Abstract
Purpose: :
To determine whether three-dimensional micro computed-tomography (micro-CT) can be used to study the human aqueous outflow pathway.
Methods: :
The anterior segment of a normal human eye (age 88) was immersion fixed in 4% paraformaldehyde, divided into 5 sections, immersed in 2% osmium tetroxide, transferred to formol saline, and scanned at 6 and 20 µm voxel resolutions using a 3-D X-ray micro-CT system developed at the Mayo Clinic. 3-D volume images were transferred into ANALYZETM software program for analysis. In each volume, Schlemm’s canal, collector channels and associated vessels were located and studied. Numbers of collector channels were noted and orifice sizes and collector channel diameters were measured.
Results: :
In wedges scanned at 6 µm voxel size, Schlemm’s canal, collector channels, intrascleral and episcleral venous plexuses were observed. Connections between these structures were visible. Septa in Schlemm’s canal were observed. Collector channels were unevenly distributed within and between sections. A total of 24 collector channels were clearly patent and could be readily identified. These channels had an orifice size of 37 ± 13 µm (mean ± SD; range 10 - 60 µm). Collector channel diameter was 23 ± 12 µm (mean ± SD; range 10 - 60 µm). Total length of Schlemm’s canal observed was 33.2 mm. Two collector channels were observed which joined the same vessel adjacent to Schlemm’s canal in several different sections. Collector channels were also observed joining intrascleral vessels which extended into the episcleral region. Images generated at 20 µm did not provide sufficient resolution to study all the indicated structures.
Conclusions: :
3-D X-ray micro-CT is a powerful non-invasive imaging technology that can be readily used to study the 3-D structure and inter-relationships between the components of the aqueous outflow system within the anterior chamber of the fixed human eye.
Keywords: trabecular meshwork • imaging/image analysis: non-clinical • outflow: trabecular meshwork