Abstract
PurposeTo compare the outcomes of accelerated versus standard corneal cross-linking for the treatment of progressive keratoconus.Methods In this retrospective comparative study, 63 eyes of 40 patients with progressive keratoconus were divided into two groups; 27 eyes in group one were treated with an accelerated protocol (10 mW/cm, 9 min) and 36 eyes in group two were treated with the standard method (3 mW/cm, 30 min). Visual acuity, refraction, corneal topography, corneal tomography, and anterior and posterior corneal higher-order aberrations (HOAs) were assessed preoperatively and 18–30 months postoperatively.ResultsThe LogMAR uncorrected and corrected distance visual acuity values were improved in both groups postoperatively. However, the improvement was significantly higher in group one (P 0.05, all). The flattening in the anterior keratometry readings, flat K, steep K, and average K were significantly higher in group two (P 0.001, all). The maximum anterior keratometry (AKf) values significantly decreased in both groups, whereas the maximum posterior keratometry (AKb) values increased. The reduction in the minimum corneal thickness (ThKmin) was significantly greater (36.49um) in group two, compared to 10.85um in group one. There was a significant increase in the posterior average keratometry, and a significant decrease in the posterior astigmatism, along 3 mm meridian in S-CXL (P = 0.03, P = 0.008, respectively), while the corresponding values showed no statistical significance in group one (P 0.05). The anterior corneal trefoil was significantly reduced in group one (P = 0.002), whereas anterior total HOAs and coma were significantly improved in group two (P 0.0014, all). The posterior corneal spherical aberration decreased significantly in group one (P = 0.02), while group two revealed significant reduction in the posterior trefoil values (P = 0.011). The change in the anterior maximum keratometry was significantly and positively correlated to the preoperative maximum keratometry in group two (P = 0.53, P = 0.003).ConclusionAn accelerated cross-linking protocol using 10 mW/cm for 9 min showed more visual improvement and less pachymetric reduction when compared to the standard protocol, however, anterior corneal flattening, posterior corneal steepening, and the change in the posterior astigmatism were significantly higher in the standard protocol; while corneal HOAs were improved in both protocols.
Highlights
Corneal cross-linking was first introduced by Wollensask et al in 2003.[1]
There was no significant difference between the two groups in terms of demographic, uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent (MRSE), topography, pachymetry, and corneal higher-order aberrations (HOAs) except for anterior trefoil values, 0.94 ± 48 μm in A-CXL group versus 0.64 ± 0.41 μm in S-CXL (P = 0.011)
The UDVA and CDVA values were significantly improved postoperatively compared with baseline in A-CXL group (P < 0.05)
Summary
Corneal cross-linking was first introduced by Wollensask et al in 2003.[1]. Zhang et al demonstrated that the term “collagen crosslinking” is misleading, as the actual cross-links, induced by interaction of ultraviolet A (UVA) and riboflavin, occurs between the amino terminals of the collagen side chains and the proteoglycans of the extracellular matrix and not between and within the collagen fibers.[2]. Bunsen-Rosoe law of reciprocity states that an increased intensity coupled with reduced exposure time theoretically delivers a total dose to the tissue equivalent to that applied in standard treatment.[6] Evaluations of the difference of the outcomes between S-CXL and A-CXL and their impact on the anterior corneal flattening, hyperopic shift, astigmatism, and corneal thinning have gained a particular importance for the refractive surgeons in choosing the CXL protocol to combine with other refractive surgery procedure.[7,8,9]. We aimed to compare the visual outcomes, topographic parameters, and corneal higher-order aberrations (HOAs) values (anterior and posterior) of an A-CXL 10 mW/cm min and the standard CXL protocol using 3 mW/cm min
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