Crosslinking und Keratokonus

Zusammenfassung

Ein Keratokonus führt zu einer progressiven Vorwölbung und Verdünnung der Hornhaut. Um dies aufzuhalten, kann ein Crosslinking durchgeführt werden. Dabei ist eine Behandlung nach dem „Dresdener Protokoll“ eine effektive und sichere Behandlungsmöglichkeit, aber auch zahlreiche neue Anwendungsprotokolle (akzeleriertes Crosslinking, transepitheliales Crosslinking) und sogar weitere Indikationen (refraktive Eingriffe, infektiöse Keratitis) wurden in den letzten Jahren veröffentlicht.

Abstract

Keratoconus leads to a progressive protrusion and thinning of the cornea. In order to stop this, corneal crosslinking can be performed if the progression of the disease is proven. Crosslinking according to the “Dresden protocol” includes abrasion of the corneal epithelium, application of riboflavin eye drops and irradiation with UV-A light of an intensity of 3 mW/cm² for 30 minutes. The efficacy has been shown in several prospective randomized studies. One of the more recent developments is accelerated crosslinking, which allows a shorter irradiation time. On the other hand, the possibility of transepithelial crosslinking was presented, which does not require an abrasion of the cornea. This should reduce the occurrence of postoperative pain. The range of indications has also been expanded. Corneal crosslinking is used for post-LASIK keratectasia as well. It is also being considered for use in infectious keratitis. Topographically controlled crosslinking can likewise be used to try to positively influence the refractive power of the cornea. The risks of crosslinking include the occurrence of pain, haze or scarring, endothelial cell damage and, rarely, the occurrence of keratitis.

Kernaussagen

• Der Keratokonus führt zu einer fortschreitenden Vorwölbung und Verdünnung der Hornhaut. Um dies aufzuhalten, kann bei nachgewiesener Progression der Erkrankung ein Crosslinking durchgeführt werden.

• Das Crosslinking nach dem „Dresdener Protokoll“ umfasst die Abrasio des Hornhautepithels, die Applikation von Riboflavin-Augentropfen und die Bestrahlung mit UV-A-Licht einer Intensität von 3 mW/cm² über 30 min. Die Wirksamkeit wurde in mehreren prospektiven randomisierten Studien gezeigt.

• Zu den neueren Entwicklungen zählt zum einen das akzelerierte Crosslinking, bei dem eine kürzere Bestrahlungszeit möglich ist.

• Zum anderen wurde die Möglichkeit des transepithelialen Crosslinking präsentiert, bei dem eine Abrasio der Hornhaut nicht durchgeführt werden muss. Dieses Vorgehen soll das Auftreten von postoperativen Schmerzen reduzieren.

• Auch das Indikationsspektrum hat sich erweitert: Korneales Crosslinking wird auch bei Keratektasie nach LASIK eingesetzt. Ebenso wird die Anwendung bei der infektiösen Keratitis erwogen.

• Durch topografiegesteuertes Crosslinking kann versucht werden, die Brechkraft der Hornhaut positiv zu beeinflussen.

• Zu den Risiken des Crosslinking zählen

  • das Auftreten von Schmerzen,

  • Haze- bzw. Narbenbildung,

  • Endothelzellschäden und

  • selten das Auftreten einer Keratitis.

