EyeWorld India March 2013 Issue

41 EWAP REFRACTIVE March 2013 Views from Asia-Pacific Colin CHAN, MD, MBBS(Hons), FRANZCO Conjoint Associate Professor, SOVS, Faculty of Sci- ence, UNSW Clinical Senior Lecturer, Central Clinical School, University of Sydney Vision Eye Insititue Level 4, 270 Victoria Ave., Chatswood, NSW 2067 Australia Tel. no. +61-9424-9999 Fax no. +61-94215-4220 colin.chan@vgaustralia.com P ost-LASIK ectasia is a devastating complication for both the patient and the refractive surgeon, hence the desperate search for either a screening or treatment method to reduce the incidence of ectasia. Current screening methods do not identify all patients with abnormal corneas. For example, the Randleman Ectasia Risk Factor score 1,2 , while probably one of the better screening scales, in our retrospective review would have only identified 56% of ectasia patients preoperatively as high risk. 3 There are too many unknowns about accelerated crosslinking after LASIK or LASIK Xtra to conclude whether it can reduce the incidence of post-LASIK ectasia. Firstly, there are no peer-reviewed publications to confirm that accelerated crosslinking actually works like conventional crosslinking. Secondly, even if there was evidence that accelerated crosslinking worked in keratoconus, the parameters used when it is applied in LASIK Xtra are different again (45 seconds UV exposure versus 3 minutes). Therefore, no conclusions can be made about its safety and efficacy with this set of parameters. Thirdly, crosslinking as a prevention modality is quite a different proposition from crosslinking as a treatment modality. Ectasia takes a median time of 4 years to occur and is rare; so sufficient longitudinal data and significant numbers are needed to prove LASIK Xtra works. 4 My opinion is that there needs to be prospective data on LASIK Xtra before it can be embraced as preventative treatment for ectasia in high risk corneas. Until then, the best prevention is in careful case selection. Abnormal corneal topography seems to be consistently the best predictor of post-LASIK ectasia and if a cornea is potentially at risk for ectasia, my advice would be simple: don’t operate. References 1. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology . 2008 Jan;115(1): 37-50. Epub 2007 Jul 12. 2. Randleman JB, Trattler WB, Stulting RD.Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening. Am J Ophthalmol. 2008 May;145(5):813-8. doi: 10.1016/j.ajo.2007.12.033. Epub 2008 Mar 10. 3. Chan CC, Hodge C, Sutton GExternal analysis of the Randleman Ectasia Risk Factor Score System: a review of 36 cases of post LASIK ectasia. Clin Experiment Ophthalmol. 2010 May;38(4):335-40. 4. Raj R, Sutton G, Hodge C. “Incidence of Keratectasia after LASIK.” Under review J Refract Surg. Editors’ note: Prof. Chan has no financial interests related to his comments. Lim Li, MBBS, FRCS(Ed), MMed(Ophth), FAMS Head (Clinical Service and Education) and Senior Consultant, Corneal & External Eye Disease Service Singapore National Eye Centre 11 Third Hospital Ave., Singapore 168751 Tel. no. +65-62277255 lim.li@snec.com.sg C orneal collagen crosslinking treatment has been shown to be effective in stabilizing corneal ectatic conditions such as keratoconus and post-LASIK keratectasia. 1-3 The creation of a LASIK flap reduces the biomechanical strength of the cornea. The structural integrity of the cornea can be weakened especially in high myopia treatment. In recent years, post-LASIK iatrogenic keratectasia has become a significant problem for many refractive surgeons and LASIK patients. Over time, with the increasing number of eyes treated with LASIK, more and more corneas are likely to suffer mechanical fatigue resulting in ectasia. The incidence of post-refractive corneal ectasia is unknown, but it has been estimated by some to be as high as 1 in 1000 cases after LASIK surgery. Traditionally, corneal collagen crosslinking is generally performed by removing the corneal epithelium and then pretreating the cornea for 30 minutes with 0.1% Riboflavin Ophthalmic Solution to saturate the corneal tissue with the riboflavin photosensitizer. The cornea is then irradiated with UVA (365 nm) at 3 mW/cm2 for 30 minutes. The whole procedure takes an hour to perform. By using higher UVA irradiance, the Avedro corneal crosslinking system significantly reduces crosslinking time from one hour to a few minutes. There are currently two indications for this system: KXL procedure for the treatment of keratoconus and LASIK ectasia and the Lasik Xtra procedure for prophylactically crosslinking during LASIK surgery. Both procedures have received the CE mark approval for use in Europe and are currently undergoing FDA trials in the USA. However, prophylactic crosslinking in LASIK is a new emerging technique with few published results todate. Celik4 reported in a case series of 8 eyes (fellow eye as control) that the LASIK – CXL group had equal or better visual outcome than the LASIK only group. Further long term follow-up and clinical evaluations are required. References 1. Wollensak G, Spoerl E, Seiler T. Riboflavin/Ultraviolet-A-induced collagen cross- linking for the treatment of keratoconus. Am J Ophthalmol . 2003; 135:620-627. 2. Caporossi A, Mazzotta C, Baiocchi S, Caporossi T. Long term results of riboflavin ultraviolet a corneal collagen cross-linking for keratoconus in Italy: the Siena eye cross study. Am J Ophthalmol . 2010 Apr;149(4):585-93. 3. Vinciguerra P, Albe E, Trazza S, Seiler T, EpsteinD. Intraoperative andpostoperative effects of corneal collagen cross-linking on progressive keratoconus. Arch Ophthalmol . 209 Oct;127(10):1258-65. 4. Celik HU, Alagöz N, Yildirim Y, et al. Accelerated corneal crosslinking concurrent with laser in situ keratomileusis. J Cataract Refract Surg . 2012 Aug;38(8):1424-31. Editors’ note: Dr. Lim has no financial interests related to her comments.