COMPUTERIZED VIDEOKERATOSCOPES

Limitations and Sources of Error:     Instrument Design

The shape and size of the Placido’s 
disc pattern has an affect of the 
accuracy and repeatability of the 
data.  Some instruments have used 
a small pattern which is positioned 
very close to the cornea (Tomey 
Topographic Modeling System for 
example).  This small pattern allows 
a large area of the cornea to be 
covered by the reflected pattern 
but results in more errors in 
focusing and alignment.

A larger pattern (for example on the 
EyeSys 2000 Corneal Analysis System) 
minimizes the focusing and alignment 
problems but may result in the nose 
or brow blocking some of the pattern.