Schlüsselwörter

Keratokonus - Crosslinking - Kornea

Key words

keratoconus - crosslinking - cornea

Publikationsverlauf

Artikel online veröffentlicht:
19. April 2021

• Literatur

• 1 Krachmer JH, Feder RS, Belin MW. Keratoconus and related noninflammatory corneal thinning disorders. Surv Ophthalmol 1984; 28: 293-322
• 2 Shapiro MB, France TD. The ocular features of Downʼs syndrome. Am J Ophthalmol 1985; 99: 659-663
• 3 Bawazeer A, Hodge W, Lorimer B. Atopy and keratoconus: a multivariate analysis. Br J Ophthalmol 2000; 84: 834-836 doi:10.1136/bjo.84.8.834
• 4 McMonnies CW. Mechanisms of rubbing-related corneal trauma in keratoconus. Cornea 2009; 28: 607-615 doi:10.1097/ICO.0b013e318198384f
• 5 Hollingsworth JG, Efron N. Observations of banding patterns (Vogt striae) in keratoconus: a confocal microscopy study. Cornea 2005; 24: 162-166 doi:10.1097/01.ico.0000141231.03225.d8
• 6 Zadnik K, Barr JT, Edrington TB. et al. Baseline findings in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. Invest Ophthalmol Vis Sci 1998; 39: 2537-2546
• 7 Lee YW, Choi CY, Yoon GY. Comparison of dual rotating Scheimpflug-Placido, swept-source optical coherence tomography, and Placido-scanning-slit systems. J Cataract Refract Surg 2015; 41: 1018-1029 doi:10.1016/j.jcrs.2014.08.040
• 8 Heidari Z, Mohammadpour M, Hashemi H. et al. Early diagnosis of subclinical keratoconus by wavefront parameters using Scheimpflug, Placido and Hartmann-Shack based devices. Int Ophthalmol 2020; 40: 1659-1671 doi:10.1007/s10792-020-01334-3
• 9 Imbornoni LM, McGhee CNJ, Belin MW. Evolution of Keratoconus: From Diagnosis to Therapeutics. Klin Monbl Augenheilkd 2018; 235: 680-688 doi:10.1055/s-0044-100617
• 10 Duncan JK, Belin MW, Borgstrom M. Assessing progression of keratoconus: novel tomographic determinants. Eye Vis (Lond) 2016; 3: 6 doi:10.1186/s40662-016-0038-6
• 11 Kamiya K, Ishii R, Shimizu K. et al. Evaluation of corneal elevation, pachymetry and keratometry in keratoconic eyes with respect to the stage of Amsler-Krumeich classification. Br J Ophthalmol 2014; 98: 459-463 doi:10.1136/bjophthalmol-2013-304132
• 12 Belin MW, Duncan JK. Keratoconus: Das ABCD-System zur Stadieneinteilung. Klin Monbl Augenheilkd 2016; 233: 701-707 doi:10.1055/s-0042-100626
• 13 Downie LE, Lindsay RG. Contact lens management of keratoconus. Clin Exp Optom 2015; 98: 299-311 doi:10.1111/cxo.12300
• 14 Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-a-induced collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol 2003; 135: 620-627
• 15 Boxer Wachler BS, Christie JP, Chandra NS. et al. Intacs for keratoconus. Ophthalmology 2003; 110: 1031-1040
• 16 Bedi R, Touboul D, Pinsard L. et al. Refractive and topographic stability of Intacs in eyes with progressive keratoconus: five-year follow-up. J Refract Surg 2012; 28: 392-396 doi:10.3928/1081597X-20120509-01
• 17 Vega-Estrada A, Alió JL, Plaza-Puche AB. Keratoconus progression after intrastromal corneal ring segment implantation in young patients: Five-year follow-up. J Cataract Refract Surg 2015; 41: 1145-1152 doi:10.1016/j.jcrs.2014.08.045
• 18 Lang SJ, Bischoff M, Böhringer D. et al. Analysis of the changes in keratoplasty indications and preferred techniques. PLoS One 2014; 9: e112696 doi:10.1371/journal.pone.0112696
• 19 Basu S, Reddy JC, Vaddavalli PK. et al. Long-term outcomes of penetrating keratoplasty for keratoconus with resolved corneal hydrops. Cornea 2012; 31: 615-620 doi:10.1097/ICO.0b013e31823d03e3
• 20 Lang SJ, Richter C, Richter O. et al. Keratoplastik im Kindes- und Jugendalter. Klin Monbl Augenheilkd 2017; DOI: 10.1055/s-0042-124512.
