Table 1: Studies on Effectiveness of collagen crosslinking procedure.

Author	Study Design	Follow-Up Period	Results
Wittig-Silva et al., [14]	Randomized Controlled trial	12-month	Collagen crosslinking procedure was effective against progression of keratoconus.
Hersh et al., [15]	Complex study design	12-month	1.5 D reduction in average keratometry and 2 D decline was observed in maximum keratometry among the patients treated for keratoconus.
O’Brart et al., [16]	Randomized prospective study	18-months followup period	Utilization of the collagen crosslinking procedure assists in the mitigating keratoconus progression.
Spoerl et al., [21]	Review Paper	-	Results highlights the use of the safety protocols which include riboflavin application for half an hour before exposure to ultraviolet radiations, removal of epithelium, ultraviolet irradiance of 370 nm wavelength, and 400 μm minimum corneal thickness. The adequate technique and safety procedure must be followed as it can lead to damage of retina, lens, and endothelium.
Baiocchi et al., [29]	Randomized retrospective study	-	Epithelium removal helps in the effective and safe concentration of riboflavin.
Wachler et al., [30]	Review Paper	-	Concentration of critical micelle and tetracaine lowers the retreatment rate.
Stojanovic et al., [26]	Non-randomized retrospective study	12-month followup period	Transepithelial technique was effective in decreasing Kmax, cylindrical equivalent, SE, and enhanced CDVA without any considerable harmful effects.
Raiskup et al., [32]	Experimental analysis		Regardless of the concentration of alcohol content in blood, similar riboflavin absorption level is observed through the cornea epithelium.
Kocak et al., [33]	Retrospective study	12-months followup period	Epithelium-off technique was effective in declining keratoconus progression.
Choi et al., [42]	Quantitative study		Corneal thickness improved by 107% post CXL administration in ex vivo models.