EyeWorld Asia-Pacific June 2016 Issue

June 2016 50 EWAP CORNEA Views from Asia-Paci c CHAN Wing Kwong, MD Eye & Retina Surgeons #13-03 Camden Medical Centre, 1 Orchard Boulevard, Singapre 248649 Tel. no. +65-6738-2000 Fax no. +65-6738-2111 www.eyeretinasurgeons.com P resbyopia is THE most dif cult and enigmatic refractive error to treat. Patients are frustrated by their need to use inconvenient and un attering reading glasses at a stage that they consider to be the prime of their lives. Ophthalmologists are hampered by the lack of effective, predictable, and stable methods or devices to treat presbyopia with unquali ed success, unlike cataract surgery or refractive surgery for myopia and astigmatism. Why is the treatment of presbyopia so elusive? It is because we are not treating the physiological cause for presbyopia, which is the loss of accommodative power of the eye with increasing age. Everything we have been doing to treat presbyopia has been through what I call “proxy optical methods”, with reading glasses, to contact lenses, to monovision, and even multifocal IOLs. All these methods don’t treat the progressive loss of accommodation with increasing age. The products described in these two articles are a new class of devices designed to be implanted in the corneal stroma. The KAMRA uses the pinhole effect to improve the depth of focus, the Raindrop steepens the central cornea without any refractive power while the Flexivue microlens has a plus power to make the central cornea have a slightly higher refractive power to improve near vision. They do not directly address the loss of accommodation. Like other methods before, they use optical principles to treat presbyopia by proxy. All are implanted in the corneal stroma after a LASIK-like ap or a corneal pocket is created with a femtosecond laser. They are all implanted in one eye (the non-dominant eye). They all cause a slight drop in distance vision of between 1 to 2 lines in return for a useful gain of near vision and, most importantly, the prospect of freedom from reading glasses. They all promise reversibility and applicability to millions of presbyopes, whether emmetropic or ametropic, whether phakic or pseudophakic. It is not monovision and any surgeon who can do LASIK can do this surgery. Have corneal inlays brought us one step closer to solving the most dif cult refractive problem in ophthalmology? Sounds too good to be true? I think some circumspection is well deserved. It is wise to note Dr. Tamayo’s comments. He sums it up best by stating that these inlays are not for every presbyope, it is not a replacement for the loss of accommodation, and potential patients have to accept a little loss of distance vision in the implanted eye. In other words, patients have to accept compromises. There are some questions that deserve consideration. I should state that my experience has only been with the KAMRA inlay and, therefore, the following issues are only quali ed with respect to the inlay manufactured by AcuFocus. 1. Centration of the inlay To work effectively, all the inlays have to be centered on the pupil. Any decentration of the inlay will lead to a drop in ef cacy and rise in visual side effects with progressive deviation from the ideal location. However, there is no agreement on exactly where in the center of the pupil these inlays should be centered on. Should it be the center of the entrance pupil or centered with respect to the 1st Purkinje re ex? Even if we knew where best to center the inlay, how do we mark and refer to this position intraoperatively? The AcuTarget HD introduced for KAMRA is a step in the right direction to achieve optimal inlay centration. 2. Biocompatibility All the inlays claim to be biocompatible having gone through rigorous animal and human studies. However, there have been anecdotal reports of corneal haze development related to these inlays in some patients. If the cornea reacts with haze, then how could these inlay materials be truly biologically inert? Is the haze related to a corneal broblastic response of new collagen deposition, much like a corneal scar formation, or is it due to deposition of new extracellular matrix from corneal brocytes? Clinicians can see this corneal response in some eyes but the manufacturers do not seem to be addressing this issue adequately. We need to be aware that what is inert on the corneal surface (like a contact lens polymer) or within the eye (like an IOL material) may not exhibit these same privileges when it is implanted in the corneal stroma. 3. Refractive shifts There are anecdotal reports of some of these inlays causing a refractive shift to hyperopia or myopia in some patients. While a shift to myopia may be useful to the presbyope, a hyperopic shift will negate any reading ability that eye had before. Why do these shifts occur? Corneal topography shows a relative central corneal attening compared to the preoperative map. But why does this attening occur? We do not know yet. Could it be related to the corneal haze that is observed in some of these eyes? We do not know yet. There is much work to be done to explain these observations. 4. Presbyopia is progressive Do these inlays keep up their ef cacy with the increasing degree of presbyopia as we age? Or do they work only for the younger presbyopes and as we grow older and the level of accommodation decreases, these inlays lose their ef cacy? Long-term follow-up of implanted patients will answer this question. We should know the useful presbyopic correcting lifespan of these inlays when we implant them. It is important information to be able to tell the 45-year-old presbyope how many useful spectacle free years these inlays could offer and should a 55-year-old be better off considering multifocal IOLs rather than these inlays as they may not function the best with their lower levels of residual accommodation. These corneal inlays offer a ray of hope in our quest to correct presbyopia. To gain universal applicability and safety for our presbyopic patients, the issues that I have raised should be answered to our complete satisfaction. The correction of presbyopia will continue to be a story of compromises, of gains and losses, unless and until scientists and ophthalmologists are able to restore accommodation to the aging eye. Only then will we be able to say we can cure presbyopia. Editors’ note: Dr. Chan declared no relevant nancial interests. Presbyopia inlays - from page 49