Theoretical Basis, Laboratory Evidence, and Clinical Research of Chemical Surgery of the Cornea: Cross-Linking

Table 1

In vitro and in vivo evidences of corneal cross-linking protocols.

Protocol	In vitro	In vivo
Epi-off CXL (Dresden Protocol)	Increased Young’s modulus [20, 21], resistance to enzymatic degradation [22], and collagen fiber diameter [23]	Improvement in VA, K reading, refraction, and halt of ectasia progression
Epi-on CXL	Riboflavin penetration requires more time than with epi-off techniques; Epithelium permeabilization can be achieved with molecules as cyclodextrins [24] and benzalkonium chloride in association with NaCl [25]	Improvement in VA and topographic findings; Halt of ectasia progression; There is a lot of controversy about results of this technique [26]
Ultrafast CXL	Young’s modulus similar to traditional CXL [27]	Equivalent in VA, refraction and pentacam parameters [28, 29], and OCT imaging [29]
Athens protocol	No data available	Superiorly with a better BSCVA, mean K reduction, spherical equivalent, and corneal haza score [30]