Pulse-induced Trabecular Meshwork (TM) Movement in Humans: Characterization by Phase-sensitive OCT (PhS-OCT)

Abstract

 

Purpose

 

Aqueous flows from Schlemm's canal (SC) to the aqueous veins by cyclic pulsatile mechanisms that depend on TM movement. TM movement is dependent on biomechanical properties that become abnormal in glaucoma. We hypothesized that PhS-OCT could detect and measure pulse-induced TM movement in human subjects.

 

Methods

 

10 subjects, 20 eyes; sex F/M, 6/4; mean age ±SD, 37±12; heart rate ±SD 70 ±11. A PhS-OCT system measured TM movement with a sensitivity to tissue motion at the nanometer (nm) scale. A digital pulsimeter signal was synchronized with the PhS-OCT data acquisition system through triggers. Analysis involved correlation of timing and phase lag of the digital pulse and the TM tissue wave, TM velocity measurements, relationships of TM motion to heart rate and age, strength mapping of the TM velocity wave, correlation of harmonics of the 1st 9 pulse-induced motion waves and correlation between digital and CRA pulse waves.

 

Results

 

Digital pulse peaks and TM pulse wave minima were highly correlated R2 =0.998, P< 0.0001. Frequency components of the harmonic waves were also highly correlated. (R^2=0.996, P<0.0001). Energy of TM motion was contained primarily in the 1st 4 harmonic waves (80%). The tissue phase lag was negatively correlated with heart rate (P <0.05), but not age. Velocity of maximal TM motion toward and away from SC was ~ 3µ/sec. The digital and CRA pulse were almost in phase (0.08 sec. delay).

 

Conclusions

 

PhS-OCT imaging detected and measured TM movement that was highly correlated with the cardiac pulse. TM motion strength, harmonics and velocity were characterized. PhS-OCT may provide a sensitive clinical tool for monitoring development and progression of aqueous outflow system biomechanical changes leading to pressure elevation in glaucoma.

 

 

Spatial characterization of TM motion. (A) Normalized strength mapping of the ocular tissue motion around the corneo-scleral limbus; (B) isolated TM strength mapping superimposed on the corresponding structural cross-section, enlarged view of the area marked by the dashed red square in (B). (C) and (D) isolated TM velocity cross-sections superimposed on the structural cross-section, respectively corresponding to the downward velocity toward the AC and the upward velocity toward SC external wall. (E) Linear correlation between the TM pulse peak (f-time ) and the digital pulse peak (p-time) in seconds (s) from time 0.

 

Keywords: 633 outflow: trabecular meshwork • 568 intraocular pressure • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)