How the PASCAL Tonometer works

PASCAL is always ready for operation; simply swivel it into place
before the patient’s eye, zero the pressure sensor with a single click
of the Blue Knob, advance the SensorTip to rest against the patient’s
eye. After a few seconds a sound will tell you that sufficient data
have been collected. Pull back now, and immediately you will see the
numerical result, precise and unambiguous, on the PASCAL’s
illuminated LCD display.
When the concave surface of the SensorTip touches the corneal
surface, a solid-state piezoresistive pressure sensor, built flush with
the center of the tip surface, directly measures IOP across the
cornea. The contoured surface of the SensorTip has been calculated
to generate minimal distortion of the cornea (contour matching) and
hence minimize tension forces within the cornea during a
measurement.
The PASCAL can be mounted on any slitlamp and is advanced
towards the patient’s eye by using the slitlamp’s joystick. The
SensorTip is mounted on a spring-loaded Cantilever which provides a
constant appositional force against the cornea of 1 gram, eliminating
any concern of over-compressing the cornea as is possible with other
tonometers.
The pressure in the eye is detected 100 times per second and is
digitized and stored in the PASCAL’s memory. A built-in
microprocessor determines the intra-ocular pressure (IOP) and its
pulsatile fluctuations caused by the patient’s heartbeat (ocular pulse
amplitude, or OPA). The IOP and OPA are displayed as numeric values
on the LCD display, along with a Q score which reflects the quality of
the data obtained during the measurement.
The Ocular Pulse Amplitude (“an often overlooked jewel of
information”) provided by the PASCAL may furnish additional
clinically useful information pertaining to ocular perfusion and its
potential relation to ocular, and even systemic, diseases. However,
the clinical relevance of OPA and ocular blood flow is not yet fully
understood and warrants further clinical investigation. Early evidence
appears to show that a low OPA (poor ocular perfusion) is a risk
factor for progression of visual field loss in patients already diagnosed
with glaucoma. Significantly different OPAs between eyes could
indicate carotid obstructive disease.