OCULUS Pentacam Interpretation Manual page 88

12 Belin/Ambrósio Enhanced Ectasia Display
Keratoconus will show a positive island of elevation, as the conical protrusion is above the BFS. The
location of the island and its magnitude will correspond to the location of the cone and the severity
of the ectatic change.
Figure 105: Elevation map of a keratoconic cornea
Most patients with keratoconus have in addition to a conical cornea a significant amount of
astigmatism and one will typically see a positive island of elevation superimposed on an astigmatic
pattern (Figure 106).
Figure 106: Elevation superimposed on an astigmatic pattern
While the BFS gives easily interpretable qualitative information, early or subtle ectatic change can
at times be hard to visually identify. Part of the reason for this is that the BFS is influenced by the
ectatic region causing the BFS to steepen and partially masking the cone. A modification of the BFS
called the "enhanced reference surface" utilizes the same 8.0 mm central optical zone, but excludes
a small portion of this data surrounding the TP on the cornea, effectively minimizing the cone's
influence on the best-fit reference surface
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(Figure 107).