Re-evaluating the Effectiveness of Corneal Collagen Cross-Linking and Its True Biomechanical Effect in Human Eyes

  • Damien Gatinel
  • Cheryl MacGregor
  • Muhammed Jawad


Corneal collagen cross-linking (CXL), a technique where by corneal rigidity is thought to be increased through a photo polymerization reaction that results in the subsequent induction of cross-links between collagen fibres in corneal tissue, is a treatment option for keratoconus and other corneal ectasias that, in theory, addresses the underlying pathogenesis of the disease and has thus far shown to be a promising early treatment option for these conditions. However, a striking discrepancy exists between the reported biomechanical effects of CXL in vitro and the biomechanical effects of CXL in vivo, and this has not received much attention in the literature.

Despite a documented increase in corneal stiffness in vitro reported by many investigators, reports that provide evidence of measurable and consistent biomechanical change in corneal rigidity in vivo after CXL are not comparable. The absence of documented in vivo biomechanical improvement in CXL-treated corneas is a conundrum, which merits further consideration. In order to understand this discrepancy, it has been postulated that biomechanical changes induced by CXL are too subtle to be measured by the current diagnostic tools available or have characteristics not discernible to these technologies. However, the dynamic bidirectional applanation device (ORA) and dynamic Scheimpflug analyser instruments (Corvis ST) have demonstrated the ability to quantify even subtle biomechanical differences in untreated keratoconus corneas of differing ectatic degree, and document the reduction in corneal hysteresis (CH) and corneal resistance factor (CRF) in situations where the corneal stiffness is reduced, such as after laser in situ keratomileusis and surface ablation procedures. It has also been possible to demonstrate a reduced CH and CRF in patients with diabetes, smoking, glaucoma, Fuchs’ dystrophy, and corneal oedema. It is puzzling that these diagnostic tools are able to determine subtle biomechanical changes in these situations, yet fail to measure the purported change induced by CXL on corneas with progressive keratoconus. This failure to document significant and consistent biomechanical changes in corneal rigidity could suggest that CXL does not induce a simple reversal of the particular biomechanical deficits seen in keratoconus and that CXL does not make the cornea significantly more resistant to bending forces as has been previously postulated and is widely accepted. The absence of measurable biomechanical change in keratoconic corneas after CXL could be a consequence that the biomechanical strengthening that occurs, which in contrast to the marked weakening caused by pre-existing alteration of the collagen structure, disorganization of collagen fibre intertwining, and compromised structural–mechanical homogeneity that are hallmarks of keratoconic disease and are more pronounced in corneas with progressive keratoconus, is insignificant by comparison.

The changes in the cornea induced by CXL that have been described in vivo may instead be driven by a wound healing process in response to the removal of the corneal epithelial layer and subsequent exposure to riboflavin and ultraviolet-A. This paper will present evidence that upholds this hypothesis.


Crosslinking Corneal biomechanics Keratoconus Hysteresis Ectasia Corneal epithelium 


