Purpose: To evaluate the precision of anterior chamber dimensions meas
ured by the 50 MHz Humphrey(R) Ultrasound Biomicroscope, the influence
of various subprocedures, and the importance of clear definition of s
tructures, Methods: Fourty-eight right eyes of 26 normal subjects and
22 glaucoma patients were scanned centrally and at the chamber angle a
t three positions under standardized conditions. Eight different param
eters were measured in angle images and two in images of central corne
a and anterior chamber. Four variance components were calculated, Resu
lts: Measurement of the dearest defined structures had the highest pre
cision. In angle images the precision expressed as the coefficient of
variation was <21%, except for measurement of iris-ciliary process (ra
nge: 3-59%). All subprocedures contributed to the overall variance, im
age to image variation the most. Conclusions: The precision of most me
asured parameters seems reasonable for clinical use. All subprocedures
contributed significantly to the overall variance. The parameters tha
t were related to clearly defined structures had the highest precision
.