Corneal Haze and Densitometry in Keratoconus after Collagen Cross-Linking by Three Different Protocols

PURPOSE: To evaluate postoperative corneal haze and corneal densitometry following three different corneal cross-linking (CXL) protocols; standard, accelerated, and trans-epithelial (TE). METHODS: The study recruited 104 eyes (53 patients) with progressive keratoconus divided into three groups: Group I were subjected to standard CXL, Group II to TE-CXL, and Group III to accelerated CXL (A-CXL) (10 mW/cm(2) for 9 min). Subjective and objective corneal haze measures were evaluated before and 3, 6, and 12 months post-CXL using slit-lamp biomicroscopy and Pentacam Sheimpflug camera. RESULTS: There was a significant difference in corneal densitometry between the three groups at 3 and 6 months post-CXL (P < 0.0001). By the 12(th) month, a significant statistical difference was observed only in zones (0–2 mm) and (2–6 mm) in both the anterior and the central layers. In Group I, the densitometry value of the preoperative anterior stromal layer (anterior 120 μm) was 19.42 ± 1.81. Then, it peaked at 23.12 ± 1.21 at 3 months (P < 0.0001), reached 19.82 ± 1.19 at 6 months (P = 0.007), and decreased to 19.33 ± 3.23 (P > 0.05) at 12 months. In Group II, the preoperative densitometry value of the anterior layer was 19.41 ± 1.21, peaked at 19.72 ± 1.12 at 3 months (P = 0.02), reached 19.04 ± 1.18 at 6 months (P = 0.052), and increased to 19.13 ± 1.37 at 12 months (P = 0.84). In Group III, the preoperative densitometry value of the anterior stromal layer was 19.53 ± 2.23. Then, it peaked at 24.80 ± 1.08 at 3 months (P < 0.0001), decreased to 21.75 ± 1.11 at 6 months (P < 0.0001), and reached 19.77 ± 2.26 at 12 months (P = 0.047). There was no significant correlation between the visual acuity changes and the total corneal densitometry. CONCLUSION: The TE-CXL group showed a better and earlier recovery from the haze, while the A-CXL group showed a delay in recovering and persistent increased corneal densitometry, mainly in the anterior 120 μ.