In Vitro Effect of the Biomechanics After Photodynamic Therapy (PDT) Intervention on Rabbit Cornea

Objective: To observe the change of the biomechanical properties of rabbit cornea after the intervention by corneal collagen cross linking (CXL) and toluidine blue O combined with red light (TBOR).Methods: The study was carried out in compliance with the ARRIVE guidelines. 20 healthy adult New Zealand white rabbits were randomly divided into two groups. One group was taken with Riboflavin combined with UV light therapy in the right eye of healthy New Zealand white rabbits, and the other group was taken toluidine blue O combined with red light (TBOR) treatment. All left eyes were taken as controls. Parameters, from Pentacam and Corvis ST like K1 (The keratometry readings of the flattest), K2 (The keratometry readings of the steepest), ACD (Anterior chamber depth), Pupil diameter, ACA (Mean angle of the anterior chamber), ACV (Volume of the anterior chamber), bIOP (Biomechanical Intraocular pressure), CT (Corneal thickness, pachymetry), A1 Time(Time from starting until the first applanation), A1 Velocity(Corneal speed during the first applanation moment), A2 Time (Time from starting until the second applanation), A2 Velocity (Corneal speed during the second applanation moment), HC Time(Time from starting until highest concavity is reached), Peak Dist(Distance of the two “peaks” at highest concavity) and HC-Radius(The radius at highest concavity), were examined before and 2 weeks after intervention. The rabbits were sacrificed after anesthesia. Then, their corneas were removed for corneal stretch test.Results: With the examination of Pentacam and Corvis ST, IOP(11.28 ± 11.2mmHg v.s. 6.66 ± 4.02mmHg) and A1 time(7.03 ± 1.27s v.s. 6.55 ± 0.35s) were increased, comparing with those before intervention. From the in vitro corneal stretch test, the tangent modulus of the CXL group was more than 3 times of the Control group, whereas the tangent modulus of the TBOR group was about 0.7 times to that of the Control group.Conclusions: From the rabbit cornea intervention with CXL and TBOR, CXL showed an obvious effect of increasing the hardness of rabbit cornea, while TBOR may did no help to increase the hardness of cornea.