We read with interest the article by Vilupuru and associates comparing contrast sensitivity in eyes with corneal inlays, accommodating intraocular lenses, and bifocal intraocular lenses. The study reported the results of small-aperture corneal inlay implantation (Kamra, model ACI7000PDT) in 327 emmetropic and presbyopic eyes with a preoperative spherical equivalent between −0.75 and +0.50 diopter (D), and no more than 0.75 D of astigmatism, who were followed for 6 months. In Table 1 the authors showed that the final sphere range was between −2.50 and +3.25 D. It would be very useful to know how many eyes were beyond the range of ±0.75 D of spherical equivalent, which would be related to postoperative refractive shifts compared to their initial refractive status.
Several authors report refractive shifts following Kamra corneal inlay implantation. Dexl and associates found 5 cases of hyperopic shift at 5 year follow-up of 32 eyes implanted with the ACI7000 model (10 μm thick) inlay under a 170 μm corneal flap. Explantation of the inlay was performed in 1 eye with +2.25 D of spherical equivalent. The authors suggested that stromal thickening over the inlay annulus could induce the corresponding corneal surface to move forward, causing central flattening over the inlay aperture, resulting in the hyperopic refractive shift. In a recently published series by Tomita and Waring, at least some eyes had refractive shifts following implantation, since 1 year postoperatively the spherical equivalent range was very large: from −2.88 to +2.25 D in one group of cases, and from −3.25 to +4.25 D in another group (divided according to age). Similarly, at 4–6 months post-surgery 2 of our patients who had the model ACI7000PDT implanted under a femtosecond laser pocket at a depth of 200 μm showed a hyperopic shift of between +2.75 and +2.88 D spherical equivalent. We are preparing a detailed case series report on those eyes.
Using confocal microscopy, high levels of keratocyte activation have been detected in some corneas following corneal inlay implantation. The keratocyte activation has been associated with a mild haze around the margin of the inlay and a topographic appearance of a ring of hotter colors (reds and oranges) corresponding to the location of the implant, and colder color in the central area, corresponding to the aperture of the inlay.
Since Kamra inlay is a new alternative for presbyopia correction and candidate patients usually have high expectations, if the procedure leads to a refractive shift that diminishes their previously adequate uncorrected distance visual acuity, they will be highly dissatisfied. Therefore, although this is not a common outcome, we believe that research is warranted to establish its true incidence and identify measures for prevention and treatment.