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MMC may help reduce haze associated with Raindrop inlay implantation
A small study shows the use of MMC does not change endothelial cell counts and no visual acuity is lost.
The concept of corneal inlays dates back a few decades, and the commercial introduction of the Kamra from AcuFocus and the Raindrop near vision inlay from ReVision Optics has cemented their use in our practices as an additive way of correcting presbyopia without ablating corneal tissue. Inlays are implanted in the stromal tissue and can be removed if needed. All procedures have been shown to improve near function without compromising distance vision because inlays are unilaterally implanted in the nondominant eye.
Commercial outcomes have been positive, but there are some drawbacks, namely corneal haze, diminished nutrient supply and pupil size dependency. I have been using the Raindrop near vision inlay since 2013; this particular inlay is 2 mm in diameter and 32 µm thick, or about half the thickness of a human hair. One of its primary advantages over other inlay technologies is that it is composed of transparent hydrogel that has a similar refractive index and water content as the cornea; the positive meniscus shape creates a smooth and continuous power transition. My technique is to implant the device at the center of a light-constricted pupil under a femtosecond laser-created flap. This shape-changing procedure biomechanically alters the corneal shape by raising the anterior stroma. There is virtually no effect past twice the diameter of the inlay, with the greatest effect residing on the center of the inlay.
In our initial series of 28 eyes implanted with the Raindrop, in 28 patients with a mean age of 54 ± 4.61 years, our patients achieved excellent near visual acuity with 74% achieving N5, and more importantly, their range of vision was unaltered from 30 cm through 50 cm. Monocular distance visual acuity decreased one line, from 0.09 logMAR to 0.21 logMAR. But we also noticed haze in a few subjects, up to 29% (Figures 1 and 2).
Figure 1. Monocular range of vision, baseline to 3 months postoperatively.
Figure 2. Incidence and severity of central corneal haze without MMC.
Mitomycin C, corneal haze and corneal inlays
Mitomycin C is often used in our clinic in refractive procedures such as epi-LASIK or PRK to prevent haze in the postoperative period. When we started to notice that patients who received inlays also reported haze, mostly grade 1 or less, and that the incidence increased the further out from surgery they were, we thought MMC may help prevent its development. In corneal inlays, we believe the excessive wound healing results in peripheral inlay stromal fibrosis, and that, in turn, can cause irregular astigmatism, reduced vision, photic phenomenon and “ghost” images. In a review of published literature, Arlt and colleagues noted complaints such as halo are rare with the Raindrop, and only one patient had the inlay removed due to unresolved haze. Another group reported a 13% incidence of transitory haze in his slightly hyperopic patient group that resolved after two rounds of steroids. A slightly higher rate of 16.6% is reported by ReVision Optics.
We hypothesized the same prophylactic advantages of using off-label MMC in refractive corneal procedures such as epi-LASIK and PRK would apply in corneal inlays and decided to conduct a clinical study combining both Raindrop and MMC under the flap.
Surgical technique
For all patients in our cohort, we created a femtosecond laser flap 160 µm deep followed by excimer ablation on the stromal bed in patients who needed a refractive tune-up — aiming for +0.75 D to counteract the mild myopic shift induced by the Raindrop — with MMC 0.02% applied on both the stromal bed and underside of the flap for 15 seconds. I rinsed both surfaces thoroughly with 10 cc of balanced salt solution. At this point I dried the stromal bed meticulously using a microsponge and then proceeded to deliver the Raindrop inlay. The flap is closed after the inlay starts showing an orange-peel appearance, which means it is dry and stuck to the stromal bed.
We evaluated 22 eyes of 22 patients with a mean age of 47.68 ± 5.04 years. The mean add was 1.32 ± 0.53 D, and the mean spherical equivalent was 0.31 D. All patients signed an informed consent, and follow-up was set at day 1, week 1 and months 1, 2, 3, 6, 9 and 12.
Our patients showed similar or better visual acuities with MMC than without it. At 6 months or later, all subjects achieved N5 or better near at their preferred reading distance (Figure 3). The mean monocular distance visual acuity was 6/7.5 (20/25 Snellen), and all eyes could see 6/12 or better (20/40). Refraction remained stable over time.
Figure 3. Uncorrected near visual acuity.
Figure 4. Incidence and severity of central corneal haze with MMC.
Importantly, there were no changes in endothelial cell counts over time. Patient satisfaction was positive; in the group without MMC at 6 months, 81% were satisfied, 13% neutral and 6% dissatisfied. In the patients implanted in association with MMC, 94% were satisfied, 6% neutral and 0% dissatisfied. This trend remained at 12 months (“satisfied or better” response improved to 90% and 100%, respectively), but the sample size is too small to compare.
I plan on continuing to use MMC in all my future inlay patients because I feel that the risk and severity of corneal haze with the Raindrop can be alleviated prophylactically with this agent, and the use of MMC is safe, with no changes in endothelial cell counts and no loss in visual acuity.
Reference:
Arlt EM, et al. Clin Ophthalmol. 2015;doi:10.2147/OPTH.S57056.
Disclosure: Theng reports he is a consultant for ReVision Optics.