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10 Screening for refractive surgery
10.8 Displaced apex
This is a 4 Maps Selectable display of a normal astigmatic eye with a thick cornea (644 μm)
(Figure
66). The anterior elevation map shows a "displaced apex" (displaced inferiorly). This causes
the curvature map (anterior tangential curvature) to show an asymmetric pattern. Curvature is a
reference-based measure. An asymmetric curvature pattern can occur with a completely normal
astigmatic cornea when the apex, line of sight and measurement axis do not line up. This is a normal
variant and in itself not indicative of pathology.
DIAGNOSIS - normal astigmatic eye with a false positive "asymmetric bowtie" on curvature
Figure 66: 4 Maps Selectable showing a displaced apex
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