1. The edge of the scan is cut off: In this situation, the data is incomplete because the scan is incomplete.
One most likely cause of this is head movement during the scan.
The problem is that the machine will give you a measurement for the rest of the scan anyway.
2. Motion artefacts: This is data distortion that results from the patient moving during the scan. In this particular artefact, the patient moves so much that parts of the scan may fall outside of the rectangular display box on the printout.
The resulting data is generally not usable. If thereu2019s a motion artefact, the retinal nerve fibre layer may appear to zigzag.