Abstract
Purpose:
To investigate the three dimensional structure of the elastin fiber system (EFS) in the juxtacanalicular (JCT) region of the trabecular meshwork and explore its interactions with SC inner wall (IW) in normal and primary open angle glaucoma (POAG) eyes.
Methods:
SC IW and adjacent EFS were examined using the 2-photon and confocal microscopy (Fluoview FV1000 MPE, Olympus America Inc., Center Valley, PA). Two pair of age matched normal (86,83 years) and POAG eyes (78,83 years) were immersion fixed in 4% paraformaldehyde/0.1M phosphate buffer. Two wedges 180ᵒ apart were isolated from each eye. The SC IW was exposed and tangential IW wedges were labeled with ToPro-3 (nuclei) and CD31 and Alexa Fluor 546 (cell membranes) and imaged in confocal mode. Elastin fibers (autofluorescence upon excitation at 800 nm) and collagen beams (second harmonic generation at 800 nm) were imaged in 2-photon mode. Volumes were analyzed for elastin fiber volume/total volume. Cell membranes were dilated 1 and 2 μm and elastin in these dilations were calculated as a percent of the total elastin in the volume.
Results:
The EFS in the JCT region adjacent to SC is a complex multilayered structure. The EFS occupied 7.2% in normal and 4.9% in POAG eyes. Visible fiber diameters ranged from 0.5-2.0 μm. SC cells aligned to the direction of fluid flow and were buttressed by 2.0 μm fibers which were spaced 2.0-5.0 μm apart. Elastin 2 μm fibers travel at an oblique angle from aligned SC cells and are crossed with 1.0 μm fibers at 90° at 4.0-5.0 μm intervals. In normal eyes, cell dilations containing elastin at 1 μm and 2 μm were 60% and 71%/total EFS volume but in POAG eyes these regions were found to be reduced to 22.8% and 34%/total EFS volume.
Conclusions:
A complex EFS is present in the JCT region of normal and POAG eyes. Decreased total elastin and a decreased number of elastin fibers in close proximity to cell membrane in POAG eyes may disrupt the mechanosensitive environment and contribute to impairment of outflow.