Presbyopia, the age-related loss of the ability to actively focus on near objects, was known to the ancient Greeks. In fact, it was Aristotle who referred to individuals suffering from difficulty with reading as “presbytes,” coining for the ages the term that describes the condition of the aging eye (Wade, 2000).
Presbyopia is a frustrating yet inescapable visual disability that intellects have been attempting to address since the first glass lenses were introduced in the late 13th century. Benjamin Franklin tackled presbyopia and was credited with the invention of the bifocal lens in 1784. At that time, he wrote a letter to a friend announcing, “if all the other defects and infirmities were as easily and cheaply remedied, it would be worthwhile for friends to live a good deal longer,” (Isaacson, 2005).
Today, presbyopia affects nearly 1.7 billion people worldwide, and that number is expected to soar to 2.1 billion by 2020 (Market Scope, 2012). Despite its ubiquity, the exact mechanism behind presbyopia is not fully understood. Changes in the ciliary body, zonules, lens, and lens capsule are known to play a role. This complexity makes presbyopia the most challenging visual defect to correct.
While the onset of presbyopia is an unavoidable part of aging, its effects can be treated through a variety of both surgical and nonsurgical methods. Corrective lenses have been the mainstay for centuries, but the advent of surgical techniques has drastically altered the typical treatment mindset and has led an ever-increasing portion of our patient population to seek spectacle and contact lens independence.
Patients pursuing surgery do not typically understand the challenges of treating presbyopia. It is important that clinicians have an understanding of the various concessions associated with each procedure so that they may better educate their patients.
The refractive surgery approach to presbyopia in laser vision correction has conventionally been limited to monovision laser-assisted in situ keratomileusis (LASIK), in which the nondominant eye is targeted for a myopic goal to allow for improved near vision. Ideal monovision patients must be able to tolerate visual imperfection, because monovision does sacrifice distance clarity for a small amount of near vision gain. Contrast sensitivity and stereoacuity are significantly diminished (Alarcón et al, 2011).
The results of laser vision correction procedures are not reversible and often need to be enhanced for a greater effect as patients age. Therefore, they are not typically ideal for treating presbyopia (Goldberg, 2001).
Other attempts at presbyopia correction have included two excimer laser presbyLASIK procedures, an intrastromal femtosecond laser treatment, and two procedures involving expansion of the circumlental space through scleral modification and scleral implant (Fox, 2016). While some of these efforts have demonstrated credible clinical results, further investigation is needed for them to receive U.S. Food and Drug Administration (FDA) approval.
Implantable corneal inlays are a newer technology in the presbyopia correction market. With the developments of newer synthetic materials that have improved biocompatibility, better understanding of corneal wound healing, and technological developments with femtosecond laser and stromal pocket creation software, there has been a rekindling of interest in corneal inlays (Srinivasan, 2016).
Currently, the new generation of corneal inlays to improve presbyopia is comprised of three design types based on the mechanism of action: small aperture (Kamra Inlay, AcuFocus, Inc.); corneal reshaping, which does not have intrinsic refractive power but does create a central hyperprolate cornea (Raindrop Near Vision Inlay, ReVision Optics, Inc.); and refractive optic inlays, which provide corneal multifocality (Flexivue Microlens, Presbia Plc). All of these inlays are implanted into the nondominant eye only. Their benefits are that they are potentially reversible, easy to implant, additive, and tissue sparing, and they can be combined with other corneal refractive procedures to correct ametropia (Srinivasan, 2016).
- Kamra Inlay The Kamra inlay was FDA approved in April 2016. It is 6μm thick and 3.8mm in diameter. This biocompatible disc is made from a proprietary polyvinylidene fluoride material and has a 1.6mm central opening that is designed to act as a pinhole to increase patients’ depth of field and improve near vision with little sacrifice in distance acuity. Eight thousand four hundred laser-etched micro-perforations distributed in a pseudorandom pattern prevent diffraction issues at night and assure proper nutrient flow (Waring and Berry, 2013). Unlike other inlay technology, the Kamra continuously compensates for the progressive loss of accommodative amplitude by improving depth of focus with its small aperture optics (Fox, 2016).