• 21 Godefrooij DA, Gans R, Imhof SM. et al. Nationwide reduction in the number of corneal transplantations for keratoconus following the implementation of cross-linking. Acta Ophthalmol 2016; 94: 675-678 doi:10.1111/aos.13095
• 22 Spoerl E, Huhle M, Seiler T. Induction of cross-links in corneal tissue. Exp Eye Res 1998; 66: 97-103 doi:10.1006/exer.1997.0410
• 23 Wollensak G, Spoerl E, Reber F. et al. Keratocyte cytotoxicity of riboflavin/UVA-treatment in vitro. Eye (Lond) 2004; 18: 718-722 doi:10.1038/sj.eye.6700751
• 24 Wollensak G, Spoerl E, Wilsch M. et al. Endothelial cell damage after riboflavin-ultraviolet-A treatment in the rabbit. Journal of Cataract & Refractive Surgery 2003; 29: 1786-1790 doi:10.1016/S0886-3350(03)00343-2
• 25 Wittig-Silva C, Whiting M, Lamoureux E. et al. A randomized controlled trial of corneal collagen cross-linking in progressive keratoconus: preliminary results. J Refract Surg 2008; 24: S720-S725
• 26 Wittig-Silva C, Chan E, Islam FMA. et al. A randomized, controlled trial of corneal collagen cross-linking in progressive keratoconus: three-year results. Ophthalmology 2014; DOI: 10.1016/j.ophtha.2013.10.028.
• 27 OʼBrart DPS, Chan E, Samaras K. et al. A randomised, prospective study to investigate the efficacy of riboflavin/ultraviolet A (370 nm) corneal collagen cross-linkage to halt the progression of keratoconus. Br J Ophthalmol 2011; 95: 1519-1524 doi:10.1136/bjo.2010.196493
• 28 Hersh PS, Greenstein SA, Fry KL. Corneal collagen crosslinking for keratoconus and corneal ectasia: One-year results. J Cataract Refract Surg 2011; 37: 149-160 doi:10.1016/j.jcrs.2010.07.030
• 29 Sykakis E, Karim R, Evans JR. et al. Corneal collagen cross-linking for treating keratoconus. Cochrane Database Syst Rev 2015; (03) CD010621 DOI: 10.1002/14651858.CD010621.pub2.
• 30 Sharma N, Suri K, Sehra SV. et al. Collagen cross-linking in keratoconus in Asian eyes: visual, refractive and confocal microscopy outcomes in a prospective randomized controlled trial. Int Ophthalmol 2015; DOI: 10.1007/s10792-015-0054-x.
• 31 Lang SJ, Messmer EM, Geerling G. et al. Prospective, randomized, double-blind trial to investigate the efficacy and safety of corneal cross-linking to halt the progression of keratoconus. BMC Ophthalmol 2015; 15: 78 doi:10.1186/s12886-015-0070-7
• 32 Hersh PS, Stulting RD, Muller D. et al. U.S. multicenter clinical trial of corneal collagen crosslinking for treatment of corneal ectasia after refractive surgery. Ophthalmology 2017; 124: 1475-1484 doi:10.1016/j.ophtha.2017.05.036
• 33 Seyedian MA, Aliakbari S, Miraftab M. et al. Corneal collagen cross-linking in the treatment of progressive keratoconus: a randomized controlled contralateral eye study. Middle East Afr J Ophthalmol 2015; 22: 340-345 doi:10.4103/0974-9233.159755
• 34 Wagner H, Barr JT, Zadnik K. collaborative longitudinal evaluation of keratoconus (CLEK) study: methods and findings to date. Cont Lens Anterior Eye 2007; 30: 223-232 doi:10.1016/j.clae.2007.03.001
• 35 Gemeinsamer Bundesausschuss. UV-Vernetzung mit Riboflavin bei Keratokonus. Abschlussbericht. 2018. Im Internet (Stand: 23.05.2020): https://www.g-ba.de/downloads/40-268-5138/2018-07-19_MVV-RL_UV-Vernetzung-Riboflavin-Keratokonus_ZD.pdf
• 36 Moore JE, Schiroli D, Moore CBT. Potential effects of corneal cross-linking upon the limbus. Biomed Res Int 2016; 2016 DOI: 10.1155/2016/5062064.
• 37 Rosenblat E, Hersh PS. Intraoperative corneal thickness change and clinical outcomes after corneal collagen crosslinking: Standard crosslinking versus hypotonic riboflavin. J Cataract Refract Surg 2016; 42: 596-605 doi:10.1016/j.jcrs.2016.01.040
