Purpose: To assess the safety and efficacy of a new customized epithelium-off accelerated crosslinking (ACXL) nomogram “M nomogram” based on preoperative corneal optical thinnest point for progressive keratoconus and iatrogenic corneal ectasia.
Methods: Comparative analysis including the measured depths of the demarcation lines by in vivo confocal microscopy (IVCM) and corneal OCT in 20 eyes treated with conventional 3 mW/cm2 CXL, 20 eyes treated with 30 mW/cm2 ACXL with continuous (10 eyes) and pulsed (10 eyes) UV-A exposure (1 sec on, 1 sec off), 20 eyes treated with 15 mW/cm2 pulsed light ACXL and 20 eyes using the 9 mW/cm2 ACXL protocol. IVCM was performed by the HRT II Rostock Cornea Module (Heidelberg, Germany) and corneal OCT by the OptoVue (Freemont, Irvine, USA). The mathematical cross-linking profile was determined according to a calculated depth of the demarcation line and the threshold cross-link concentration adopting the conventional 3 mW/cm2 protocol as a benchmark.
Results: The average demarcation depths were 350 ± 50 μm for the 3 mW/cm2 conventional protocol, 200 ± 50 μm for the 30 mW/cm2 continuous light ACXL, 250 ± 50 μm for the 30 mW/cm2 pulsed light ACXL and 280 ± 30 μm for the 15 mW/cm2 pulsed light ACXL. There was a very high correlation between the depth of the demarcation line between the measured and calculated data with a slope of m = 1.03 and an R2 value 0.73.
Conclusion: ACXL M nomogram allows safe and efficacious CXL parameters setting based on preoperative minimum corneal thickness also including a more standardized treatment of thin ectatic corneas between 250 μm and 400 μm.