Enhanced Depth Imaging Optical Coherence Tomography of Trabecular Outflow Pathway

Abstract

 

Purpose

 

To assess the usefulness of enhanced depth imaging optical coherence tomography (EDI OCT) for evaluating in vivo microarchitecture of the trabecular outflow pathway.

 

Methods

 

Serial horizontal EDI OCT B-scans were obtained in the nasal and temporal limbal areas from one eye of normal subjects (81 scans per 15x5 degree rectangle; interval between scans, ~35 µm; Fig A and B). The intra- and inter-observer reproducibility of the Schlemm’s canal (SC) cross-sectional area measurement was evaluated using 40 randomly selected EDI OCT scans (8 scans per each of 5 normal eyes). Analysis was based on 3 independent series of re-evaluations made by two observers. The microarchitecture of SC and collector channel (CC) was assessed. For one eye, serial EDI OCT was performed in a radial fashion in every clock hour and 3-dimensional image of the entire SC circumference was reconstructed.

 

Results

 

Eleven normal eyes (11 subjects; mean age, 28±5 years) were included. The SC cross-sectional area measurement by the two observers showed excellent intra- (ICC [intraclass correlation coefficient] = 0.830 for observer 1 and 0.886 for observer 2) and inter-observer (ICC = 0.793) reproducibility (all p<0.001). SC was continuous in the scanned area in all eyes. The cross-sectional shape of SC varied considerably among regions with intermittent bifurcation (Fig C-E). Most CCs were connected to the outer wall of the SC and their locations varied from the medial to the lateral ends of SC (Fig F-H). The entire SC circumference was successfully reconstructed 3-dimensionally (Fig I and J).

 

Conclusions

 

EDI OCT is useful for evaluating the in vivo microarchitecture of the trabecular outflow pathway. This has implications for the development of new drugs and techniques to reduce intraocular pressure.

 

 

(A) 15x5 degree rectangle for 81 serial horizontal EDI OCT B-scans. (B) A horizontal EDI OCT B-scan of the limbus and sclera (red arrow = Schlemm’s canal [SC]). (C-E) SC of various shapes (red dotted lines). (F-H) Collector channels of various locations (yellow arrows). (I and J) 3-dimensionally reconstructed SC (entire circumference and temporal 2.8-mm segment, respectively).

 

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 421 anterior segment • 419 anatomy