• 38 Soeters N, Hendriks I, Godefrooij DA. et al. Prospective 3-arm study on pain and epithelial healing after corneal crosslinking. J Cataract Refract Surg 2020; 46: 72-77 doi:10.1016/j.jcrs.2019.08.036
• 39 Serna-Ojeda JC, Santana-Cruz O, Quiroz-Casian N. et al. Pain management in corneal collagen crosslinking for keratoconus: a comparative case series. J Ocul Pharmacol Ther 2019; 35: 325-330 doi:10.1089/jop.2019.0021
• 40 Flach AJ. Corneal melts associated with topically applied nonsteroidal anti-inflammatory drugs. Trans Am Ophthalmol Soc 2001; 99: 205-210 discussion 210–212
• 41 Wolf EJ, Kleiman LZ, Schrier A. Nepafenac-associated corneal melt. J Cataract Refract Surg 2007; 33: 1974-1975 doi:10.1016/j.jcrs.2007.06.043
• 42 Greenstein SA, Fry KL, Bhatt J. et al. Natural history of corneal haze after collagen crosslinking for keratoconus and corneal ectasia: Scheimpflug and biomicroscopic analysis. J Cataract Refract Surg 2010; 36: 2105-2114 doi:10.1016/j.jcrs.2010.06.067
• 43 Sachdev GS, Sachdev M. Recent advances in corneal collagen cross-linking. Indian J Ophthalmol 2017; 65: 787-796 doi:10.4103/ijo.IJO_648_17
• 44 Kamaev P, Friedman MD, Sherr E. et al. Photochemical kinetics of corneal cross-linking with riboflavin. Invest Ophthalmol Vis Sci 2012; 53: 2360-2367 doi:10.1167/iovs.11-9385
• 45 Shajari M, Kolb CM, Agha B. et al. Comparison of standard and accelerated corneal cross-linking for the treatment of keratoconus: a meta-analysis. Acta Ophthalmologica 2019; 97: e22-e35 doi:10.1111/aos.13814
• 46 Rubinfeld RS, Caruso C, Ostacolo C. Corneal cross-linking: the science beyond the myths and misconceptions. Cornea 2019; 38: 780-790 doi:10.1097/ICO.0000000000001912
• 47 Richoz O, Hammer A, Tabibian D. et al. The biomechanical effect of corneal collagen cross-linking (CXL) with riboflavin and UV-A is oxygen dependent. Transl Vis Sci Technol 2013; 2: 6 doi:10.1167/tvst.2.7.6
• 48 Shetty R, Pahuja NK, Nuijts RMMA. et al. Current protocols of corneal collagen cross-linking: visual, refractive, and tomographic outcomes. Am J Ophthalmol 2015; 160: 243-249 doi:10.1016/j.ajo.2015.05.019
• 49 Mazzotta C, Traversi C, Paradiso AL. et al. Pulsed light accelerated crosslinking versus continuous light accelerated crosslinking: one-year results. J Ophthalmol 2014; 2014 DOI: 10.1155/2014/604731.
• 50 Moramarco A, Iovieno A, Sartori A. et al. Corneal stromal demarcation line after accelerated crosslinking using continuous and pulsed light. J Cataract Refract Surg 2015; 41: 2546-2551 doi:10.1016/j.jcrs.2015.04.033
• 51 Peyman A, Nouralishahi A, Hafezi F. et al. Stromal demarcation line in pulsed versus continuous light accelerated corneal cross-linking for keratoconus. J Refract Surg 2016; 32: 206-208 doi:10.3928/1081597X-20160204-03
• 52 Li Y, Tan O, Brass R. et al. Corneal epithelial thickness mapping by Fourier-domain optical coherence tomography in normal and keratoconic eyes. Ophthalmology 2012; 119: 2425-2433 doi:10.1016/j.ophtha.2012.06.023
• 53 Farquhar MG, Palade GE. Junctional complexes in various epithelia. J Cell Biol 1963; 17: 375-412 doi:10.1083/jcb.17.2.375
• 54 Pérez-Santonja JJ, Artola A, Javaloy J. et al. Microbial keratitis after corneal collagen crosslinking. J Cataract Refract Surg 2009; 35: 1138-1140 doi:10.1016/j.jcrs.2009.01.036
• 55 Hayes S, OʼBrart DP, Lamdin LS. et al. Effect of complete epithelial debridement before riboflavin-ultraviolet-A corneal collagen crosslinking therapy. J Cataract Refract Surg 2008; 34: 657-661 doi:10.1016/j.jcrs.2008.02.002
