Comparison of Peripapillary Retinal Nerve Fiber Layer Thickness, Functional Subzones, and Macular Ganglion Cell-Inner Plexiform Layer in Differentiating Patients With Mild, Moderate, and Severe Open-angle Glaucoma

Alteration of neurofilament heavy chain and its phosphoforms reveals early subcellular damage beyond the optic nerve head in glaucoma

Background

Retinal ganglion cells (RGCs) axon loss at the site of optic nerve head (ONH) is long believed as the common pathology in glaucoma since different types of glaucoma possessing different characteristic of intraocular pressure, and this damage was only detected at the later stage.

Methods

To address these disputes and detect early initiating events underlying RGCs, we firstly detected somatic or axonal change and compared their difference in acute and chronic phase of primary angle-closed glaucoma (PACG) patient using optical coherence tomography (OCT), then an axonal-enriched cytoskeletal protein neurofilament heavy chain and its phosphoforms (NF-H, pNF-H) were utilized to reveal spatio-temporal undetectable damage insulted by acute and chronic ocular hypertension (AOH, COH) in two well characterized glaucoma mice models.

Results

In clinic, we detected nonhomogeneous changes such as ONH and soma of RGCs presenting edema in acute phase but atrophy in chronic one by OCT. In AOH animal models, an increase expression of NF-H especially its phosphorylation modification was observed as early as 4 h before RGCs loss, which presented as somatic accumulation in the peripheral retina and at the sites of ONH. In contrast, in microbeads induced COH model, NF-H and pNF-H reduced significantly, these changes firstly occurred as NF-H or pNF-H disconnection at ONH and optic nerve after 2 weeks when the intraocular pressure reaching the peak; Meanwhile, we detected aqueous humor pNF-H elevation after AOH and slight reduction in the COH.

Conclusion

Together, our data supports that early alteration of NF-H and its phosphoforms would reveal undetectable subcellular damage consisting of peripheral somatic neurofilament compaction, impaired axonal transport and distal axonal disorganization of cytoskeleton beyond the ONH, and identifies two distinct axonal degeneration which were Wallerian combination with retrograde degeneration in acute PACG and retrograde degeneration in the chronic one.

Reproducibility of Retinal Nerve Fiber Layer and Macular Thickness Measurements Using Spectral Domain Optical Coherence Tomography

The objective of the research was to assess the reproducibility of retinal nerve fiber layer (RNFL) and macular thickness using spectral domain optical coherence tomography and to establish whether the same investigator can get the same or similar results when performing the scan thrice in an hour, without reference to the previous scan and the repeat function. Materials and Methods. In this prospective observational study, 200 subjects who fulfilled the inclusion and exclusion criteria were scanned 3 times according to predefined guidelines at 0, 30 and 60 minutes on the same day, by the same investigator, using spectral domain optical coherence tomography for measurements of RNFL and macular thickness; observations were statistically analyzed and correlated. Results. In RNFL thickness, the temporal sector showed the worst reproducibility as compared to other sectors. RNFL was the greatest in the superior quadrant and the thinnest in the temporal quadrant. For macular thickness, the temporal sector (mid zone) showed the worst reproducibility, while in the outer zone, the inferior sector showed the worst reproducibility; macular thickness was the thinnest at the central zone (innermost 1-mm ring), the thickest within the inner 3-mm ring and diminished peripherally. Conclusions. RNFL and macular thickness measurements using spectral domain optical coherence tomography by the same observer at 0, 30 and 60 minutes were very reproducible, except for the sectors specifically mentioned. The greater the thickness of the RNFL in any sector the better was the reproducibility in that sector. For macular thickness, the temporal sector (mid zone) showed the worst reproducibility.