Non-Invasive Assessment of Aqueous Outflow in Collector Channels by Spectral Domain Optical Coherence Tomography (SD-OCT)

Abstract

 

Purpose:

 

To compare collector channel (CC) flow with Schlemm’s Canal (SC) morphology.

 

Methods:

 

SC ostia and CC’s distal to the ostia were imaged with a modified Bioptigen (Bioptigen Inc, USA; SuperLum LTD., Ireland) SD-OCT in cross-section in both eyes of 14 healthy subjects. Ten frame raster scans (700 1.3mm A-scans x 0.6 mm) containing SC centered at CC ostia were recorded. Contrast and magnification were adjusted to maximize visualization. SC ostia cross-sectional area was measured by manually tracing in ImageJ (ImageJ 1.40g, http://rsb.info.nih.gov/ij/). Mean Doppler shift was calculated as ½ of measured maximum within the adjoined CC. Velocity angle and CC diameter at the point of Doppler measurement were used to calculate volumetric aqueous outflow within the CC. Flow, CC diameter, and velocity were compared with ostia area by linear regression.

 

Results:

 

Aqueous outflow (mean ± SD) in individual CC’s was 0.042 ± 0.05 µl/min, with velocity and diameters of 3.1 ± 2.0 mm/s and 0.015 ± 0.008 µm respectively. No significant correlations between ostia area and CC flow parameters were detected (Figure).

 

Conclusions:

 

Individual CC flows measured using our non-invasive technique were in excellent agreement with published values using invasive techniques. Aqueous outflow within individual CC’s appears to be independent of the cross-sectional area of the ostia of its origin. There was no relationship detected between collector channel diameter (A), aqueous outflow velocity with the collector channel (B), or aqueous outflow (C) and Schlemm’s canal ostia area.  

 

References:

 

Moses RA: Circumferential flow in Schlemm's canal. Am J Ophthalmol 88:585, 1979.

 

Keywords: aqueous • imaging/image analysis: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)