Sequential Imaging of Schlemm’s Canal and the Collector Channels in Normal and POAG Eyes

Abstract

 

Purpose:

 

To quantitatively and qualitatively evaluate the morphology of Schlemm’s canal (SC) and the collector channels (CC) in normal and POAG eyes through sequential imaging using anterior segment Fourier-domain OCT (ASFDOCT)

 

Methods:

 

15 normal subjects with no ocular pathology (N group) and 15 POAG patients (G group, no intraocular surgeries, abnormal 24-2 perimetry, untreated IOP >21mmHg, CDR >0.6) were imaged on the right temporal limbus. The initial set consisted of 15 radial and 5 longitudinal scans. When a collector channel was identified, additional sequential scans were performed in order to follow its course and composite images were created. SC cross-sectional area, minimum and maximum width, index of variability, ostium diameter, and mean diameter of the CC were compared using a T test. Correlations between the morphometry of SC/CC and the maximum and treated IOP, CDR and visual field PSD were evaluated using Spearman’s correlation coefficient.

 

Results:

 

The groups were comparable in age (N=64.5 G=65.5 years p=0.77). SC area (N=1530±640 G=1150±376 µm² p=0.06) reached marginal significance. SC length (p=0.003), minimum longitudinal width (p=0.002) and the index of variability (p=0.04) were reduced in the G group. No differences were observed in CC morphometry. A significant negative correlation was observed between SC length (r=-0.38), minimum longitudinal width (r=-0.51) and the maximum IOP. Qualitatively, SC and CC dimensions appeared reduced in both groups. In the G group, SC appeared more tortuous and less intense, suggesting decreased aqueous flow. SC appeared widest at the area of junction with CC, suggesting that circumferential flow is lost before vertical flow.

 

Conclusions:

 

SC and CC can be evaluated in vivo using ASFDOCT. Sequential imaging of SC and CC provided a better assessment of the overall condition of SC and CC. Modifications of SC in eyes with POAG may be better explained as a change in configuration rather than a simple loss of lumen.  

 

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