EyeWorld Asia-Pacific September 2013 Issue

52 EWAP rEfrActivE September 2013 Views from Asia-Pacific CHAN Wing Kwong, MD Visiting Consultant, Singapore National Eye Centre 11 Third Hospital Avenue, Singapore 168751 Eye & Retina Surgeons #13-03 Camden Medical Centre, 1 Orchard Boulevard, Singapore 248649 Tel. no. +65-6738-2000 Fax no. +65-6738-2111 wkchan@me.com T hese 3 products described are a new class of corneal inlay devices that are used to correct presbyopia. The KAMRA uses the pinhole effect to improve the depth offocus, 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. All are implanted in the corneal stroma after a LASIK type flap or a corneal pocket is created with a femtosecond laser. They are all implanted in one (the nondominant) eye. They all cause a slight drop in distance vision of between 1 to 2 Snellen lines in return for a gain of near vision and 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, the manufacturers say. Have we found the fountain of youth? Have we solved the most difficult refractive problem in ophthalmology? Sounds too good to be true? Perhaps some circumspection is deserved. There are a few issues that we have to consider: 1. Centration of the device To work effectively, all the devices have to be centered on the pupil. Any decentration of the device will lead to a drop in efficacy and rise in visual side effects with progres- sive deviation from the ideal location. However, there is no agreement on exactly where in the center of the pupil these devices should be centered on. Should it be the center of the entrance pupil or centered with respect to the first Purkinje reflex? Even if we knew where best to center the device, how do we mark and refer to this position intraoperatively? There will need to be development and deployment of intraoperative microscope mounted real-time centering instruments in tandem with the launch of these devices. 2. Biocompatibility All three devices claim to be biocompatible having gone through rigorous animal and human studies. However, there have been anecdotal reports of corneal haze develop- ment related to these devices in some patients. If the cornea reacts with haze, then how could these device materials be truly biologically inert? Is the haze related to a corneal fibroblastic response of new collagen deposition, much like a corneal scar formation, or is it due to deposition of new extracellular matrix from corneal fibrocytes. Clinicians can see this corneal response in some eyes but the manufacturers do not seem to be addressing this issue actively. We need to be aware that what is inert on the corneal surface (like a contact lens-like material) or inside the eye (like an IOL-like 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 devices causing a refractive shift to hyperopia or myopia with some of these devices in a minority of patients. While a shift to myopia may be useful to the presbyope, a hyperopic shift will negate any reading ability that the eye had before. Why do these shifts 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 devices keep up their efficacy with increasing degrees 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 devices lose their efficacy? Long-term studies of 5 -10 years will answer this question as we should know the useful presbyopic correcting lifespan of these devices 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 devices could offer and if a 55 year old could be better off considering multifocal IOLs rather than these devices as they may not function best with their low level of residual accommodation. These corneal inlay devices present a ray of hope in our quest to correct presbyopia—the “Holy Grail” of refractive surgery. To gain universal applicability and safety for our prospective patients, the four issues that I have raised should be answered to our complete satisfaction. Editors’ note: Dr. Chan has no financial interests related to his comments. Corneal - from page 51