Ex vivo thermographic analysis of the eyelid conjunctival surface during ultraviolet A-mediated photochemical crosslinking of tarsal collagen: A step in translational safety evaluation

Ultraviolet A (UVA)-induced collagen crosslinking can mechanically reinforce collagenous tissues and is being translated as a minimally invasive treatment for pathological eyelid laxity, yet the extent of irradiation-related heating at the conjunctival–tarsal interface remains unclear. In this study, we developed a novel procedure to treat pathological eyelid laxity. The methodology is based on the photocrosslinking of tarsal collagen, leading to mechanical reinforcement of the entire eyelid. In our previous studies, exposure to ultraviolet A (UVA) radiation at fluences below 20 J/cm2 did not cause histopathological alterations to the eyelid tissues. Here, we further evaluated biological safety by quantifying conjunctival surface temperature increases during UVA irradiation to inform clinical translation. Using ex vivo sheep eyelids as a model, we used infrared thermography to measure the temperatures attained on the tarsal conjunctival surface during UVA irradiation (365 nm) at four irradiances for a maximum exposure time of 3 min, corresponding to fluences of 8.1, 13.5, 27, and 45 J/cm2. Both the exposure time and irradiance caused an asymptotic increase in temperature, while a linear dependence was observed between fluence and temperature increase (ΔT). The recorded values for ΔT ranged from 3.3°C to 14.0°C. In summary, at clinically practicable fluences (