-The transducer probe always has a marker, usually a dot, line, or a logo.
-It explains that the upper part of the echogram corresponds to the area where the probe marker is placed.
-3 basic probe orientations are employed to evaluate intraocular lesions in B-scan – Axial, Transverse, and Longitudinal.
Transverse Scan:
-The probe is placed such that the marker is parallel to the limbus.
-Useful for demonstrating the lateral extent of a lesion.
-Depending on the orientation of the probe marker, transverse scans can be horizontal, vertical, or oblique.
-Marker is always oriented towards the nose, while it is always oriented above for vertical and oblique scans.
-The designation of the scan is determined by the meridian that lies in the middle of the scanning section.
-For e.g., in the right eye, if the probe is held horizontally with its face centered on the 6’o’clock meridian, the superior part of the echogram denotes 3’o’clock meridian, the middle of the echogram denotes 12’o’clock meridian, and the inferior part denotes 9’o’clock meridian.
Longitudinal Scan:
-The probe is placed such that the marker is perpendicular to the limbus.
-Hence the beam scans across a single meridian at any given clock hour.
-It shows the anteroposterior extent of the lesion.
-The oriented meridian is the one exactly opposite to the meridian in which the probe is placed.
-For e.g., if the probe placed a 6’o’clock meridian, the picture displayed is the 12’o’clock meridian.
Axial Scan:
-Patient is asked to fix in the primary gaze and the probe is placed on the center of the cornea.
-The sound beam traverses posterior through the center of the lens, intersecting the optic nerve in its path.
-Useful to evaluate the macular region, axial length, and position of lesions in relation to the lens and optic nerve.
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