EyeWorld Asia-Pacific December 2017 Issue

Refractive opportunities – from page 45 December 2017 46 EWAP SECONDARY FEATURE Views from Asia-Paci c Adj. Assoc. Prof. LIM Li, MBBS, MMed(Ophth), FRCS(Ed), FAMS(S’pore) Senior Consultant, Corneal and External Eye Disease Service Singapore National Eye Centre 11 Third Hospital Avenue, Singapre 168751 Adj. Assoc Professor, Duke NUS Graduate Medical School Singapore Tel. no. +65-62277255 Fax no. +65-62263395 lim.li@snec.com.sg Customized Corneal Collagen Crosslinking for Keratoconus R oberts and Dupps proposed that the biomechanical weakness in keratoconus is focal in nature, rather than a uniform generalized weakening. 1 In a study using computational modeling techniques, Roy and Dupps demonstrated differential biomechanical weakening in the area of the cone and proposed that greater efficacy of crosslinking treatment may be achieved with smaller diameter cone-centric patterns. 2 The Mosaic delivery system (KXL II, Avedro Inc., Waltham, Massachusetts, CE mark) offers customized crosslinking that allows for UV-A irradiation in customized treatment patterns localized on specific corneal zones. Seiler et al. 3 reported on the comparison of customized crosslinking and conventional crosslinking (20 eyes in each group) for keratoconus and found that 37% in the customized group achieved 2 D or more of flattening compared to 11% in the standard group. Mazotta et al. 4 showed that besides reduction in topographic astigmatism, there was also no corneal endothelial cell loss. Hence, current preliminary results on customized crosslinking for keratoconus show a greater flattening effect on the cornea compared to conventional crosslinking with superior visual results. Further studies are required to further customize the treatment approach to optimize outcome. LASIK Xtra The LASIK procedure weakens the cornea and in rare cases may cause LASIK keratectasia, a serious and visually debilitating complication. In an effort to strengthen the post LASIK cornea, LASIK Xtra was introduced and involves simultaneous high irradiance crosslinking in addition to the LASIK procedure. The LASIK procedure is performed and after excimer laser ablation, a higher concentration 0.25% riboflavin is applied on the stromal bed with a soak time varying from 45 to 90 seconds. The flap is then repositioned after the riboflavin is rinsed away from the interface. The UV-A irradiation is performed at 30 mW/cm 2 for a duration varying from 45 to 90 seconds, delivering a total fluence varying from 1.4 to 2.7 J/cm 2 (figure 1). Studies on the outcomes of LASIK Xtra show greater stability of refraction. 5 Contralateral study comparing the results of LASIK with or without concomitant crosslinking in hyperopic eyes demonstrated a significantly lower regression in the LASIK Xtra group. 6 For high myopia treatments, Kanellopoulos et al. showed a lower refractive shift and greater keratometric stability in the Xtra group at the 2-year follow-up. 7 Hence, studies on LASIK Xtra show significant improvement in refractive stability with reduced regression. Further long-term studies are required to determine whether this procedure is able to reduce postoperative LASIK keratectasia in high-risk individuals. Photorefractive intrastromal crosslinking (PiXL): High-fluence corneal collagen crosslinking for low myopia High-fluence corneal collagen crosslinking for low myopia is a novel treatment involving high-fluence irradiation (ranging from 10–15 J/cm 2 ) using the Mosaic device (Avedro) to induce subsequent flattening and refractive correction. A preliminary study by Kanellopoulos showed that PiXL for low myopia achieved a mean myopic correction of 1.4 D with no significant endothelial cell loss. 8 Further studies on PiXL may include the addition of supplemental oxygen to enhance the efficacy of epithelium-on approach, and topographically guided treatments. References 1. Roberts CJ, Dupps WJ Jr. Biomechanics of corneal ectasia and biomechanical treatments. J Cataract Refract Surg. 2014;40:991–8. 2. Roy AS, Dupps WJ Jr. Patient-specific computational modeling of keratoconus progression and differential responses to collagen cross-linking. Invest Ophthalmol Vis Sci . 2011;52:9174–87. 3. Seiler TG, Fischinger I, Koller T, et al. Customized corneal cross-linking: One-year results. Am J Ophthalmol. 2016;166:14–21. 4. Mazzotta C, Moramarco A, Traversi C, et al. Accelerated corneal collagen cross- linking using topography-guided UV-A energy emission: Preliminary clinical and morphological outcomes. J Ophthalmol. 2016;2016:2031031 5. Rajpal RK, Wisecarver CB, Williams D, et al. Lasik xtra provides corneal stability and improved outcomes. Ophthalmol Ther. 2015;4:89–102. 6. Kanellopoulos AJ, Kahn J. Topography-guided hyperopic LASIK with and without high irradiance collagen cross-linking: Initial comparative clinical findings in a contralateral eye study of 34 consecutive patients. J Refract Surg. 2012;28:S837–40. 7. Kanellopoulos AJ, Asimellis G. Combined laser in situ keratomileusis and prophylactic high-fluence corneal collagen crosslinking for high myopia: Two-year safety and efficacy. J Cataract Refract Surg. 2015;41:1426–33. 8. Kanellopoulos AJ. Novel myopic refractive correction with transepithelial very high- fluence collagen cross-linking applied in a customized pattern: Early clinical results of a feasibility study. Clin Ophthalmol . 2014;8:697–702. Editors’ note: Dr. Lim declared no relevant financial interests. Figure 1. LASIK Xtra procedure Source: Lim Li, MBBS, MMed(Ophth), FRCS(Ed), FAMS(S’pore)