Abstract
Keratoconus is a corneal disorder in which the cornea becomes cone-shaped due to stromal thinning and corneal weakening. It mainly affects young individuals and although the prevalence is low (1:2000), the impact on quality of life is high. Despite much effort, still no cure has been found for keratoconus.
Although it
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does not cure keratoconus, CXL can be considered a revolutionary contribution, since it is the only treatment option for progressive cases. CXL is a relatively low invasive procedure to increase corneal rigidity. The treatment is performed a follows: after epithelial removal, isotonic riboflavin drops are applied to the cornea for 30 minutes and subsequently ultraviolet-A irradiation starts for 30 minutes. Reasons to remove the epithelium are that it acts a barrier for riboflavin molecules to enter the stroma, in addition to the fact that epithelium absorbs UV light. Due to the removal of epithelium, patients sensate (sometimes intensive) pain during the first postoperative hours, which extinguishes in the next day(s). Other known symptoms are blurry vision and photofobia. Complete healing of the corneal epithelium is generally within 5 days, and the risk of early post-operative complications (3-8%) is mostly related to epithelial healing. Transepithelial CXL whereby the epithelium is left intact might avoid epithelial healing problems and would be a less painful procedure.
In general, standard (epithelium-off) CXL has been shown to be an effective treatment with a high success rate (92%) of halting keratoconus progression. In our randomized controlled trial, transepithelial CXL performed significantly less than standard epithelium-off CXL. In 23% of eyes that underwent transepithelial CXL, keratoconus progression continued after 1 year. Progression was halted in 100% in the group with standard epithelium-off CXL. Therefore, we do not recommend replacing the standard CXL treatment for transepithelial CXL.
We also analyzed the epithelium-off CXL effect in patients at the pediatric age (<18 years). In young patients, keratoconus progression can be rapid and intervention with CXL has been advised as soon as any clinical sign of progression is noted. For the last years, there is a trend to perform CXL in patients < 18 years directly after the diagnosis is made, instead of waiting for signs of progression (as is the case in adults ≥ 18 years). This is important, since visual acuity is often still very good at this point and although risks of post-operative complications are low, a clear communication with parents and more than average patient care is mandatory when treating young patients. In our study, we found an equally safe result in pediatric patients compared to patients from 18-26 and >26 years old. Furthermore, pediatric patients showed more visual improvement compared to the other groups. An uncertainty in pediatric patients is the duration of the CXL effect. The turnover rate of stromal collagen ranges between 2 and 7 years. Since the renewed collagen might not have the same biomechanical strengthening as the previous crosslinked collagen, young patients might need repeated CXL treatments.
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