continue to deteriorate over time as these individuals become increasingly more presbyopic and also develop cataracts and shifts in their refractive error. The opaque Kamra inlay has the issues of cosmesis, perfect centration, and reduced contrast sensitivity as well.
This is an exciting time for presbyopia treatment, and it will be interesting to see which technology emerges as the favored one.