Pachymetry-based Accelerated Crosslinking: The “M Nomogram” for Standardized Treatment of All-thickness Progressive Ectatic Corneas

Abstract

Purpose: To assess the safety and efficacy of a new customi­ zed epithelium­off 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/ cm 2 CXL, 20 eyes treated with 30 mW/cm 2 ACXL with conti­ nuous (10 eyes) and pulsed (10 eyes) UV­A exposure (1 sec on, 1 sec off), 20 eyes treated with 15 mW/cm 2 pulsed light ACXL and 20 eyes using the 9 mW/cm 2 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 cross­linking profile was determined according to a calculated depth of the demarcation line and the threshold cross­link concentration adopting the conventional 3 mW/cm 2 protocol as a benchmark. Results: The average demarcation depths were 350 ± 50 µm for the 3 mW/cm 2 conventional protocol, 200 ± 50 µm for the 30 mW/cm 2 continuous light ACXL, 250 ± 50 µm for the 30 mW/ cm 2 pulsed light ACXL and 280 ± 30 µm for the 15 mW/cm 2 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 R 2 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.