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Experimental Glaucoma Causes Optic Nerve Head Neural Rim Tissue Compression: A Potentially Important Mechanism of Axon Injury

View Article: PubMed Central - PubMed

ABSTRACT

Purpose: We tested the hypothesis that experimental glaucoma (EG) results in greater thinning of the optic nerve head (ONH) neural rim tissue than the peripapillary retinal nerve fiber layer (RNFL) tissue.

Methods: Longitudinal spectral-domain optical coherence tomography (SDOCT) imaging of the ONH and peripapillary RNFL was performed every other week under manometric IOP control (10 mm Hg) in 51 nonhuman primates (NHP) during baseline and after induction of unilateral EG. The ONH parameter minimum rim area (MRA) was derived from 80 radial B-scans centered on the ONH; RNFL cross-sectional area (RNFLA) from a peripapillary circular B-scan with 12° diameter.

Results: In control eyes, MRA was 1.00 ± 0.19 mm2 at baseline and 1.00 ± 0.19 mm2 at the final session (P = 0.77), while RNFLA was 0.95 ± 0.09 and 0.95 ± 0.10 mm2, respectively (P = 0.96). In EG eyes, MRA decreased from 1.00 ± 0.19 mm2 at baseline to 0.63 ± 0.21 mm2 at the final session (P < 0.0001), while RNFLA decreased from 0.95 ± 0.09 to 0.74 ± 0.19 mm2, respectively (P < 0.0001). Thus, MRA decreased by 36.4 ± 20.6% in EG eyes, significantly more than the decrease in RNFLA (21.7 ± 19.4%, P < 0.0001). Other significant changes in EG eyes included increased Bruch's membrane opening (BMO) nonplanarity (P < 0.05), decreased BMO aspect ratio (P < 0.0001), and decreased MRA angle (P < 0.001). Bruch's membrane opening area did not change from baseline in either control or EG eyes (P = 0.27, P = 0.15, respectively).

Conclusions: Optic nerve head neural rim tissue thinning exceeded peripapillary RNFL thinning in NHP EG. These results support the hypothesis that axon bundles are compressed transversely within the ONH rim along with glaucomatous deformation of connective tissues.

No MeSH data available.


Longitudinal change for other ONH parameters. Box plots represent the distribution (median, interquartile range, and extremes, N = 51) of raw parameter values in CTL eyes and eyes with EG at BL (hatched boxes) and at the final imaging session (filled boxes). (A) MRA angle. (B) BMO area. (C) BMO nonplanarity. (D) BMO aspect ratio. The P values listed represent the results of a paired t-test in each case (comparing EG eyes at the final imaging session to their own BL and separately to their fellow control eyes at the final session; P values in red font indicate statistical significance).
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i1552-5783-57-10-4403-f06: Longitudinal change for other ONH parameters. Box plots represent the distribution (median, interquartile range, and extremes, N = 51) of raw parameter values in CTL eyes and eyes with EG at BL (hatched boxes) and at the final imaging session (filled boxes). (A) MRA angle. (B) BMO area. (C) BMO nonplanarity. (D) BMO aspect ratio. The P values listed represent the results of a paired t-test in each case (comparing EG eyes at the final imaging session to their own BL and separately to their fellow control eyes at the final session; P values in red font indicate statistical significance).

Mentions: Finally, as described in Figure 1 for the individual example EG eye, there were subtle changes for other ONH parameters as well, such as a decrease of the MRA angle (whereby it became significantly more acute at the final session in EG eyes, Fig. 6A), a significant increase in the BMO nonplanarity (whereby the BMO became less planar and more “bowed” into a saddle shape, Fig. 6C) and a significant decrease in the BMO aspect ratio (i.e., the aspect ratio of the best 3D-fit of an ellipse to the BMO, which became rounder, Fig. 6D). However, there was no significant change in the area of the BMO projection (Fig. 6B).


