Localised corneal haze and scarring following pulsed accelerated collagen cross-linking for keratoconus

Corneal collagen cross-linking (CXL) is the only treatment that delays or arrests progression of keratoconus. CXL is a safe procedure with few complications. CXL protocols vary depending on time and energy used but all are safe and effective. Variations from the original Dresden protocol are based on the Bunsen-Roscoe law (BRL) [1], which states that “a certain biological effect is directly proportional to the total energy dose irrespective of the administered regime”. [2] This implies that higher energy applied over short duration will have the same biological effect as lower energy applied over longer duration [1].Forty-nine patients with progressive keratoconus had (epithelium-off) accelerated CXL with the Avedro KXL® system. All patients had 10 min of 0.1% riboflavin soak (1 drop every 2 min). Twenty-one patients had CXL with 8-minute pulsed protocol (1 sec on/1 sec off) with irradiation of 30 mW/cm2 (group 1). Twenty-eight patients had 12-minute continuous irradiation with 10 mW/cm2 (group 2). Both groups had total energy of 7.20 J/cm2.We compared complications between the 2 groups and analysed these to pre-operative parameters (age, sex, maximum K, K1, K2, mean keratometry, corneal pachymetry at the thinnest location, cylinder and spherical equivalent) to determine any statistically significant correlation. Four patients from group 1 developed localised haze of which 2 were associated with an epithelial defect (Fig. 1). All four had persistent residual scar which led to initial drop of best corrected visual acuity (BCVA) but returned to baseline at six months. There was no statistically significant difference between pre-operative parameters of these patients and the rest of patients in the group. Similarly, there was no statistically significant difference in pre-operative parameters between groups 1 and 2 (Table 1). The depth of the demarcation line also did not show a difference in the two groups