- Raindrop Near Vision Inlay In June 2016, the FDA approved the Raindrop inlay. This lenticule is a permeable, 2mm, clear biocompatible hydrogel that works as a space-occupying lens designed for placement under a femtosecond-created LASIK flap. The resulting modification of corneal shape creates a hyperprolate cornea that is steepened over the diameter of the inlay, resulting in multifocality that corrects vision at intermediate and near ranges.
- Flexivue Microlens This corneal inlay is currently under investigation and is pending FDA clearance. It is a multifocal pocket inlay designed to produce corneal multifocality in the nondominant eye. The Flexivue Microlens is a transparent, hydrogel-based, concave-convex lens. The peripheral zone contains the refractive power, ranging from +1.50D to +3.50D in 0.25D increments; the central zone has no power and surrounds a small central hole that facilitates nutrient flow (Whitman, 2016).
Although it is difficult to have a direct head-to-head comparison between these new generations of corneal inlays because of their different mechanisms of action, the surge in the peer-reviewed literature on the short- and medium-term results seems to suggest that these inlays provide good unaided near and intermediate vision with minimal compromise to the unaided distance vision in the eye with the inlay (Srinivasan, 2016).
The options previously described are examples of extraocular solutions. Phakic individuals who have visually significant cataracts with symptomatic presbyopia may instead elect for intraocular surgical correction by cataract removal and intraocular lens (IOL) placement. Currently, there are a few surgical options to correct presbyopia after cataract surgery: IOLs targeted for monovision, accommodative IOLs, multifocal IOLs, and extended depth of focus (EDOF) IOLs (Shiple and Aquavella, 2013).
- Monovision Monovision correction has been available for some time and has previously been reviewed. However, you must discuss anisometropia and reduction of binocular acuity and stereopsis before making this recommendation.
- Accommodative IOLs Accommodating IOLs involve either forward-backward axial movement under ciliary muscle contraction, change in lens thickness, or optic arching. The net effect is a change in focal point from distance to near vision (Ang, 2015). However, accommodative IOLs have come under critical review, as distance-corrected near acuity has not been statistically correlated with axial shift in these lenses. Capsular fibrosis can also impact the presbyopia-correcting capability and induce asymmetric vaulting, leading to lens tilt. This makes the currently available accommodating IOLs challenging to handle at times (Ang, 2016).
- Multifocal IOLs The multifocal category encompasses IOLs that use either refractive or diffractive technology to create simultaneous images on the retina. These lenses split light between distance, intermediate, and near. This technique is used to broaden the range of vision and has been used successfully in well-selected patients. However, users can focus on only one distance at a time, leaving the blur from the other focal points to sometimes cause halos and glare as well as a loss of contrast sensitivity (Ang, 2016).
- Extended Depth of Focus The EDOF class of IOLs is an emerging technology in presbyopia correction that employs methods to improve the range of vision without splitting light rays. The goal of the EDOF IOL is to address patient expectations and demand for presbyopia correction without compromising functional vision across all distances. Rather than creating two or three foci, as with multifocal IOLs, or a single focal point that shifts, as with an accommodating IOL, an EDOF IOL smooths out the dips in the defocus curve to create one elongated focal point (Ang, 2016).
An Exciting Future
Even though a variety of surgical and non-surgical options for presbyopia exist, a perfect one-size-fits-all approach does not yet exist. Each option has demonstrated advantages and disadvantages. However, providing presbyopic patients with safe, functional, and long-lasting vision may soon become a reality. The process of creating successful outcomes will rely on careful patient selection, accurately performed surgery, and a comprehensive approach toward managing patient expectations. CLS
For references, please visit www.clspectrum.com/references and click on document #255.