Eyeworld

APRIL 2019 | EYEWORLD | 115 C A 2017 retrospective study in the Journal of Cataract & Refractive Surgery focused on the demarcation line depth after CACXL in 21 eyes. 3 Researchers found that hydroxypropyl methylcel- lulose-based riboflavin led to a deeper demarca- tion line than dextran-based riboflavin. However, both solutions were safe for the endothelium at 6 months. A study published in Acta Ophthalmologica analyzed the biomechanical effect of CACXL in post-mortem porcine eyes and found there was about a third less of a biomechanical effect after CACXL compared with the standard approach. 4 Efficacy for CACXL might be bolstered by lower- ing or omitting the riboflavin film on the contact lens, the authors concluded. A study in 2015 in the Journal of Refractive Surgery, however, showed that CACXL showed greater effect in murine corneas, which are more similar to the thin corneas that CACXL treats, than in porcine corneas, which are similar to corneas with higher thickness. 5 This study showed that the amount of absorbed UV light was more important in porcine than in murine corneas and that the higher oxygen availability in thin corneas potentially increases overall efficacy of crosslink- ing in thin corneas as compared to corneas of standard thickness. Dr. Jacob continues to expand her study of keratoconus treatments with the corneal allogenic intrastromal ring segments technique (CAIRS). The technique uses the corneal allogenic intras- tromal ring segment in patients with keratoconus, followed by either accelerated conventional or accelerated contact lens-assisted CXL. A pilot study with 24 patients found that the technique, combined with CXL, was safe and effective for keratoconus, giving significant improvements in almost all parameters including uncorrected and spectacle corrected distance visual acuity. 6 Dr. Jacob has now performed CAIRS in about 80 patients. (320–350 microns), if CACXL does not lead to the 400-micron benchmark as measured by intraop pachymetry, Dr. Jacob uses two drops of distilled water to help the functional pachyme- try quickly reach 400 microns. This is quick and simple to attain since a large volume of corneal swelling is not required as the bulk of functional increase in pachymetry is already provided by the riboflavin-soaked contact lens. Dr. Jacob said to make sure that the contact lens being used does not have a UV filter, which many contact lenses have. "If the lens has a UV filter, in effect you are doing nothing at all," she said. She frequently uses the SofLens Daily Disposable (Bausch + Lomb), which is made with hilafilcon B and is widely available. After treatment, patients are patched for the night and receive a new bandage contact lens the next day until epithelial healing. Postop care for CACXL patients is similar to that for conventional CXL patients. Dr. Jacob advises patients to avoid any mechanical stress on the eye. She also monitors for keratoconus progression using refraction, keratometry, pa- chymetry, and Kmax measurements. As for all crosslinking procedures, she keeps a close watch on patients to check for signs of progression. "We've been very pleased with our results with CACXL and fortunately have an extremely low rate for retreatment," she said. What the studies show More surgeons around the globe are now us- ing CACXL as well. It is performed at about 80 branches of the hospital where she works in India. Additionally, several published studies from Dr. Jacob and other researchers provide more evidence about the effectiveness of CACXL and help refine the technique. A 2016 study included 10 eyes and found that CACXL increased functional corneal thickness and that in vivo confocal microscopy changes were similar to those seen with conventional CXL. This study recommended the use of AS- OCT after contact lens application but before UV treatment to confirm there is a functional thick- ness of 400 microns or more. 2 References 1. Jacob S, et al. Contact lens-as- sisted collagen cross-linking (CACXL): A new technique for cross-linking thin corneas. J Refract Surg. 2014;30:366–72. 2. Mazzotta C, et al. In vivo confocal microscopy after contact lens-assisted corneal collagen cross-linking for thin kerato- conic corneas. J Refract Surg. 2016;32:326–31. 3. Malhotra C, et al. Demar- cation line depth after contact lens-assisted corneal crosslinking for progressive keratoconus: Comparison of dextran-based and hydroxypropyl methylcellu- lose-based riboflavin solu- tions. J Cataract Refract Surg. 2017;43:1263–1270. 4. Wollensak G, et al. Biomechani- cal efficacy of contact lens-as- sisted collagen cross-linking in porcine eyes. Acta Ophthalmol. 2019;97:e84–e90. 5. Kling S, et al. Increased biomechanical efficacy of corneal cross-linking in thin corneas due to higher oxygen availability. J Refract Surg. 2015;31:840–6. 6. Jacob S, et al. Corneal allo- genic intrastromal ring segments (CAIRS) combined with corneal cross-linking for keratoconus. J Refract Surg. 2018;34:296–303. Financial interests Jacob: None

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