• 56 Al Fayez MF, Alfayez S, Alfayez Y. Transepithelial versus epithelium-off corneal collagen cross-linking for progressive keratoconus: a prospective randomized controlled trial. Cornea 2015; 34 Suppl 10: S53-S56 doi:10.1097/ICO.0000000000000547
• 57 Mastropasqua L, Nubile M, Lanzini M. et al. Morphological modification of the cornea after standard and transepithelial corneal cross-linking as imaged by anterior segment optical coherence tomography and laser scanning in vivo confocal microscopy. Cornea 2013; 32: 855-861 doi:10.1097/ICO.0b013e3182844c60
• 58 Kissner A, Spoerl E, Jung R. et al. Pharmacological modification of the epithelial permeability by benzalkonium chloride in UVA/Riboflavin corneal collagen cross-linking. Curr Eye Res 2010; 35: 715-721 doi:10.3109/02713683.2010.481068
• 59 Raiskup F, Pinelli R, Spoerl E. Riboflavin osmolar modification for transepithelial corneal cross-linking. Curr Eye Res 2012; 37: 234-238 doi:10.3109/02713683.2011.637656
• 60 Li W, Wang B. Efficacy and safety of transepithelial corneal collagen crosslinking surgery versus standard corneal collagen crosslinking surgery for keratoconus: a meta-analysis of randomized controlled trials. BMC Ophthalmol 2017; 17: 262 doi:10.1186/s12886-017-0657-2
• 61 Spadea L, Mencucci R. Transepithelial corneal collagen cross-linking in ultrathin keratoconic corneas. Clin Ophthalmol 2012; 6: 1785-1792 doi:10.2147/OPTH.S37335
• 62 Alhamad TA, OʼBrart DPS, OʼBrart NAL. et al. Evaluation of transepithelial stromal riboflavin absorption with enhanced riboflavin solution using spectrophotometry. J Cataract Refract Surg 2012; 38: 884-889 doi:10.1016/j.jcrs.2011.11.049
• 63 Caporossi A, Mazzotta C, Paradiso AL. et al. Transepithelial corneal collagen crosslinking for progressive keratoconus: 24-month clinical results. J Cataract Refract Surg 2013; 39: 1157-1163 doi:10.1016/j.jcrs.2013.03.026
• 64 Soeters N, Wisse RPL, Godefrooij DA. et al. Transepithelial versus epithelium-off corneal cross-linking for the treatment of progressive keratoconus: a randomized controlled trial. Am J Ophthalmol 2015; 159: 821-828.e3 doi:10.1016/j.ajo.2015.02.005
• 65 Lombardo M, Serrao S, Rosati M. et al. Biomechanical changes in the human cornea after transepithelial corneal crosslinking using iontophoresis. J Cataract Refract Surg 2014; 40: 1706-1715 doi:10.1016/j.jcrs.2014.04.024
• 66 Vinciguerra P, Rosetta P, Legrottaglie EF. et al. Iontophoresis CXL with and without epithelial debridement versus standard CXL: 2-year clinical results of a prospective clinical study. J Refract Surg 2019; 35: 184-190 doi:10.3928/1081597X-20190128-01
• 67 Kanellopoulos AJ, Dupps WJ, Seven I. et al. Toric topographically customized transepithelial, pulsed, very high-fluence, higher energy and higher riboflavin concentration collagen cross-linking in keratoconus. Case Rep Ophthalmol 2014; 5: 172-180 doi:10.1159/000363371
• 68 Dhawan S, Rao K, Natrajan S. Complications of corneal collagen cross-linking. J Ophthalmol 2011; 2011: 869015 doi:10.1155/2011/869015
• 69 Pollhammer M, Cursiefen C. Bacterial keratitis early after corneal crosslinking with riboflavin and ultraviolet-A. J Cataract Refract Surg 2009; 35: 588-589 doi:10.1016/j.jcrs.2008.09.029
• 70 Zamora KV, Males JJ. Polymicrobial keratitis after a collagen cross-linking procedure with postoperative use of a contact lens: a case report. Cornea 2009; 28: 474-476 doi:10.1097/ICO.0b013e31818d381a
• 71 Rama P, Di Matteo F, Matuska S. et al. Acanthamoeba keratitis with perforation after corneal crosslinking and bandage contact lens use. J Cataract Refract Surg 2009; 35: 788-791 doi:10.1016/j.jcrs.2008.09.035
