Abstract
Purpose: :
To report the planarity of BMO within 3D Histomorphometric and 3D spectral domain optic nerve head (ONH) OCT reconstructions of 52 normal NHP eyes.
Methods: :
BMO was delineated within 40 radial (4.5º interval), digital sagittal sections (IOVS 2007; 48:3195-3208) of 3D histomorphometric reconstructions (IOVS 2004; 45:4388-4399) of 38 normal ONH of 38 NHPs each perfusion fixed at IOP 10 mm Hg and 14 non-interpolated, Heidelberg Spectralis (Heidelberg Engineering, Heidelberg, Germany) 3D OCT volumes of 14 normal eyes of 14 living NHPs. Within all 52 reconstructions, a least-squares ellipse (BMO ellipse) was fitted to the 80 BMO points (2 per radial section) and BMO planarity was assessed by calculating the plane error (average distance of the 80 BMO points to the plane defined by the BMO ellipse) relative to the major and minor dimensions of the ellipse.
Results: :
Median Plane error was similar within the Histomorphometric and OCT volumes (8 µm, range 4 µm to 14 µm, Histomorphometric and 11 µm, range 6 µm to 27 µm, OCT) and were small relative to the magnitude of the ellipse. Median histomorphometric ellipse dimensions were 1439 µm (major ellipse, range 1214 µm to 1735 µm) and 1044 µm (minor ellipse range, 808 µm to 1263 µm). Median OCT ellipse dimensions were 1807 µm (major ellipse range, 1519 µm to 2064 µm) and 1290 µm (minor ellipse range, 975 µm to 1432 µm). While OCT delineated BMO points were more irregular (relative to the clinically visible disc margin), planarity within both the Histomorphometric and OCT volumes were similar.
Conclusions: :
BMO planarity within Histomorphometric and OCT 3D ONH reconstructions support the use of a BMO zero-reference plane for cross-sectional and longitudinal ONH and peripapillary nerve fiber layer quantification. The observed reduction in histomorphometric ellipse dimensions compared to OCT is most likely a consequence of tissue shrinkage during tissue fixation and embedding.