Revisiting the Safety of the Corneal Collagen Crosslinking Procedure: Evaluation of the Effect of Ultraviolet A Radiation on Retinal Function and Structure.

Purpose: To evaluate the effect of ultraviolet A radiation on retinal function and structure after the corneal collagen crosslinking procedure. Methods: In the present prospective, single-center cohort study 17 eyes of 17 patients who underwent collagen crosslinking (Dresden protocol) for the treatment of corneal ectasia were examined preoperatively and at 2 and 6 weeks postoperatively with multifocal electroretinogram and optical coherence tomography. The P1 amplitude density (P1-AD) of the central retinal response was documented in 5 concentric rings, with ring 1 (R1) representing the foveal response and rings 2 to 5 (R2-R5) corresponding to successive annuli of stimulation. Visual acuity, corneal densitometry at the 0 to 2 mm zone and at the 2 to 6 mm annulus, and macular thickness (MT; central, 1 mm, 3 mm, and 5 mm zones) were recorded. Results: The preoperative values of P1-AD were R1 = 109.96 +/- 28.96, R2 = 49.8 +/- 14.46, R3 = 29.85 +/- 8.9, R4 = 19.33 +/- 6.3, and R5 = 16.39 +/- 5.48 nV/deg(2). At 2 weeks, these values were R1 = 77.54 +/- 24.47, R2 = 36.55 +/- 12.53, R3 = 21.53 +/- 7.71, R4 = 15.3 +/- 6.13, and R5 = 13.32 +/- 5.48, showing a significant reduction for R1-R4 (P <= 0.026). The 6-week P1-AD was R1 = 99.8 +/- 31.23, R2 = 40.67 +/- 16.39, R3 = 24.98 +/- 7.13, R4 = 16.35 +/- 4.84, and R5 = 13.76 +/- 3.98, showing no significant differences compared with preoperative values (P >= 0.054). Corneal densitometry increased significantly at 2 weeks (P < 0.001) and remained increased at 6 weeks (P < 0.001), showing statistically insignificant correlations with 2-week P1-AD (P >= 0.553). The central MT increased (P = 0.787), whereas MT at 1 mm (P = 0.444), 3 mm (P = 0.039), and 5 mm (P < 0.001) zones decreased. Conclusions: The return of P1-AD to preoperative (physiologic) values at 6 weeks confirms the safety standards of the duration and intensity of ultraviolet A radiation, as proposed by the Dresden protocol. However, temporary postoperative retinal dysfunction cannot be excluded.