Table 4. Summary of keratometric outcomes (Kmax flattening, stabilization rate) from representative studies on transepithelial cross-linking protocols in progressive keratoconus.

D: diopter; Epi-off: epithelium-off protocols (conventional Dresden method); Epioxa™: FDA-approved epi-on CXL using oxygen-enriched RF for keratoconus; EpiSmart: investigational epi-on CXL with RiboStat (RF + sodium iodide); I-CXL: transepithelial corneal collagen crosslinking using iontophoresis (riboflavin delivery via iontophoresis); Kmax: maximum keratometry; NR: not reported; NS: not significant (p-value > 0.05); RF: riboflavin; TE-CXL: transepithelial corneal cross-linking; TPGS: tocopheryl polyethylene glycol succinate (water-soluble form of vitamin e)

Study	TE-CXL Protocol	Kmax Change	Comparison	Timepoint	Stabilization Rate
Al Fayez et al., 2015 [37]	Standard TE-CXL	+1.1 D  (p < 0.05)	vs Dresden: -2.4 D (p < 0.0001)	3 years	41% vs 100%
Bikbova et al., 2016 [40]	I-CXL	-0.9 D (p < 0.05)	vs Dresden: -1.8 D (p < 0.05)	2 years	100% vs 100%
Caruso et al., 2016 [41]	Vitamin E-TPGS	-1.01 ± 1.22 D  (p < 0.001)	NR	2 years	80%
Vinciguerra et al., 2016 [61]	I-CXL	-0.31 ± 1.87 D  (NS)	vs Dresden: -1.05 D (p < 0.01)	1 year	NR
Stulting et al., 2018 [59]	Enhanced RF	-0.48 D (p < 0.001)	NR	2 years	100%
Epstein et al., 2022 [45]	EpiSmart	-0.76 D (p < 0.001)	NR	1 year	75%
Smith et al., 2025 [57]	Epioxa™ + O2	≤ -1.0 D (p < 0.05)	vs sham: increased  (p < 0.0001)	1 year	NR