Comprehensive Mapping of Ostia Locations Requires Multiple Sectioning Orientations

Abstract

 

Purpose

 

Examination of collector channel ostia within Schlemm canal (SC) has been accomplished using sections radially across and tangentially along SC interchangeably^1,2 (Figure 1). The purpose of this study was to test the hypothesis that optical coherence tomography (OCT) scans circumferentially along and radially across SC produce equivalent maps of collector channel ostia sizes and locations (Figure 2).

 

Methods

 

Eighteen eyes of 18 subjects (12 healthy, 6 glaucomatous; 12 nasal, 16 temporal for 28 scans in total) were imaged by swept-source OCT.³ 600 B-scans, each consisting of 600 A-scans, were obtained across and then along SC in a single volumetric scan. Scans were merged into a single aligned volume⁴, and then sampled across and along SC (Figure 1). Each A-scan stack was interrogated, and ostia mapped on an enface image (Figure 2) by size and locations. Ostia on the maps were counted by size, noting concomitant localizations.

 

Results

 

391 ostia (14.0±5.0 per scan; 7.7±3.2 per orientation) were located throughout all scans, 213 (54% of all ostia) in radial scans across SC, and 216 (55% of all ostia) in circumferential scans along SC. Only 38 (10%) were visualized in both scans across and along SC (Figures 1 and 2; white and black markers respectively).

 

Conclusions

 

Examination of a single scan orientation misses nearly half of the ostia that can be visualized within a merged volume. Comprehensive mapping of ostia locations requires examination of multiple sectioning orientations of a volumetric limbus scan. 1. Johnstone, M.A., et al., Exp Eye Res, 2014. 119: p. 70-6. 2. Battista, S.A., et al.,. Invest Ophthalmol Vis Sci, 2008. 49(12): p. 5346-52. 3. Grulkowski, I., et al., Photonics Lett Pol, 2011. 3(4): p. 132-134. 4. Kraus, M.F., et al., Biomed Opt Express, 2012. 3(6): p. 1182-99.  

 

Figure 1: Circumferential scans along (left) and radial scans across (right) Schlemm canal

 

 

Figure 2: Collector channel ostia located in scans along (black) and across (white) Schlemm canal are mapped on an enface image