Further investigations on the crosslinking of tarsal collagen as a treatment for eyelid laxity: Optimizing the procedure in animal tissue

Purpose : A follow-up experimental study on the exposure of animal tarsal plate to ultraviolet-A radiation aimed at establishing an optimum range for safe irradiation conditions. Methods : Sheep tarsus specimens were excised post-mortem and then subjected to irradiation with ultraviolet-A rays (wavelength 365 nm) at higher irradiances than those reported in an initial study, using a laboratory radiation source. The mechanical properties (tensile strength and Young’s modulus) of irradiated and non-irradiated samples were evaluated in a mechanical tester. The test and control specimens were examined histologically with an aim to assess the effects of radiation upon the meibomian glands and tarsal collagen networks, and to establish a safe range for the exposure irradiance level. Results : As expected, irradiation induced both stiffening and strengthening of the tarsal plate specimens. At an irradiance of 50 mW/cm 2 for 3-min exposure, these effects were at their maximum level, after which a decline in mechanical characteristics were observed. No destruction of the tarsal connective tissue or the meibomian glands were noticed up to an irradiance of 125 mW/cm 2 for 3-min exposure, corresponding to a fluence of 22.5 J/cm 2 . Histology revealed that the collagen network surrounding the glands were packed more compactly following irradiation. At a fluence of 45 J/cm 2 , massive destruction of periglandular collagen-rich network and meibocytes were demonstrated histologically. Conclusions : The study indicates that irradiation of tarsal collagen leading to tissue stiffening shall be carried out at levels of fluence between 10 and 15 J/cm 2 , a region that is deemed safe. The exposure time can be adjusted according to the surgeon’s decision.