  1. 1.
    Spoerl E, Huhle M, Seiler T. Induction of cross-links in corneal tissue. Exp Eye Res. 1998;66(1):97–103.PubMedPubMedCentralCrossRefGoogle Scholar
  2. 2.
    Spoerl E, Seiler T. Techniques for stiffening the cornea. J Refract Surg. 1999;15(6):711–3.PubMedPubMedCentralGoogle Scholar
  3. 3.
    Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-A-induced collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol. 2003;135(5):620–7.CrossRefGoogle Scholar
  4. 4.
    Kohlhaas M, Spoerl E, Speck A, Schilde T, Sandner D, Pillunat LE. A new treatment of keratectasia after LASIK by using collagen with riboflavin/UVA light cross-linking. Klin Monatsbl Augenheilkd. 2005;222(5):430–6.PubMedCrossRefGoogle Scholar
  5. 5.
    Luce D. Determining in vivo biomechanical properties of the cornea with an ocular response analyzer. J Cataract Refract Surg. 2005;31:156–62.PubMedCrossRefGoogle Scholar
  6. 6.
    Shah S, Laiquzzaman M, Bhojwani R, Mantry S, Cunliffe I. Assessment of the biomechanical properties of the cornea with the ocular response analyzer in normal and keratoconic eyes. Invest Ophthalmol Vis Sci. 2007;48(7):3026–31.PubMedCrossRefGoogle Scholar
  7. 7.
    Saad A, Lteif Y, Azan E, Gatinel D. Biomechanical properties of keratoconus suspect eyes. Invest Ophthalmol Vis Sci. 2010;51(6):2912–6.PubMedCrossRefGoogle Scholar
  8. 8.
    Ali NQ, Patel DV, McGhee CN. Biomechanical responses of healthy and keratoconic corneas measured using a non-contact Scheimpflug-based tonometer. Invest Ophthalmol Vis Sci. 2014;55:3651–9.PubMedCrossRefGoogle Scholar
  9. 9.
    del Buey MA, Cristóbal JA, Ascaso FJ, Lavilla L, Lanchares E. Biomechanical properties of the cornea in Fuchs’ corneal dystrophy. Invest Ophthalmol Vis Sci. 2009;50(7):3199–202.PubMedCrossRefGoogle Scholar
  10. 10.
    Prata TS, Lima VC, De Moraes CG, et al. Factors associated with topographic changes of the optic nerve head induced by acute intraocular pressure reduction in glaucoma patients. Eye (Lond). 2011;25:201–7.CrossRefGoogle Scholar
  11. 11.
    Deol M, Taylor DA, Radcliffe NM. Corneal hysteresis and its relevance to glaucoma. Curr Opin Ophthalmol. 2015;26(2):96–102.PubMedPubMedCentralCrossRefGoogle Scholar
  12. 12.
    Beene LC, Traboulsi EI, Seven I, Ford MR, Sinha Roy A, Butler RS, Dupps WJ Jr. Corneal deformation response and ocular geometry: a noninvasive diagnostic strategy in Marfan syndrome. Am J Ophthalmol. 2016;161:56–64.e1.PubMedCrossRefGoogle Scholar
  13. 13.
    Chen S, Chen D, Wang J, Lu F, Wang Q, Qu J. Changes in ocular response analyzer parameters after LASIK. J Refract Surg. 2010;26(4):279–88.PubMedCrossRefGoogle Scholar
  14. 14.
    Koprowski R. Automatic method of analysis and measurement of additional parameters of corneal deformation in the Corvis tonometer. Biomed Eng Online. 2014;13:150.PubMedPubMedCentralCrossRefGoogle Scholar
  15. 15.
    Goldich Y, Barkana Y, Morad Y, Hartstein M, Avni I, Zadok D. Can we measure corneal biomechanical changes after collagen cross-linking in eyes with keratoconus?-a pilot study. Cornea. 2009;28(5):498–502.PubMedCrossRefGoogle Scholar
  16. 16.
    Sedaghat M, Naderi M, Zarei-Ghanavati M. Biomechanical parameters of the cornea after collagen crosslinking measured by waveform analysis. J Cataract Refract Surg. 2010;36(10):1728–31.PubMedCrossRefGoogle Scholar
  17. 17.
    Gkika MG, Labiris G, Kozobolis VP. Tonometry in keratoconic eyes before and after riboflavin/UVA corneal collagen crosslinking using three different tonometers. Eur J Ophthalmol. 2012;22(2):142–52.PubMedCrossRefGoogle Scholar
  18. 18.
    De Bernardo M, Capasso L, Lanza M, Tortori A, Iaccarino S, Cennamo M, Borrelli M, Rosa N. Long-term results of corneal collagen crosslinking for progressive keratoconus. J Optom. 2015;8(3):180–6.PubMedCrossRefGoogle Scholar
  19. 19.
    Spoerl E, Terai N, Scholz F, Raiskup F, Pillunat LE. Detection of biomechanical changes, after corneal cross-linking using ocular response analyzer software. J Refract Surg. 2011;27(6):452–7.PubMedCrossRefGoogle Scholar
  20. 20.
