A future with clear vision?

Presbytes, there’s hope; inlays are almost in reach for US patients.

By Martin L. Fox, MD

Since time immemorial men and women have struggled with the often-sudden onset of losing their ability to see closely. It was Aristotle who termed afflicted individuals as presbytes, coining for the ages the term that describes the condition of the aging eye. In man’s early years, having wealth was some help: Romans designated literate slaves to read for them. In the search for a solution innovation was pivotal: Ben Franklin figured out the aging eye couldn’t quite focus like it used to, and invented the bifocal.

Presbyopia affects more than 25% of the world population, claiming more than 1 billion new presbytes annually. It is a condition that virtually all primates face in their fourth or fifth decade.¹ So, the pursuit of a solution for this most universal of human afflictions has become a passion for some refractive surgeons and those in related industry. The search has led to a litany of procedures, many of which have fallen far short on safety and efficacy metrics.

The KAMRA inlay makes use of small aperture optics to address near vision tasks at near and intermediate ranges.

The search could end sooner than later. In August, an FDA panel decided the benefits of the KAMRA (AcuFocus Irvine, Calif.) inlay outweighed the “risks for patients suffering vision loss” because of presbyopia,² pushing it along the approval process. The KAMRA is marketed in 33 countries; the company’s website says 20,000 inlays have been implanted outside of the United States. We may be on the verge of witnessing the birth of a new surgical subspecialty devoted to presbyopia’s effective correction.

Sacrifices and reversibility

Until now, the conventional approach to presbyopia in LASIK and PRK has been limited to monovision or blended vision in which the non-dominant eye is targeted for a myopic goal to allow for midrange near-vision. With a well-motivated patient this approach has provided for reasonable function; however, it does sacrifice distance clarity for a small amount of intermediate vision. Reversibility is a key component of this approach.³

Prior to the advent of corneal inlay technology, attempts at presbyopia correction have included two excimer laser PresbyLasik procedures^(4,5,6); an intrastromal femtosecond laser treatment (IntraCor, Technolas Perfect Vision, Munich, Germany); and two procedures involving expansion of the circumlental space through scleral modification (LaserACE System, ACE Vision Group) and PresView scleral implant (Refocus Group).

While PresbyLasik investigators reported success using central reading and peripheral reading zone excimer techniques, these multifocal laser ablations ultimately created higher order aberration and, consequently, quality of vision issues. Some patients have found it difficult to adapt to the compromise, and others were dissatisfied by the minor loss of distance vision.⁷ Despite this, multifocal excimer designers have not given up on this approach.

The KAMRA inlay is implanted in a femtosecond laser pocket at 200 microns.

The intrastromal femtosecond (IntraCor) approach works via the concentric rings designed to create a multifocal cornea.⁸ Despite favorable outcomes, researchers also have noted a loss of up to two lines of best-corrected vision in 7.1% of eyes; reversibility of the effect and quality of vision remain issues.^9,10

Scleral expansion procedures

While the LaserACE and PresView implant procedures have been demonstrated to produce credible clinical results, improvement in near-vision in both procedures remains, for the most part, transient and unpredictable for most study patients. Device modifications and trials continue; phase 3 clinical trials have begun for both.^11,12,13

The path to clear vision has been anything but straight, but one that has served a purpose. Surgeons now realize the required procedural caveats for success. Jeff Machat, MD, and his associate, Sondra Black, OD, of Crystal Clear Vision in Toronto, who have been implanting KAMRA for the past two years, say those caveats are clear. Effective successful presbysurgery must be:

1) Extra ocular

2) Have the preservation of quality distance vision while improving function at intermediate- and near-distance

3) Should not require perpetual enhancement or revision and

4) The technology must have reversibility.

They view the KAMRA inlay as meeting all criteria. Their belief in KAMRA is so complete that both have had the inlay implanted into their own eyes.

