ABSTRACTEffects of different cornea to instrument distances were assessed by making paired measurements on significantly astigmatic corneas. Differences in pressure noted for the differences in corneal radii were small (less than 0.5 mm of Hg) and none proved statistically significant. The small differences observed were consistent with a hypothesis that a parabolic relationship exists between working distance and NCT pressure reading. That relationship predicts that an error as large as 1.0 mm of Hg would occur only for a few eyes with very flat corneas.