    Kiliç A, Roberts CJ. Biomechanical and refractive results of transepithelial cross linking treatment in keratoconic eyes. Int J Kerat Ect Cor Dis. 2012;1(2):75–8.Google Scholar
  21. 21.
    Vinciguerra P, Albè E, Trazza S, Rosetta P, Vinciguerra R, Seiler T, Epstein D. Refractive, topographic, tomographic, and aberrometric analysis of keratoconic eyes undergoing corneal crosslinking. Ophthalmology. 2009;116(3):369–78.PubMedPubMedCentralCrossRefGoogle Scholar
  22. 22.
    Lanza M, Cennamo M, Iaccarino S, Irregolare C, Rechichi M, Bifani, Gironi Carnevale AU. Evaluation of corneal deformation analyzed with Scheimpflug based device in healthy eyes and diseased ones. BioMed Res Int. 2014;2014:748671. 9 pages.PubMedPubMedCentralCrossRefGoogle Scholar
  23. 23.
    Bak-Nielsen S, Pedersen IB, Ivarsen A, Hjortdal J. Dynamic Scheimpflug-based assessment of keratoconus and the effects of corneal cross-linking. J Refract Surg. 2014;30(6):408–14.PubMedCrossRefGoogle Scholar
  24. 24.
    Tomita M, Mita M, Huseynova T. Accelerated versus conventional corneal collagen crosslinking. J Cataract Refract Surg. 2014;40:1013–20.PubMedPubMedCentralCrossRefGoogle Scholar
  25. 25.
    Scheler A, Spoerl E, Boehm AG. Effect of diabetes mellitus on corneal biomechanics and measurement of intraocular pressure. Acta Ophthalmol. 2012;90(6):e447–51.PubMedCrossRefGoogle Scholar
  26. 26.
    Schweitzer C, Korobelnik JF, Boniol M, Cougnard-Gregoire A, Le Goff M, Malet F, Rougier MB, Delyfer MN, Dartigues JF, Delcourt C. Associations of biomechanical properties of the cornea with environmental and metabolic factors in an elderly population: the ALIENOR Study. Invest Ophthalmol Vis Sci. 2016;57(4):2003–11.PubMedCrossRefGoogle Scholar
  27. 27.
    Kilavuzoglu AE, Celebi AR, Altiparmak UE, Cosar CB. The effect of smoking on corneal biomechanics. Curr Eye Res. 2017;42(1):16–20.PubMedCrossRefGoogle Scholar
  28. 28.
    Spörl E, Terai N, Haustein M, Böhm AG, Raiskup-Wolf F, Pillunat LE. Biomechanical condition of the cornea as a new indicator for pathological and structural changes. Ophthalmologe. 2009;106(6):512–20.PubMedCrossRefGoogle Scholar
  29. 29.
    Qazi MA, Sanderson JP, Mahmoud AM, Yoon EY, Roberts CJ, Pepose JS. Postoperative changes in intraocular pressure and corneal biomechanical metrics Laser in situ keratomileusis versus laser-assisted subepithelial keratectomy. J Cataract Refract Surg. 2009;35(10):1774–88.PubMedCrossRefGoogle Scholar
  30. 30.
    Kamiya K, Shimizu K, Ohmoto F. Comparison of the changes in corneal biomechanical properties after photorefractive keratectomy and laser in situ keratomileusis. Cornea. 2009;28(7):765–9.PubMedCrossRefGoogle Scholar
  31. 31.
    Kamiya K, Shimizu K, Ohmoto F. Time course of corneal biomechanical parameters after laser in situ keratomileusis. Ophthalmic Res. 2009;42(3):167–71.PubMedCrossRefGoogle Scholar
  32. 32.
    Barbara R, Nassar A, Zadok D, Barbara A. Corneal biomechanical properties post-LASEK for the correction of myopia. Int K Kerat Ect Cor Dis. 2014;3(1):23–6.Google Scholar
  33. 33.
    Pedersen IB, Bak-Nielsen S, Vestergaard AH, Ivarsen A, Hjortdal J. Corneal biomechanical properties after LASIK, ReLEx flex, and ReLEx smile by Scheimpflug-based dynamic tonometry. Graefes Arch Clin Exp Ophthalmol. 2014;252(8):1329–35.PubMedCrossRefGoogle Scholar
  34. 34.
    Gatinel D. Eye rubbing, a sine qua non for keratoconus? Int J Kerat Ect Cor Dis. 2016;5(1):6–12.Google Scholar
  35. 35.
    Smolek MK, Klyce SD. Is keratoconus a true ectasia? An evaluation of corneal surface area. Arch Ophthalmol. 2000;118(9):1179–86.PubMedCrossRefGoogle Scholar
  36. 36.
    Nguyen TM, Aubry JF, Fink M, Bercoff J, Tanter M. In vivo evidence of porcine cornea anisotropy using supersonic shear wave imaging. Invest Ophthalmol Vis Sci. 2014.28;55(11):7545–52.PubMedCrossRefGoogle Scholar
  37. 37.
    Touboul D, Gennisson JL, Nguyen TM, Robinet A, Roberts CJ, Tanter M, Grenier N. Supersonic shear wave elastography for the in vivo evaluation of transepithelial corneal collagen cross-linking. Invest Ophthalmol Vis Sci. 2014.28;55(3):1976–84.PubMedCrossRefGoogle Scholar
  38. 38.
