Estimation of corneal thickness ex vivo and in vivo at instillation of photosensitizer solutions in different modifications of UV corneal crosslinking

Abstract

Objectives: to evaluate the effectiveness of photosensitizer solutions in the experiment in different modifications of standard UV corneal crosslinking. Materials and Methods. Experiments were performed on 32 enucleated porcine eyes ex vivo and 12 rabbits (24 eyes) in vivo, divided into 4 groups depending on instillations of the photosensitizer solutions: Dextralink, Ribolink, Hypolink and Riboflavin. Evaluation of corneal saturation was performed using two modifications of standard UV CXL: in the first case, instillation of the photosensitizer solution was performed during the entire crosslinking procedure (30 min - saturation and 30 min - ultraviolet irradiation); in the second case, instillations lasted only for the first 30 minutes, the precorneal riboflavin film was removed, and instillation of solution was not performed. Results and Discussion. Instillation of photosensitizer solutions within 60 minutes showed that Dextralink significantly reduced the thickness of the cornea by about 24 % ex vivo and 21 % in vivo, while Hypolink, on the contrary, caused its increase by 9 % ex vivo and 23 % in vivo, respectively. The use of Ribolink and Riboflavin did not change the linear parameters of the cornea during the entire follow-up period. The results of the 2nd series of studies showed that effects of solutions on the cornea during their instillation for 30 minutes were generally preserved during the entire observation period up to 60 minutes. In the group where Dextralink and Hypolink solutions were used, there was a slight tendency to normalization of the initial parameters of the cornea. Conclusion. Safe and effective implementation of UV crosslinking of the cornea is possible on the basis of a rational approach to the performing the stages of stroma saturation with photosensitizer solutions, depending on the initial state of the cornea: Dextralink is recommended for a thickness of more than 450 m, Ribolink - at 400-450 m, Hypolink - from 350 to 400 m. Halting of instillations on the saturated stroma during UV irradiation is advisable to be accompanied by intraoperative control of its thickness. When performing a standard crosslinking technique, where instillations of photosensitizer accompany the stage of UV irradiation of the cornea, it is necessary to take into account the presence of a precorneal film that can absorb some of the radiation energy. The peculiarity of this crosslinking technique can be considered as a potential way to protect intraocular tissues from excessive exposure to UV radiation.

Keywords

• corneal crosslinking
• riboflavin
• keratoconus
• cornea
• corneal thickness