Photochemical Collagen Cross-Linking Reverses Elastase-Induced Mechanical Degradation of Upper Eyelid Tarsus.

INTRODUCTION: The floppy eyelid syndrome describes an eyelid disorder characterized by floppy tarsal plates that may be caused by a loss of elastin. The authors attempted to create floppy eyelids by digesting elastin from cadaveric tarsus and then treated them with cross-linking using ultraviolet A and riboflavin. METHODS: Nine right and 9 left upper eyelids were excised from cadavers. Four vertical strips of central tarsus were removed from each eyelid. One strip of tarsus from each eyelid was treated with 10 units/ml of elastase for 2 hours. Another tarsal strip from each eyelid was immersed in normal saline for 2 hours (control). A third strip from the same eyelid was cross-linked using ultraviolet A at 6 mW/cm for 18 minutes. Finally, a fourth strip of tarsus was cross-linked in the same manner following treatment with elastase for 2 hours. A microtensile load cell was used to measure the Young modulus (stiffness) of each tissue. RESULTS: Mean (standard deviation) Young modulus for controls (18.9 +/- 3.6 MPa) was significantly higher than samples treated with elastase alone (6.6 +/- 3.8 MPa, p <0.01). Samples that were treated with cross-linking after elastase had a mean (standard deviation) Young modulus of 26 +/- 2.3 MPa, while those treated with cross-linking alone had a mean (standard deviation) Young modulus of 34 +/- 0.15 MPa. The differences in stiffness between all groups were significant (p <0.01). DISCUSSION: Treatment with elastase significantly reduces the stiffness of tarsal plates. This effect is reversed by cross-linking, raising the possibility of using this modality for the treatment of FES.