Reproducibility of Measurements of Aqueous Velocity Within Schlemm’s Canal With Spectral Domain Optical Coherence Tomography

Abstract

 

Purpose:

 

Determine the feasibility and reproducibility of spectral domain optical coherence tomography (SDOCT) velocity measurements within Schlemm’s canal.

 

Methods:

 

A 4.6x4.6x2mm (300x300x1024 pixels) volume of the anterior segment was imaged with a customized SDOCT (Optics: Bioptigen Inc, Durham NC, Lightsource: Superlum, County Cork, Ireland). Doppler measurements were obtained from 4 sequential A-scans obtained at each location, and sampled at 28.571 kHz, resulting in a 12.6 second scan time. Three volumes were obtained from the right eye of 14 healthy subjects. Schlemm’s canal was located within an image, and the identical location was sampled in the Doppler dataset. (Figure) The difference between the Doppler signal recorded in Schlemm’s canal and the surrounding tissue was used to compensate for eye motion. The position of Schlemm’s canal in sequential frames was identified to define its 3D spatial orientation relative to the SDOCT beam, used to angle correct the Doppler measurement.Seven velocity measurements were obtained and averaged for each image. Mean and coefficient of variation were calculated.

 

Results:

 

The velocity of aqueous within Schlemm’s canal was 1.68 ± 0.78mm/s. Measurements ranged from 0.66 to 4.49mm/s. The coefficient of variation of velocity measurement was 45.41%, ranging from 14.73% to 95.99%.

 

Conclusions:

 

Velocity in Schlemm’s canal has been measured non-invasively for the first time. Noise reduction and signal enhancement may improve the utility of the method. Doppler measurements of velocity within Schlemm’s canal may be obtained by SDOCT.  

 

Clinical Trial:

 

www.clinicaltrials.gov NCT00343473

 

Keywords: aqueous • imaging/image analysis: clinical • outflow: trabecular meshwork