Comparison of clinical and spectral domain optical coherence tomography optic disc margin anatomy

To investigate spectral domain optical coherence tomography (SD-OCT)-detected optic disc margin anatomy in the monkey eye by colocalizing disc photographs to SD-OCT scans acquired from the same eyes.

The neural canal opening (NCO) was delineated within 40 digital radial sections generated from SD-OCT volumes acquired from 33 normal monkey eyes (15 degrees, 290 x 768 horizontal grid pattern). Each volume was colocalized to its disc photograph by matching the retinal vessels within each photograph to vessel outlines visible within en face SD-OCT images. Border tissue was delineated where it extended internally to the NCO. A clinician (masked to delineated points) marked the disc margin onto each photograph while viewing the relevant stereophotograph pair. Alignment of the clinician-ascribed disc margin to the NCO and border tissue delineation was assessed. The process was repeated in a single myopic human eye.

In 23 eyes, the NCO aligned to the disc margin. In 10 eyes, externally oblique border tissue was detectable in the temporal disc. In these regions of the disc, the termination of border tissue was the disc margin. An exaggerated form of this phenotype was observed in the myopic human eye. In this case, temporal border tissue terminated at the anterior scleral canal opening, which was detected as the disc margin.

The termination of Bruch's membrane, border tissue, and the anterior scleral canal opening may constitute the disc margin within the same eye, depending on the border tissue architecture; this anatomy is consistently visualized by SD-OCT.