STABILISATION OF CORNEOPLASTIC PROCEDURES

Although the corneoplastic effects of intra-corneal ring segment implantation generally remain stable for many years [1], CXL is being considered as a useful adjunct to the procedure to further stabilise the altered corneal shape. The development of this combination treatment is in its early stages and the optimal time to perform each stage of the treatment has yet to be ascertained [2,3]. Combining LASIK with CXL may result in improved corneal integrity and thereby reduce instances of post-LASIK keratectasia. Indeed, a recent study investigating this found that patients treated with combined LASIK and CXL had a similar or slightly better clinical outcome than those treated with LASIK alone [4].

 The use of CXL with topography-guided PRK was first described by Kanellopoulos and Binder [5]. Since then, Kymionis et al. [6] have shown that the simultaneous treatment of topography-guided PRK followed by CXL for keratoconus results in reduced refractive error and keratometry readings and improvements in visual acuity that remain stable at a mean follow-up of nearly 20 months. Similar results have been obtained by Stojanovic et al [7]. However, it is worth noting that in vitro studies of untreated and CXL treated pig corneas have shown that the efficacy of laser ablation is lower in CXL treated corneas [8] and so it may be necessary to modify existing ablation algorithms for the treatment of cross-linked corneas [8].

Further investigations into the use of CXL as a means of stabilising corneal moulding have produced mixed results. Early studies of accelerated CXL in combination with microwave keratoplasty, (a novel technique used to induce axial shrinkage of collagen and thereby flatten the keratoconus cornea), found it to be only minimally effective as an adjunct to the procedure as it failed to maintain the flattening effect and regression occurred [9]. When used in conjunction with orthokeratology it was found that CXL failed to stabilise the moulding effect (corneal topography and wave front error returned to baseline levels within 1 month of orthokeratology interruption) but nevertheless resulted in improved visual acuity, which remained above baseline levels 1 year after the combined treatment was performed [10].

[1] Bedi R, Touboul D, Pinsard L, Colin J. Refractive and topographic stability of Intacs in eyes with progressive keratoconus: five-year follow-up. Journal of Refractive Surgery. 2012;28(6):392-6.

[2] Ertan A, Karacal H, Kamburoglu G. Refractive and topographic results of transepithelial cross-linking treatment in eyes with Intacs. Cornea. 2009;28:719-23.

[3] Iovieno A, Légaré M, Rootman D, Yeung S, Kim P, Rootman D. Intracorneal ring segments implantation followed by same-day photorefractive keratectomy and corneal collagen cross-linking in keratoconus. Journal of Refractive Surgery. 2011;27(12):915-8.

[4] Celik H, Alagöz N, Yildirim Y, Agca A, Marshall J, Demirok A, et al. Accelerated corneal crosslinking concurrent with laser in situ keratomileusis. Journal of Cataract and Refractive Surgery. 2012;38(8):1424-31.

[5] Kanellopoulos A, Binder P. Collagen cross-linking (CCL) with sequential topography-guided PRK: a temporizing alternative for keratoconus to penetrating keratoplasty. Cornea. 2007;26:891-5.

[6] Kymionis G, Portaliou D, Kounis G, al e. Simultaneous topography-guided photorefractive keratectomy followed by corneal collagen cross-linking for keratoconus. American Journal of Ophthalmology. 2011;152:748-55.

[7] Stojanovic A, Zhang J, Chen X, Nitter T, Chen S, Wang Q. Topography-guided transepithelial surface ablation followed by corneal collagen cross-linking performed in a single combined procedure for the treatment of keratoconus and pellucid marginal degeneration. Journal of Refractive Surgery. 2010;26(2):145-52.

[8] Chen S, Li Y, Stojanovic A, Zhang J, Wang Y, Wang Q, et al. Evaluation of the efficacy of excimer laser ablation of cross-linked porcine cornea. PLoS One. 2012;7(10):e46232.

[9] Vega-Estrada A, Alió J, Plaza Puche A, Marshall J. Outcomes of a new microwave procedure followed by accelerated cross-linking for the treatment of keratoconus: a pilot study. Journal of Refractive Surgery. 2012;28(11):787-92.

[10] Calossi A, Romano F, Ferraioli G, Romano V. Orthokeratology and riboflavin-UVA corneal collagen cross-linking in keratoconus. Journal of Emmetropia. 2010;1:126-31.