Purpose To compare the effect, failure rate and the risks of corneal cross-linking (CXL) in keratoconus patients aged Z35 years to patients o35 years. Methods In 141 eyes of 116 keratoconus patients we compared the changes in best phoropter-corrected visual acuity (BCVA) and maximum keratometry values (K max ) before and 12 months after CLX in patients aged Z35 years (n ¼ 34, 38 eyes) to the cohort of patients below 35 years of age. Results Overall, CXL significantly improved BCVA from 0.487 logMAR (95% confidence interval (CI) 0.426-0.548) by À 0.197 logMAR (95% CI À 0.243 to À 0.150; Po0.001) and reduced K max from 48.96 diopter (Dpt) by À 1.33 Dpt (95% CI À 1.85 to À 0.81: Po0.001). Age Z35 years had no effect on the changes of BCVA ( À 0.02 (95% CI À 0.13 to 0.09); P ¼ 0.757) or K max (0.58 (95%CI À 0.51 to 1.68); P ¼ 0.294) as compared with younger patients. In 54 patients (55 eyes, 38.5%) aged o35 years and in 18 patients (18 eyes, 47.4%) aged Z35 years, BCVA increased by Z2 Snellen lines. Failure (increase in K max Z1 Dpt) was observed in 17 eyes (16.5%) of patients aged o35 years and in 3 eyes (7.9%) of patients aged Z35 years during the 12-month follow-up period. Adverse outcomes (loss of Z2 Snellen lines) occurred in 4 (3.9%) eyes of patients aged o35 years and 1 (2.6%) eye of a patient aged Z35 years. Conclusion Effects and adverse events of CXL treatment do not seem to differ between subjects younger or older than 35 years.

This study confirmed an earlier observation that there is a disparity between the change in refraction and the reduction in corneal power measured by videokeratography and with the manual keratometer. Topographical changes from PRK and the subsequent wound-healing processes are likely to falsify objective measurements. The keratometric value in the center of the cornea, since it is not measured by manual keratometry and videokeratography, may actually be lower.

The result of PARK in eyes with low to moderate degrees of myopic astigmatism was satisfactory. However, in eyes with extensive scarring and wound healing activity after the first ablation, re-treatment was less predictable.