In OCT, what does an A-scan represent?

• A. A cross-sectional image of the retina.
• B. A line of depth information along a single axis.
• C. A color channel.
• D. A two-dimensional map.

Answer: (B)

An A-scan is a depth profile along a single line. In OCT it records how the backscattered light varies with depth at one lateral position, giving a one-dimensional plot of reflectivity versus depth (in micrometers). The bright peaks correspond to tissue boundaries where refractive index changes cause strong reflections. When many A-scans are collected across positions and stacked, they form a B-scan, which is a two-dimensional cross-sectional image of the tissue. A color channel is not used in this depth profile, and a two-dimensional map implies imaging over an area, which comes from combining multiple A-scans into a B- or en-face view, not from a single A-scan.