The pneumatonograph. A laboratory study
R. A. Moses and W. J. Grodzki Jr
The scale reading of the pneumatonograph (PTG) is dependent on the force of
application to the cornea. Since this force is relatively greater at low
intraocular pressure, the scale is compressed, yielding an overestimate of
intraocular pressure in physiologic range. When the PTG is held vertically,
the weight of the plunger is added to the gas propulsion force and the
compression of the scale is accentuated. When a 10-g plunger load is added,
as is advocated for tonography, the scale compression is further
accentuated. We conclude that the PTG scale is compressed, the PTG is
position-sensitive, and that the PTG is totally unsuited to tonography. The
PTG is not an applanation tonometer and should not be confused with
applanation tonometers.
