Laminar Microarchitecture (LMA) Change in the Non-human Primate (NHP) Unilateral early Experimental Glaucoma (EG) Model

Abstract

 

Purpose:

 

We have reported profound deformation [IOVS. 2011; 52:345-363] and remodeling [IOVS 2009;50:681-690 and IOVS 2011;52:7109-7121] of the optic nerve head (ONH) connective tissues in NHP EEG. We now compare the regional distribution of lamina cribrosa beam diameter (BD), pore diameter (PD), connective tissue volume (CTV) and connective tissue volume fraction (CTVF) within digital 3D ONH reconstructions of 9 normal and 9 EEG NHP eyes.

 

Methods:

 

ONH reconstructions from both eyes of 9 rhesus NHPs with unilateral EEG were 3D-aligned to a clinical image and the lamina cribrosa was 3D segmented [IEEE Trans Med Imag, 2006; 25:245-255]. Each voxel was assigned a "diameter" value based upon the largest sphere that fit inside the "beam" or "pore" in which it was contained. CTV was defined to be the total volume of beam voxels. CTVF was defined to be the ratio of CTV to total volume (pore + beam voxels). For each ONH, BD, PD, CTV and CTVF data were digitally converted to right eye orientation and mapped to a cylinder of radius 1.5 mm and 120 um thickness. Data were regionalized by clock hour using the BMO-centroid to foveal axis as the horizontal midline allowing direct comparisons between eyes with varying laminar and scleral geometries. For each parameter, regional differences between the normal and EEG ONHs were assessed within generalized estimating equation models.

 

Results:

 

Significant (p<.001) increases in average BD (8%), PD (7.7%) and CTV (81.7%) were present within the 9 EEG vs the 9 normal eyes. Individual EEG change ranged from 2.8% to 23.2% for BD, 2.5% to 18.6% for PD, 39.4% to 142% for CTV and -11.6% to 23% for CTVF. Overall change by clock hour was greatest for BD and PD inferior nasally, for CTV superior temporally; and for CTVF inferior nasally (increased) and temporally (decreased). In general, peripheral change exceeded central change for all parameters.

 

Conclusions:

 

These data expand our previous characterizations of LMA change in NHP EEG [Roberts, et al (above) and Grimm et al, (ARVO, 2007)] to 9 EEG animals. While the patterns of change within these EEG eyes are individual eye specific, (data not shown), our summary figures suggest the peripheral inferior nasal and superior temporal clock hours to be the sites of greatest EEG alteration.  

 

Keywords: optic nerve • lamina cribrosa • imaging/image analysis: non-clinical