The final frontier

Effective treatment of presbyopia remains the last frontier of refractive surgery, but important progress has been made in recent years, Günther Grabner MD told delegates attending the Refractive Surgery Course at the 21st ESCRS Winter Meeting in Maastricht, The Netherlands. “There are currently two anatomical locations amenable to treatment for presbyopia: the cornea and the natural lens,” said Dr Grabner, Chairman Emeritus, University Eye Clinic Salzburg, Paracelsus Medical University, Salzburg, Austria. A third location, the anterior chamber, has long been abandoned. New treatment modalities are emerging, although some appear to be of questionable quality, he noted. “Beware of any potential procedures that aim to treat presbyopia based on disproven theories of accommodation, such as the effect of increasing equatorial zonular tension or the proposed piston-like movement of the crystalline lens,” he warned. It is only Helmholtz’s theory of accommodation, in which optical change in the dioptric power of the lens is the driving force, that has been experimentally and clinically proven in almost all aspects, he asserted. Further, there are several types of true accommodation. The first is 'blur-driven', which is stimulated by defocus. The second, 'vergence-driven', is controlled by the accommodation-convergence reflex. The third is due to pharmacologic stimulation by a muscarinic cholinergic agonist such as pilocarpine. Before delving into surgical solutions to presbyopia, however, Dr Grabner reminded delegates that the conservative treatment modalities for presbyopia, namely reading glasses and contact lenses, remain excellent choices. “They are easily adjustable, very stable, fully reversible and offer high contrast, making them especially ideal for very critical patients.” Currently, the most frequently performed surgical presbyopia treatment is the creation of monovision in which the non-dominant eye is targeted to mild myopia. This can be performed with various surgical procedures, including lens exchange, LASIK, LASEK and photorefractive keratectomy (PRK). A pre-surgical test with contact 
lenses is mandatory. People in professions that require good stereopsis at near distance, such as plumbers, are not good candidates for monovision, he reminded delegates. Corneal surgical options abound, with the advantage that they are extraocular and at least partially reversible, as opposed to lens surgery. Possibilities include laser and intracorneal inlays or implants. “PresbyLASIK is a proven technology that has been around for a long time, of which the most promising is the so-called global optimum technique,” said Dr Grabner. Central presbyLASIK is particularly good for near vision while distance vision suffers slightly, whereas peripheral presbyLASIK performs the opposite, 
he reported. Dr Grabner is particularly enthusiastic about non-linear aspheric micro-monovision, which maintains functional stereo acuity. Intracor, an intrastromal femtosecond laser correction, is an irreversible procedure, that seems less promising, with up to 20% of patients left unsatisfied, he said. CORNEAL INLAYS What about corneal inlays? This tissue-sparing, removable modality includes microlens systems such as the Raindrop, Icolens and Flexivue, as well as the “small aperture” Kamra. “The corneal inlays, which are microlenses that are placed in the non-dominant eye’s cornea, offer a wide range of defocus and good bilateral uncorrected distance visual acuity [UDVA] with no decrease in binocular contrast sensitivity. However, a drop of DVA in the operative eye has to be stated,” said Dr Grabner. The Kamra inlay is not a lens but rather a central aperture that improves near vision by extending depth of focus. A study with one year follow-up in nearly 1800 patients reported 95% satisfaction rate, and it has been FDA-approved since 2015. However, complications such as epithelial ingrowth, decentred inlays and hyperopic shift are potential, albeit rare, problems. Moving more posteriorly, anterior chamber phakic multifocal IOLs have largely been abandoned due to complications, and surgical procedures that target the sclera have never taken off as viable options. More promising are lenticular solutions. Lens corrections offer the promise of established surgery with well-known materials and optical principles, large series and known side effects such as some glare, halos, loss of contrast sensitivity and insufficient intermediate vision, said Dr Grabner. The optical quality of multifocal IOLs has gotten much better than even several years ago, but Dr Grabner finds that they need to improve further. “The search for solutions with fewer side effects, better depth of focus and more natural ‘accommodating’ properties has led to the development of alternatives,” he said. “The IC-8 is a small-aperture, single-piece hydrophobic acrylic IOL from AcuFocus that generates added depth of focus in the same manner as the Kamra corneal inlay,” explained Dr Grabner. Accommodating IOLs have been introduced and more than a half 
dozen models have been produced. The contrast sensitivity is equal to that of a monofocal IOL, but they are rather complex. As no peer-reviewed publications have been published to date, accommodating IOLs have a long way to go before they are widely accepted, 
he told the session. Topical drops that increase lens elasticity via reduction of lens protein disulfides have also been tested, but are unlikely to be clinically available for quite some time. Until then, multifocal IOLs will remain the primary option for most surgeons. “No technique is perfect. There is always a compromise,” Dr Grabner concluded. Günther Grabner: 
g.grabner@grabner-augen.at