Eye-specific Onset and Spatial Pattern of Longitudinal Change Detected by Spectral Domain Optical Coherence Tomography (SDOCT) Sectoral Analysis in Non-human Primate (NHP) Early Experimental Glaucoma (EG).

Abstract

 

Purpose

 

It has been reported that global SDOCT-detected optic nerve head (ONH) minimum rim width (MRW) changes occur before retinal nerve fiber layer (RNFL) changes in NHP early EG eyes.¹ This study aims to characterize the onset and spatial pattern of these changes in individual eyes, in order to test the hypothesis that MRW sectoral changes precede and predict the location of the sectoral RNFL change.

 

Methods

 

Both eyes of 8 monkeys (1.4-21.9 yrs) underwent SDOCT ONH/RNFL imaging 3-5 times at baseline, then biweekly following laser-induced, unilateral IOP elevation until the onset of confocal scanning laser tomographic (CSLT) surface change in the EG eye.¹ For each imaging session, ONH/RNFL landmarks were delineated in 40 SDOCT B-scans and ONH MRW and RNFL thickness 1500 μm from Bruch’s Membrane Opening (BMO) centroid (RNLFT1500) were calculated for twelve 300 sectors oriented relative to the Foveal-BMO (FoBMO) axis.^1,2 For each parameter, trend-based change onset time¹ was determined for each control and EG eye sector achieving onset. Summary of the number of eyes reaching sectoral onsets for all 8 control and EG eyes and the days to onset after laser for each control and EG eye were plotted.

 

Results

 

EG eye IOP and axon loss (0-30%) have been previously reported.¹ For the 8 EG eyes considered together, the sectoral pattern of SDOCT MRW and RNFLT1500 onset overlap (Fig 1). However, MRW change was more frequent and more extensive than RNFLT1500 change. MRW onset change occurred most frequently within the superior, inferior and inferior-nasal sectors (Fig 1). Eye-specific change occurred earlier in most sectors (all sectors but 2 sectors in M4) for MRW vs RNFLT1500 (Fig 2). Eye-specific pattern of MRW change qualitative overlap with RNFLT1500 change and did not confine to the superior and inferior sectors.

 

Conclusions

 

Eye-specific, SDOCT 300 sectoral ONH MRW sectoral change occurs earlier and appears more extensive than RNFLT change in NHP early EG. In general, the spatial pattern of earliest MRW change overlaps with RNFLT change and may predict it in future studies of eyes followed for longer duration. Our data support the ONH as a target for early change detection in human ocular hypertension.<br /> 1. He L et al. IOVS 2014;55:574-586.<br /> 2. He L et al. PLoS One. 2014 Mar 18;9(3):e92225.