Experimental Glaucoma Causes Optic Nerve Head Neural Rim Tissue Compression: A Potentially Important Mechanism of Axon Injury
Longitudinal change for other ONH parameters. Box plots represent the distribution (median, interquartile range, and extremes, N = 51) of raw parameter values in CTL eyes and eyes with EG at BL (hatched boxes) and at the final imaging session (filled boxes). (A) MRA angle. (B) BMO area. (C) BMO nonplanarity. (D) BMO aspect ratio. The P values listed represent the results of a paired t-test in each case (comparing EG eyes at the final imaging session to their own BL and separately to their fellow control eyes at the final session; P values in red font indicate statistical significance).
© Copyright Policy - cc-by-nc-nd
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016000&req=5

i1552-5783-57-10-4403-f06: Longitudinal change for other ONH parameters. Box plots represent the distribution (median, interquartile range, and extremes, N = 51) of raw parameter values in CTL eyes and eyes with EG at BL (hatched boxes) and at the final imaging session (filled boxes). (A) MRA angle. (B) BMO area. (C) BMO nonplanarity. (D) BMO aspect ratio. The P values listed represent the results of a paired t-test in each case (comparing EG eyes at the final imaging session to their own BL and separately to their fellow control eyes at the final session; P values in red font indicate statistical significance).
Mentions: Finally, as described in Figure 1 for the individual example EG eye, there were subtle changes for other ONH parameters as well, such as a decrease of the MRA angle (whereby it became significantly more acute at the final session in EG eyes, Fig. 6A), a significant increase in the BMO nonplanarity (whereby the BMO became less planar and more “bowed” into a saddle shape, Fig. 6C) and a significant decrease in the BMO aspect ratio (i.e., the aspect ratio of the best 3D-fit of an ellipse to the BMO, which became rounder, Fig. 6D). However, there was no significant change in the area of the BMO projection (Fig. 6B).

View Article: PubMed Central - PubMed

ABSTRACT

Purpose: We tested the hypothesis that experimental glaucoma (EG) results in greater thinning of the optic nerve head (ONH) neural rim tissue than the peripapillary retinal nerve fiber layer (RNFL) tissue.

Methods: Longitudinal spectral-domain optical coherence tomography (SDOCT) imaging of the ONH and peripapillary RNFL was performed every other week under manometric IOP control (10 mm Hg) in 51 nonhuman primates (NHP) during baseline and after induction of unilateral EG. The ONH parameter minimum rim area (MRA) was derived from 80 radial B-scans centered on the ONH; RNFL cross-sectional area (RNFLA) from a peripapillary circular B-scan with 12° diameter.

Results: In control eyes, MRA was 1.00 ± 0.19 mm2 at baseline and 1.00 ± 0.19 mm2 at the final session (P = 0.77), while RNFLA was 0.95 ± 0.09 and 0.95 ± 0.10 mm2, respectively (P = 0.96). In EG eyes, MRA decreased from 1.00 ± 0.19 mm2 at baseline to 0.63 ± 0.21 mm2 at the final session (P < 0.0001), while RNFLA decreased from 0.95 ± 0.09 to 0.74 ± 0.19 mm2, respectively (P < 0.0001). Thus, MRA decreased by 36.4 ± 20.6% in EG eyes, significantly more than the decrease in RNFLA (21.7 ± 19.4%, P < 0.0001). Other significant changes in EG eyes included increased Bruch's membrane opening (BMO) nonplanarity (P < 0.05), decreased BMO aspect ratio (P < 0.0001), and decreased MRA angle (P < 0.001). Bruch's membrane opening area did not change from baseline in either control or EG eyes (P = 0.27, P = 0.15, respectively).

Conclusions: Optic nerve head neural rim tissue thinning exceeded peripapillary RNFL thinning in NHP EG. These results support the hypothesis that axon bundles are compressed transversely within the ONH rim along with glaucomatous deformation of connective tissues.

No MeSH data available.