Stiffening of rabbit sclera by bacteriochlorophyll derivative WST11 and near infrared illumination (NIR)through the cornea

Abstract

Purpose : Sclera stiffening in rabbits induced by external impregnation of WST11 and NIR illumination through the cornea; Atomic force microscopy (AFM) and biomechanical study

Methods : Seventeen pairs of rabbit eyes were enucleated post mortem. One eye of each pair was randomly chosen for treatment. The pupil was dilated with tropicamide 1% drops and the episcleral tissue was removed. The sclera was impregnated with 2.5 mg/ml of WST 11 in saline for 20 minutes.Afterwards the sclera was illuminated through the cornea at 755nm (NIR) using a 3 mirror Goldman lens for 10 minutes. The incident light was measured to be 10 mW/cm².After the treatment, the eye was dissected and the retina and choroid were removed. Thirteen pairs were assigned for biomechanical stretching and 4 pairs for AFM measurements (using JPK Nanowizard 3). Circumferential scleral strips 4 mm wide were cut from the treatment area. A similar control strip was prepared from the contralateral eye at the same position. Sclera thickness was measured by mechanical micrometer caliper. Stress-strain measurements were performed by a biomechanical tester (Minimat, Germany). Strips for AFM were washed with 2% Triton X-100 followed by several rinses with PBS and were cut in two halves, for measuring the internal and external side of the sclera. Young's modulus, was determined at the sub-micron scale by AFM indentation curves using pyramidal silicon probes, and analyzed using a Hertzian model

Results : Biomechanical measurements demonstrated an increase of 86.37 % in the maximal stress, from 7.12 Megapascal (MPa) to 13.27 MPa (p≤0.01) after treatment. Furthermore, Young’s modulus increased by 64.38 %, from 33.72 Megapascal to 55.43 MPa (p≤0.001) after treatment. AFM measurements showed that the average Young's modulus after treatment of the internal and external sides of the sclera were 1.7 (p≤0.1726) and 3.82(p≤ 0.007) times greater respectively than untreated controls.

Conclusions : This novel treatment with WST11 and NIR illumination trhough the pupila induced scleral stiffening in ex-vivo eyes. This minimally invasive treatment may be suitable to halt the progression of degenerative myopia.In-vivo studies are needed to demonstrate the safety and long-term efficacy in inhibiting axial length elongation

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.