Microscope Real-time Video (MRTV), High- resolution OCT (HR-OCT) & Histopathology (HP) to Assess How Transcleral Micropulse Laser (TML) Affects the Sclera, Ciliary Body (CB), Muscle (CM), Secretory Epithelium (CBSE), Suprachoroidal Space (SCS) & Aqueous Outflow System

Abstract

Purpose : Mechanisms of IOP reduction after TML remain unclear although TML is widely used in the management of glaucoma. We describe 3 imaging modalities to explore tissue changes induced by TML that may assist in understanding mechanisms of action & improving treatment parameters.

Methods : Immediately after removal of non-human primate eyes, radial sections of the limbus (2 mm wide) were maintained in a saline bath & a micropulse laser probe positioned so the beam path passed through sclera to CB. To simulate clinically relevant energies, Joules used in sections were 0.75 (n=2), 1.50 (n=2), & 2.5 (n=1). MRTV imaged throughout the pulse, HR-OCT before & after; HP followed after. Distance from scleral spur (SS) to probe before & after the laser was measured with ImageJ using MRTV images; paired t-tests were done with JMP.

Results : The MRTV beam path tracing focused in tissue at ~700 μm depth near the interface of sclera & longitudinal CM. MRTV showed that the internal scleral surface facing the CB in the path of the beam immediately underwent shrinkage. The adjacent CB longitudinal muscle also simultaneously shortened or contracted. Sclera & CM shrinkage resulted in local SCS enlargement. The scleral spur moved posteriorly by 27.0 ± 3.0, 107.6 ± 8.6 & 92.4 ± 12.3 μm at 0.75, 1.5 & 2.25 Joules respectively; final position in each differed significantly from baseline (p < 0.0001). The attached TM moved inward & posteriorly with Schlemm’s canal (SC) enlargement. Histology & a newly developed platform for imaging the entire CB thickness with OCT confirmed the RTV findings. No CB secretory epithelium damage was identified with MRTV, HR-OCT or HP.

Conclusions : The TML caused a Δ in sclera thickness, shortening & local shrinkage of the longitudinal CM with enlargement of the SCS. Inward & posterior movement of the SS & TM caused SC to enlarge. Absence of CBSE damage suggest SCS enlargement, a uveoscleral flow increase & conventional aqueous outflow pathway changes as mechanisms of action, rather than direct CBSE damage. Additional lab studies may assist in further characterizing mechanisms of action & provide insights related to appropriate treatment parameters.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Microscope Imaging from Real Time Video

 

High Resolution OCT & Histology Imaging