Eyeworld

EW CORNEA 72 September 2016 by Michelle Dalton EyeWorld Contributing Writer "I admit though that their initial visual results are sometimes remarkable and may be better when compared to what we have been doing as an alternative for more than 10 years now, which is a combined partial topography-guid- ed PRK and high fluence CXL (the Athens protocol). Predictable and long-term visual rehabilitation and stability has proven in our hands to be far better in the Athens protocol patients," he said. Dr. Asbell noted that few sur- gical procedures have a lower risk profile. With Intacs, no tissue is removed, the surgery is done outside the optical zone, and the rings can be removed. PRK and CXL have a higher potential for poor healing leading to scarring and permanent loss of vision, although these com- plications are rare. Using femto Dr. Hardten prefers using a femto- second laser to create the channel, as "the accuracy and depth are more consistent. In cones that are off-cen- ter, I use a 0.45 mm segment in the steeper area, and a 0.21 mm segment in the opposite meridian. I center the larger Intacs at the apex of the cone based on posterior elevation on the Pentacam [Oculus, Wetzlar, Germany]. I do conductive kerato- plasty outside of the segment before creating the channel." Dr. Asbell remains unconvinced about the superiority of femto techniques, finding outcomes to be "pretty similar" between the femto and manual techniques, but said using the femtosecond laser is substantially easier than creating the channel manually. Patient cost may be higher with pass-along facility fees, but there's less discomfort, too, she said. She also advocates using the ring manufacturer's supplied no- mogram, which will evaluate how steep the cornea is, the amount of astigmatism, and whether the cone location is more central or peripher- al, and prefers to make her incisions on the steepest meridian of the cornea. Dr. Kanellopoulos has used a femto laser for more than a decade as an alternative to ICRS implanta- tion, and has found its use to pro- vide much more accurate position- ing than manual channel creation. (based on the Athens protocol introduced more than 10 years ago), especially when cones are decen- tered" in terms of changing both the anterior and posterior curvature of the cornea. It's his clinical experi- ence that the material (PMMA or rigid synthetic materials) "does not seem to be optimally compatible with the corneal collagen long term. More biomechanically and physio- logically compatible materials such as crosslinked human allograph cornea ICRS-like inlays either within the cornea mid-periphery or even within a stromal pocket may have a similar clinical effect with much less long-term morbidity." Experience and the literature There is very little published on long-term data for ICRS. An issue of caution for clinicians is that if and when complications occur, the patient is usually a poor judge of how severe the complication may be—patients usually see well and have minor irritation on their corne- al surfaces even when the segments are migrating and extruding, Dr. Kanellopoulos said. "Sometimes even if a patient gets better vision, he may be unhap- py because of increased glare," Dr. Asbell said. "For these relatively rare patients, we are caught between a rock and a hard place—as clinicians, we want to correct the vision, but we don't want to induce so much glare the patient is even more un- happy." There are many publications on Intacs safety and efficacy, but there are still unanswered questions, such as the stability of the cornea over years post-ring replacement, Dr. Asbell noted. Dr. Kanellopoulos, said the lack of large, longitudinal studies on the long-term safety and efficacy of the rings creates a disser- vice for the current techniques and technologies. "There is no good comparison data in the literature, and there is no long-term data in the literature. It appears that Kerarings may be the leader of the pack at this point as far as their efficacy," Dr. Kanellopoulos said. Because results are "quite unpre- dictable, and long-term stability and safety is questionable," Dr. Kanellopoulos has abandoned using these devices altogether. "Small optical zones will pro- vide greater correction," Dr. Asbell said, "but at the cost of increased and sometimes incapacitating glare." Intacs "can provide improved best spectacle-corrected visual acuity, and perhaps an easier contact lens fitting," in keratoconus patients, Dr. Asbell said. A potential benefit with ICRS is that they can be removed if issues develop, and then the cornea reverts back to baseline. When Dr. Kanellopoulos began using the rings in the late 1990s, "we were very pleased with the results using the rings horizontally and using a thicker ring inferiorly and a thinner or no ring superior to the cone, slightly decentered to 'engulf' the cone center. The visual results were immediate and remark- able, there was significant flattening of the cone and normalization of the posterior concaved surface of the cone, and very useful visual rehabil- itation." But there were complications including melts, extrusions, and even severe infections (one of which happened 15 years post-Intacs surgery). Most patients complained of "significant glare from the rings themselves and from the white material accumulating at the banks of the rings," Dr. Kanellopoulos said, but added many surgeons in Latin America, Asia, and the Middle East have reported significant success with the use of ICRS. Conceptually and biome- chanically in the short term, Dr. Kanellopoulos said rings are "very effective" and "may be superior to using excimer laser normalization with topography-guided techniques I ntracorneal ring segments (ICRS) have been available for more than 20 years as a means to correct myopia, and their use in the treatment of keratoconus spans almost as long. In the U.S., only Intacs corneal implants (Addi- tion Technology, Lombard, Illinois; Oasis Medical, San Dimas, Califor- nia) are approved; outside the U.S., in addition to Intacs, the Ferrara and Keraring (Mediphacos, Belo Horizon- te, Brazil), Bisantis intrastromal seg- mented perioptic implants (Optikon, Rome), and MyoRing (Dioptex, Linz, Austria) are available. Intacs are hexagonal in geom- etry, the Kerarings are triangular, the Ferrara rings are used in a much smaller diameter and thus have a much higher efficacy, said A. John Kanellopoulos, MD, medical di- rector, Laservision.gr Eye Institute, Athens, and clinical professor of ophthalmology, New York Universi- ty Medical School. Another differen- tiating factor is size—the Kerarings have a smaller optical zone, whereas the Intacs are around 7 mm and the Intacs SK around 6 mm. Surgeons in the U.S. are begin- ning to use rings in conjunction with corneal collagen crosslinking for "patients who can't get reason- able vision with a contact lens, yet aren't bad enough to warrant a full corneal transplant," said David Hardten, MD, Minnesota Eye Con- sultants, Minnetonka, Minnesota. There are two main goals in ker- atoconus, said Penny Asbell, MD, professor of ophthalmology, Icahn School of Medicine at Mount Sinai, New York: provide better vision, and stabilize the corneal shape. Intracorneal ring segment use remains controversial Patient with intracorneal ring segments Source: A. John Kanellopoulos, MD Device focus

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