Corneal crosslinking (CXL) is a wonderful treatment intervention for patients with keratoconus and other ectasias—but it still exposes the eye to ultraviolet A (UVA) radiation. The Dresden protocol, for example, subjects the corneal endothelium to about 0.32J/cm2 of radiation, while the retina receives approximately 0.22 J/cm2 of radiation during CXL.

A team of investigators recently discovered that this amount of exposure avoids damage to the retinal structures, considering the accepted damage threshold for the retina sits at 7.7 J/cm2.  Using mfERG, researchers from Germany found that P1 amplitude density (P1-AD) values—suggesting functional disturbance of the cone receptors—dropped after CXL but returned to preoperative (physiologic) values six weeks later.

This prospective, single-center cohort study evaluated 17 eyes of 17 patients who underwent CXL with the standard Dresden protocol for the treatment of corneal ectasia. The team documented the P1-AD, visual acuity, corneal densitometry and macular thickness (MT) preoperatively and at two and six weeks postoperatively.

The investigators found the P1-AD response decreased significantly two weeks after CXL but normalized by the six-week follow up. The researchers noted corneal haze, not photoreceptor dysfunction, might be the cause of decreased P1-AD response, considering the location of the temporary decrease.

The study also recorded a statistically significant decrease in the parafoveal and perifoveal macular thickness at the two-week mark, which persisted at the six-week visit. This led the researchers to speculate that phototoxical damage of the retina cannot be excluded; however, no research explores the effect of corneal haze on retinal thickness measures, they noted in their paper.

“Although temporary retinal dysfunction during the first postoperative weeks cannot be totally excluded, the return of six-week P1-AD to preoperative levels confirms the safety standards of the duration and intensity of UVA radiation as proposed by the Dresden protocol,” the study authors concluded.

Lazaridis A, Tsamassiotis S, Konstantinos Droutsas K, et al. Revisiting the safety of the corneal collagen crosslinking procedure: evaluation of the effect of ultraviolet a radiation on retinal function and structure. Cornea. September 30, 2019. [Epub ahead of print].