Corneal presbyopia inlays

This implantable corneal inlay is perhaps the most exciting of the new technologies in the US presbyopia-correction market. Inlay development has required years to address requisite safety factors including sizing, biocompatibility, adequate permeability to allow nutrient distribution and appropriate depth in the cornea. Inlays may be implanted in smooth femtosecond laser created pockets or under LASIK flaps; they require femtosecond lasers to produce adequate bed smoothness.

Pocket techniques are viewed as superior in corneal inlay surgery as they allow for maintenance of structural integrity, avoid issues of flap striation and preserve corneal nerve health, allowing for quicker healing and visual recovery. The placement of inlays requires specialized, precise attention to centration and depth of placement. New technologies that can produce and confirm accurate inlay placement in this critical area are essential for successful surgery.

Small-aperture optics

KAMRA is novel in presbyopia treatment, making use of small-aperture optics producing an increase in depth of focus, thereby preserving distance acuity while improving near and intermediate visual function. At 5 microns thick, the KAMRA is 3.8 mm in diameter and annular in shape with a central 1.6-mm aperture that is designed for corneal pocket implantation at a depth of 200 microns concentric to the line of vision.

The inlay is made from a propriety polyvinylidene fluoride material with 8400 laser etched 5.5-11.5 micron micro perforations placed in a random array to assure permeability. Unlike other inlay technology, the KAMRA continuously compensates for the progression loss of accommodative amplitude by means of improvement of depth of focus with its small aperture optics.

Jeff Machat, MD, and his associate, Sondra Black, OD, of Crystal Clear Vision in Toronto.

Seyeddain et al¹⁴ confirmed two-year data on the KAMRA inlay implanted in 32 eyes and confirmed that 96.9% of patients read J3 or better in the implanted eye with mean binocular UCNA improvement from J6 preoperatively to J1 after 24 months. Mean binocular uncorrected intermediate visual acuity was 20/20 at 1 month and remained 20/20 throughout 24-month follow-up and mean UCDA of 20/20 in the implanted eye and 20/16 binocularly. Company results presented to the FDA showed that 87% of enrollees were able to see 20/40 or better at near at 36 months post-op with 54% seeing 20/25 or better and 29% at 20/20 following the same period of follow-up with good overall satisfaction and preservation of good distance acuity. Initial symptoms of glare and dryness were reported to diminish over the first 12 months of observation.¹⁵

Newer kids on the block

Beside KAMRA, three other corneal inlays are under investigation: Raindrop Inlay (Revision Optics), the Flexivue Microlens (Presbia) and Icolens (Neoptics AG).

The Raindrop is a permeable 2 mm clear biocompatible hydrogel that works as a space-occupying lens designed for placement under a LASIK flap at a depth of 120 to 130 microns in the nondominant eye. The lenticule improves near and intermediate vision by creating steepening surface curvature change resulting in a multifocal cornea.

The Flexivue Microlens and the most recent inlay entry Icolens¹⁶ are multifocal pocket inlays designed to produce corneal multifocality in the nondominant eye. Flexivue is recruiting participants for a Phase 3 trial.¹⁷

Treating the presbyopic patient

Providing the presbyopic patient with functional, safe and lasting vision could be a reality soon. That written, the process of creating successful outcomes will rely on careful selection of candidates, exquisitely performed surgery and a comprehensive approach towards management of patient expectations. Drs. Machat and Black say their success with the KAMRA inlay has come only with great attention to detail, an evolving learning curve and a comprehensive approach to postsurgical counseling and management. OM

REFERENCES

About the Author
	Dr. Martin L. Fox is medical director at the Cornea and Refractive Surgery Practice of New York and at Clarity Refractive Services of West Orange, New Jersey. E-mail him at foxmd@laserfox.com or by phone 917-207-3147. His website is www.laserfox.com. Disclosure: Dr. Fox reports that he has no financial interests with any of the companies or manufacturers mentioned in this article.