• 72 Dhawan S, Rao K, Natrajan S. Complications of Corneal Collagen Cross-Linking. J Ophthalmol 2011; 2011: e869015 doi:10.1155/2011/869015
• 73 Kymionis GD, Portaliou DM, Bouzoukis DI. et al. Herpetic keratitis with iritis after corneal crosslinking with riboflavin and ultraviolet A for keratoconus. J Cataract Refract Surg 2007; 33: 1982-1984 doi:10.1016/j.jcrs.2007.06.036
• 74 Mazzotta C, Balestrazzi A, Traversi C. et al. Treatment of progressive keratoconus by riboflavin-UVA-induced cross-linking of corneal collagen: ultrastructural analysis by Heidelberg Retinal Tomograph II in vivo confocal microscopy in humans. Cornea 2007; 26: 390-397 doi:10.1097/ICO.0b013e318030df5a
• 75 Elling M, Kersten-Gomez I, Dick HB. Photorefractive intrastromal corneal crosslinking for treatment of myopic refractive error: Findings from 12-month prospective study using an epithelium-off protocol. J Cataract Refract Surg 2018; 44: 487-495 doi:10.1016/j.jcrs.2018.01.022
• 76 Stodulka P, Halasova Z, Slovak M. et al. Photorefractive intrastromal crosslinking for correction of hyperopia: 12-month results. J Cataract Refract Surg 2020; 46: 434-440 doi:10.1097/j.jcrs.0000000000000074
• 77 Sachdev GS, Ramamurthy S, Dandapani R. Photorefractive intrastromal corneal crosslinking for treatment of low myopia: clinical outcomes using the transepithelial approach with supplemental oxygen. J Cataract Refract Surg 2020; 46: 428-433 doi:10.1097/j.jcrs.0000000000000073
• 78 Krueger RR, Dupps WJ. Biomechanical effects of femtosecond and microkeratome-based flap creation: prospective contralateral examination of two patients. J Refract Surg 2007; 23: 800-807
• 79 Comaish IF, Lawless MA. Progressive post-LASIK keratectasia: biomechanical instability or chronic disease process?. J Cataract Refract Surg 2002; 28: 2206-2213 doi:10.1016/s0886-3350(02)01698-x
• 80 Li G, Fan Z-J, Peng X-J. Corneal collagen crosslinking for corneal ectasia of post-LASIK: one-year results. Int J Ophthalmol 2012; 5: 190-195 doi:10.3980/j.issn.2222-3959.2012.02.15
• 81 Bonzano C, Di Zazzo A, Barabino S. et al. Collagen Cross-Linking in the Management of Microbial Keratitis. Ocul Immunol Inflamm 2019; 27: 507-512 doi:10.1080/09273948.2017.1414856
• 82 Tabibian D, Richoz O, Hafezi F. PACK-CXL: Corneal Cross-linking for Treatment of Infectious Keratitis. J Ophthalmic Vis Res 2015; 10: 77-80 doi:10.4103/2008-322X.156122
• 83 Bamdad S, Malekhosseini H, Khosravi A. Ultraviolet A/riboflavin collagen cross-linking for treatment of moderate bacterial corneal ulcers. Cornea 2015; 34: 402-406 doi:10.1097/ICO.0000000000000375
• 84 Wei A, Wang K, Wang Y. et al. Evaluation of corneal cross-linking as adjuvant therapy for the management of fungal keratitis. Graefes Arch Clin Exp Ophthalmol 2019; 257: 1443-1452 doi:10.1007/s00417-019-04314-1
• 85 Prajna NV, Radhakrishnan N, Lalitha P. et al. Cross-linking-assisted infection reduction: a randomized clinical trial evaluating the effect of adjuvant cross-linking on outcomes in fungal keratitis. Ophthalmology 2020; 127: 159-166 doi:10.1016/j.ophtha.2019.08.029
• 86 Papaioannou L, Miligkos M, Papathanassiou M. Corneal collagen cross-linking for infectious keratitis: a systematic review and meta-analysis. Cornea 2016; 35: 62-71 doi:10.1097/ICO.0000000000000644
• 87 del Buey MA, Cristóbal JA, Casas P. et al. Evaluation of in vitro efficacy of combined riboflavin and ultraviolet a for Acanthamoeba isolates. Am J Ophthalmol 2012; 153: 399-404 doi:10.1016/j.ajo.2011.07.025