שאלה משלב א׳ במחלות עיניים · מועד 2021, שאלה 143

Placido-disc topography measures the reflection of concentric rings from the tear film on the anterior corneal surface, so it is affected by anything that alters that reflection or the alignment of the eye: direction of gaze and fixation, tear film quality and dry eye, lid position and lashes, and recent contact lens wear. Axial length, chamber depth and pupil size do not influence the quality of a Placido-based map.

מקור: Kanski p. 13 19