Watters G A, Owens H
Department of Optometry and Vision Science, University of Auckland, New Zealand.
Optom Vis Sci. 1998 Sep;75(9):640-6. doi: 10.1097/00006324-199809000-00018.
The absolute accuracy of videokeratoscope (VKS) mapping of keratoconus is still in question, with contact lens-induced corneal warpage and chalazion having been shown to resemble this condition closely. Corneal thinning is investigated as a further aid to the diagnosis and description of keratoconus.
The diagnosis of keratoconus in 41 individuals was verified by measuring the corneal thickness difference (I-S difference) between two disparate corneal locations, one inferior to (I) and one superior to (S) the corneal apex, using a Humphrey model 870 Ultrasound pachometer. Corresponding measures of I-S radii were made using radius values obtained from the EyeSys VKS.
A comparison between I-S pachometry and I-S radius demonstrated a marginally increased sensitivity for the latter measurement. Using 95% confidence levels from normative pachometric data, classification of severity of keratoconus is proposed as follows: (1) keratoconus suspect/early keratoconus: I-S pachometry 75 to 100 microns; (2) moderate keratoconus: 100 to 125 microns; and (3) advanced keratoconus: > 125 microns.
I-S pachometry can be used as a descriptor of keratoconus.