    Gatinel D. Effectiveness of corneal collagen crosslinking in vivo for corneal stiffening. J Cataract Refract Surg. 2014;40(11):1943–4.PubMedPubMedCentralCrossRefGoogle Scholar
  39. 39.
    Goldich Y, Marcovich AL, Barkana Y, et al. Clinical and corneal biomechanical changes after collagen cross-linking with riboflavin and UV irradiation in patients with progressive keratoconus: results after 2 years of follow-up. Cornea. 2012;31:609–14.PubMedPubMedCentralCrossRefGoogle Scholar
  40. 40.
    Raiskup-Wolf F, Hoyer A, Spoerl E, Pillunat LE. Collagen crosslinking with riboflavin and ultraviolet-A light in keratoconus: long-term results. J Cataract Refract Surg. 2008;34:796–801.CrossRefPubMedGoogle Scholar
  41. 41.
    Vinciguerra P, Albè E, Frueh BE, Trazza S, Epstein D. Two-year corneal cross-linking results in patients younger than 18 years with documented progressive keratoconus. Am J Ophthalmol. 2012;154:520–6.CrossRefPubMedGoogle Scholar
  42. 42.
    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;149:585–93.CrossRefPubMedGoogle Scholar
  43. 43.
    Greenstein SA, Fry KL, Hersh PS. Corneal topography indices after corneal collagen crosslinking for keratoconus and corneal ectasia: one-year results. J Cataract Refract Surg. 2011;37(7):1282–90.CrossRefPubMedGoogle Scholar
  44. 44.
    Greenstein SA, Fry KL, Hersh MJ, Hersh PS. Higher-order aberrations after corneal collagen crosslinking for keratoconus and corneal ectasia. J Cataract Refract Surg. 2012;38(2):292–302.PubMedCrossRefGoogle Scholar
  45. 45.
    Guilbert E, Saad A, Elluard M, Grise-Dulac A, Rouger H, Gatinel D. Repeatability of keratometry measurements obtained with three topographers in keratoconic and normal corneas. J Refract Surg. 2016;32(3):187–92.PubMedCrossRefGoogle Scholar
  46. 46.
    Shalchi Z, Wang X, Nanavaty MA. Safety and efficacy of epithelium removal and transepithelial corneal collagen crosslinking for keratoconus. Eye (Lond). 2015;29(1):15–29.CrossRefGoogle Scholar
  47. 47.
    Starr M, Donnenfeld E, Newton M, Tostanoski J, Muller J, Odrich M. Excimer laser phototherapeutic keratectomy. Cornea. 1996;15:557–65.PubMedCrossRefGoogle Scholar
  48. 48.
    Vinciguerra P, Romano V, Rosetta P, Legrottaglie EF, Piscopo R, Fabiani C, Azzolini C, Vinciguerra R. Transepithelial iontophoresis versus standard corneal collagen cross-linking: 1-year results of a prospective clinical study. J Refract Surg. 2016;32(10):672–8.PubMedPubMedCentralCrossRefGoogle Scholar
  49. 49.
    Stojanovic A, Chen X, Jin N, Zhang T, Stojanovic F, Raeder S, et al. Safety and efficacy of epithelium-on corneal collagen cross-linking using a multifactorial approach to achieve proper stromal riboflavin saturation. J Ophthalmol. 2012;2012:498435.PubMedPubMedCentralCrossRefGoogle Scholar
  50. 50.
    Filippello M, Stagni E, O'Brart D. Transepithelial corneal collagen crosslinking: bilateral study. J Cataract Refract Surg. 2012;38(2):283–91.PubMedCrossRefGoogle Scholar
  51. 51.
    Salah-Mabed I, Saad A, Gatinel D. Topography of the corneal epithelium and Bowman layer in low to moderately myopic eyes. J Cataract Refract Surg. 2016;42(8):1190–7.PubMedCrossRefGoogle Scholar
  52. 52.
    Touboul D, Trichet E, Binder PS, Praud D, Seguy C, Colin J. Comparison of front-surface corneal topography and Bowman membrane specular topography in keratoconus. J Cataract Refract Surg. 2012;38(6):1043–9.PubMedCrossRefGoogle Scholar
  53. 53.
    Sykakis E, Karim R, Evans JR, Bunce C, Amissah-Arthur KN, Patwary S, McDonnell PJ, Hamada S. Corneal collagen cross-linking for treating keratoconus. Cochrane Database Syst Rev. 2015;(3):CD010621.Google Scholar
  54. 54.
    Bennie HJ, Marjan F, Patel SV, Schwab IR. Corneal cross-linking for keratoconus: a look at the data, the Food and Drug Administration, and the future. Ophthalmology. 2016;123(11):2270–2.CrossRefGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Damien Gatinel
    • 1
  • Cheryl MacGregor
    • 1
  • Muhammed Jawad
    • 2
  1. 1.Ophthalmology DepartmentQueen Alexandra HospitalPortsmouthUK
  2. 2.Ophthalmology DepartmentNorth Hampshire HospitalBasingstokeUK

Personalised recommendations