EyeWorld Asia-Pacific December 2017 Issue

customized group (compared to 11% in the standard group) had 2 D or more of flattening at 1 year postop, as well as a better epithe- lial healing time, change in Kmax, and regularization. 2 Another paper published earlier this year showed similar safety of standard crosslinking compared to topog- raphy-guided but with a stronger flattening effect and better im- provement in corrected distance visual acuity in the latter group. 3 When it comes to customized crosslinking, Dr. Dupps pointed to a couple of subtleties that he said could be important for this type of treatment. There are two differ- ent ways to calculate curvature of the cornea—axial curvature and tangential curvature—which he said with keratoconus could give two very different locations for the steepest part of the cone. “We at least need to carefully report exactly what curvature metric is being used to guide [cus- tomized treatment] and then as- sess the outcomes in light of that,” Dr. Dupps said. Dr. Dupps said there isn’t a tool yet that identifies the weakest point of the cornea—steepest cur- vature point acts as a surrogate for now—but he said emerging tools like Brillouin microscopy and OCT elastography are in trans- lational trials and could provide this information in the future. Dr. Elling pointed to a 2014 study that used Brillouin microscopy to show that stromal weakening in keratoconus is concentrated in the region of the cone. 4 The other factor brought up by Dr. Dupps is how long the customized treatment effect lasts. “Keratoconus is a progressive condition. If you initially have a small zone of weakening, but then 20 years later you have progressive weakening of untreated peripheral corneal regions, the shape may continue to change. This might explain some cases of progres- sive central corneal flattening after CXL, so there is a question of whether or not we should still be delivering some crosslinking treatment to the whole cornea while concentrating more treat- ment in the weakest area. That’s another important open question that needs further investigation,” he said. “In terms of cons, a disadvan- tage [of customized crosslinking] that I can think of is that more physician input is required into determining the appropriate treat- ment pattern for each patient,” Dr. Elling said. “However, this may become easier over time as the ophthalmic community gains experience with the procedure. “We have treated a few cases of irregular corneal astigmatism using this approach and have been very satisfied with the outcomes, particularly in terms of visual im- provement,” Dr. Elling said. LASIK Xtra It’s well established that LASIK can weaken the cornea and in some rare cases result in refrac- tive drift or corneal ectasia. Crosslinking has been established to strengthen the corneal collagen bonds, so why not combine the two procedures? That’s the con- cept behind LASIK Xtra (Avedro, Waltham, Massachusetts). “Published data on corneal crosslinking demonstrates that the procedure adds strength to the cornea, therefore the concept be- hind the combination procedure is an interesting one,” Dr. Elling said, adding that he does not have personal experience with it, but noted that “the published litera- ture supports the concept that CXL can add safety to the LASIK procedure, and that there is likely an improvement in refractive sta- bility in highly myopic or hyper- opic patients.” He also mentioned other work that suggests better continued on page 48 December 2017 EWAP SECONDARY FEATURE 47