Effect of radial B-scan density on longitudinal Minimum Rim Width (MRW) change detection in Non-Human Primate (NHP) Experimental Glaucoma (EG)

Abstract

 

Purpose

 

To determine the effect of reducing the density of acquired Spectral Domain Optical Coherence Tomography (SDOCT) Optic Nerve Head (ONH) radial B-scans on global and sectoral minimum rim width (MRW) change detection in NHP EG.

 

Methods

 

Both eyes of 8 monkeys (4.4-26.1yrs) underwent SDOCT ONH imaging 5-10 times at baseline, then biweekly following laser-induced, unilateral intraocular pressure (IOP) elevation until the onset of electroretinography-detected functional change in the EG eye. For each imaging session, ONH images were acquired 30 minutes after manometric IOP lowering to 10 mmHg. ONH landmarks were delineated in 40 SDOCT radial B-scans at each time-point. For each EG eye, MRW was calculated globally and within twelve 300 sectors oriented relative to the Foveal-BMO (FoBMO) axis¹ using all 40, or 20, 16, 8 and 4 B-scans equally spaced around the ONH, at each time point. Eye-specific MRW onset required MRW change to exceed the baseline 95% confidence interval of variability and also be confirmed on two subsequent tests. Global and 300 sectoral MRW change onset was then determined for each EG eye for each scan-set and compared to 40 B-scan onset.

 

Results

 

Within the 40 B-scan volumes, MRW onset occurred globally and within 5 sectors (4-7,11) for all 8 EG eyes. Six eyes achieved MRW onset in all 12 sectors. Reducing the number of B-scans to 20 had minimal effect on MRW onset-time, except in some cases (Figure 1). Globally, MRW onset-time for all 8 eyes differed only when the scan-sets were reduced to 16 and 4, respectively (Table 1) The majority of sectors (85.4%) had identical onset-times in all 8 EG eyes when 40 and 20 B-scans were used, and only 9.4% of sectoral onset-times were delayed by more than 20 days when 20 instead of 40 B-scans were analyzed (Table 1). In all cases the 20-scan data deviated by less than 8 μm from the 40-scan data at the 20-scan time of onset detection.

 

Conclusions

 

These results suggest that 20 radial ONH B-scans may demonstrate MRW onset performance that is clinically indistinguishable from 40 radial ONH B-scans in NHP EG. An assessment of the effect of reduced B-scan density on specificity is underway in the fellow control eyes.<br /> <br /> 1. He L et al. PLoS One. 2014 Mar 18;9(3):e92225