Sir,
We thank Vinciguerra et al1 for their interest and valuable comments on our article.2 The rationale of our study was to determine the preoperative patient characteristics affecting visual and topographic outcomes of corneal collagen crosslinking (CXL) for progressive keratoconus. We found that patients with a worse preoperative corrected distance visual acuity (CDVA, ≤20/40 Snellen equivalent) tend to experience more visual improvement after CXL treatment (P<0.001).2 However, an older age (≥30 years) and a thinner cornea (thinnest pachymetry <450 μm) appear to be positive preoperative predictors for more flattening in maximum keratometry (P=0.024 and P=0.005, respectively).2 Similarly, Vinciguerra et al3 reported that age between 18 and 39 years has positive effect on the outcomes of CXL, and they found a significant association between the thinnest pachymetry and sphere change after CXL treatment.
Unlike the studies of Vinciguerra et al3 and Greenstein et al,4 our analysis showed no significant relation between initial maximum keratometry and postoperative improvement in visual acuity and maximum keratometry.2 In our study, cut points were determined as 54 diopters (D) for the maximum keratometry and 450 μm for the thinnest pachymetry in accordance with the current literature and median values. A significant result could be found by shifting cut point to 58.5 D for maximum K, whereas inappropriate and unbalanced number of subjects between subgroups did not allow using this cut point in our study.
We agree with the comments of Vinciguerra et al1 that intraoperative corneal thickness measurement is crucial and swelling riboflavin solutions should be used when the intraoperative minimum corneal thickness is <400 μm to prevent complications. However, in our study we excluded the eyes, which received swelling riboflavin solution during the CXL procedure.2
In conclusion, our results suggest that age, preoperative CDVA, and thinnest pachymetry seem to affect the outcomes of CXL treatment. Moreover, Vinciguerra et al and several studies concluded that preoperative maximum keratometry has an effect on the clinical improvement after CXL treatment.3, 4, 5, 6 However, the predictive threshold values for each preoperative factor remain to be investigated.
References
Vinciguerra P, Romano V, Romano MR, Azzolini C, Vinciguerra R . Comment on, ‘Factors affecting outcomes of corneal collagen crosslinking treatment’. Eye (Lond) 2014; 28 (8): 1032–1033.
Toprak I, Yaylalı V, Yildirim C . Factors affecting outcomes of corneal collagen crosslinking treatment. Eye (Lond) 2014; 28 (1): 41–46.
Vinciguerra R, Romano MR, Camesasca FI, Azzolini C, Trazza S, Morenghi E et al. Corneal cross-linking as a treatment for keratoconus: four-year morphologic and clinical outcomes with respect to patient age. Ophthalmology 2013; 120 (5): 908–916.
Greenstein SA, Hersh PS . Characteristics influencing outcomes of corneal collagen crosslinking for keratoconus and ectasia: implications for patient selection. J Cataract Refract Surg 2013; 39 (8): 1133–1140.
Koller T, Pajic B, Vinciguerra P, Seiler T . Flattening of the cornea after collagen cross-linking for keratoconus. J Cataract Refract Surg 2011; 37: 1488–1492.
Yam JC, Cheng AC . Prognostic factors for visual outcomes after crosslinking for keratoconus and post-LASIK ectasia. Eur J Ophthalmol 2013; 23 (6): 799–806.
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Toprak, I., Yaylalı, V. & Yildirim, C. Response to Vinciguerra et al. Eye 28, 1033–1034 (2014). https://doi.org/10.1038/eye.2014.91
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DOI: https://doi.org/10.1038/eye.2014.91