What anatomical reference is used for the posterior fundus during a B-scan?

The posterior fundus during a B-scan is consistently referenced to the optic nerve. This anatomical structure serves as a key landmark in ophthalmic ultrasound as it provides a stable point from which to assess the surrounding structures, including the retina, macula, and other retinal layers.

Using the optic nerve as a reference helps sonographers accurately locate and visualize various features of the posterior segment of the eye, including pathology like retinal detachments or tumors. Its position is relatively consistent among patients, allowing for standardized imaging techniques and facilitating comparisons between different examinations.

Other structures such as the macula, fovea, and retinal pigment epithelium, while important for evaluation, do not provide the same level of reliable reference as the optic nerve due to variations in their anatomy across individuals. Thus, the optic nerve stands out as the most critical anatomical reference point in this context.