Pulse-dependent Trabecular Meshwork Motion: Direct Microscope Observation and Measurement in Radial Limbal Segments of Non-human Primate Eyes

Abstract

 

Purpose

 

To describe a microscopic technique to observe, video & measure large pulse-dependent trabecular meshwork (TM) excursions into Schlemm’s canal (SC) and associated recoil that occur on a time scale of milliseconds.

 

Methods

 

Measurement of pulse-induced TM motion in radial segments in ex vivo macaca nemestrina eyes (5), radial 350 um limbal segments (10), cornea and sclera of segments pinned into paraffin in Petrie dish, ciliary body tensioned under direct visualization to optimize SC dilation, then pinned; 45-power microscope. Syringe attached to 27 gauge cannula (ID 200 um), 18 mpixel camera, videography (30 fps), micrometer. FIJI image analysis program for measurement of Schlemm’s canal anterior-posterior (AP) length, SC height (SCH), SC area (SCA) & length of apposition between SC inner and SC external wall (SCAP). Time intervals were from baseline until no further TM distention or recoil could be detected.

 

Results

 

Videography demonstrated easily visible pulse-dependent TM movement in response to pulse waves in each of the radial segments. Analysis of a pulse wave (Fig. 1 & 2) involved TM movement duration of 167 msec.; SCH decreased from 85 to 16 um, (TM velocity 390 um/sec); SCA decreased from 12,823 to 452 um ²; SCAP increased from 0 to 166 um progressing from anterior to posterior along SC length, reducing linear area of open SC from 226 to a 44 um region at a V-shaped area of a collector channel ostia at the posterior end of SC. In another segment, TM elasticity was assessed by measuring SCH to determine distension and recoil in 5 infusion cycles. Distention duration mean 586±219 msec. Velocity 23.4±12.5 msec. Recoil duration mean 526±132 msec. Velocity 17±6.4 msec.

 

Conclusions

 

The microscope technique permits direct observation, videography and measurement of TM motion. Observable and measureable characteristics of TM movement include distention and recoil involving SCH, SCA, SCAP and velocities. The TM appears to be markedly compliant with elastic properties making it capable of undergoing rapid large excursions into SC in response to IOP transients. Such excursions may induce rapid SC volume changes in vivo.

 

 

Fig. 1 Trabecular meshwork and Schlemm's canal appearance before an after an infusion pulse wave.

 

 

Fig. 2 Measurements from images in Fig. 1

 

Keywords: 735 trabecular meshwork • 633 outflow: trabecular meshwork • 568 intraocular pressure