Asymmetric corneal toricity and pseudokeratoconus in videokeratography.
BACKGROUND
The diagnosis of asymmetric corneal toricity in video- keratography is based on the occurrence of an asymmetric bow tie pattern in the corneal map, which is usually attributed to corneal radial asymmetry but can be an artifact produced by misalignment of the videokeratograph with the corneal apex.


METHODS
This study determined whether asymmetric bow tie patterns in 16 subjects (ages 24 to 40 years with corneal toricity of 0.37 to 1.50D) could be converted to symmetric bow tie patterns by changing the alignment of the videokeratograph so that it was directed at the corneal apex.


RESULTS
In changing from regular to apex alignment the corneal map became more symmetric in 11 eyes, had no change in 3 eyes and increased in 2 eyes. No radius change could be measured centrally, but there were significant changes of greater than 1.00D in the peripheral corneal radii of 8 eyes.


CONCLUSIONS
An asymmetric or angled bow tie appearance of a corneal map suggests a decentered apex rather than corneal asymmetry and may lead to a misdiagnosis of the type or magnitude of corneal toricity, keratoconus or other corneal irregularities.
School of Optometry, University of California, Berkeley 94720-2020, USA.
R B
RB
Mandell
C S
CS
Chiang
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L
Yee
D000328:Adult; D003315:Cornea / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007640:Keratoconus / Q000175:diagnosis*