Design concepts, Pulsair intelliPuff®

Background to the development of Pulsair intelliPuff

Although the Pulsair EasyEye provided excellent clinical results and proved to be a major step forward in both ease of use and user acceptability, our primary goal in its redesign was to completely surpass it with an entirely new model that will provide even greater accuracy, patient comfort and speed of use.  In addition our development team singled out its weight and size as being in need of a slimming programme. Users are looking for as small a ‘footprint’ as possible and our distributors for even lower shipping charges.  From the patient’s perspective we targeted ourselves to reduce the puff intensity and duration to such a level it will be hardly noticed.

From the onset of the project we were totally focused on our key objective; starting from the patient and working back through the system and user interface to the user to achieve a truly remarkable Tonometer.   The challenge of generating a virtually unnoticeable puff without compromising – indeed improving accuracy proved to be a challenge that involved evaluating and changing virtually all the variables related to the puff.  Having achieved the softest and ‘shortest’ puff possible we turned our attention to the pump, completely redesigning it and its housing and sound insulation properties making the system virtually silent.  Whilst the optical and mechanical designs were being fine tuned the software engineers were completely re-writing the user interface and the calibration algorithms to give users more flexibility and greater accuracy.

Principle of operation

Air impulse tonometry is a variant of the general applanation tonometry in which a portion of the cornea is flexed by mechanical stimuli in which the force/pressure required to produce the flexing effect is related to the intraocular pressure.  The air puff technique requires directing a calibrated quantized packet of air towards the central portion of the cornea, and the detection of the pre-defined deformation of the cornea through optical means and reflections from the corneal surface.

Keeler Pulsair intelliPuff subsystems
Air impulse tonometry is an extremely complex process. Reliable, repeatable and accurate objective tonometry relies upon the performance of two critical subsystems:

Position detection: 
It is important that the instrument knows its position and orientation relative to the eye being measured.  When an air packet is released towards the cornea, the release position and the direction of the air travel have significant effect on the reaction of the cornea to the puff and therefore the measurement result.

This position detection in the case of a hand-held instrument in which neither the patient’s eye nor the operator’s movements are restricted becomes of critical importance.  In the latest Keeler instrument this is carried out through the use of 3 optical sensors working at infra-red wavelength.  A continuously monitored and controlled LED infra red light source provides a precisely directed beam whose reflection from cornea is registered by the 3 sensors.  These sensors provide the critical alignment data related to the distance, pitch and the alignment of the instrument from the cornea.  The signals are converted to digital form at rates of up to 100K bytes per second.  It is the intelligent processing of these signals which enable the on-board processor to calculate precisely the instruments position relative to the patient’s eye every fraction of a millisecond thus allowing an event (air release) only when alignment is perfect.

The quantized “air puff”:
Here, our instrument design departs from the more conventional motor/rotary-actuator driven piston for generation of the air puff.  In a hand-held instrument it is of paramount importance that the measurement is carried out in the shortest possible time, reducing the possibility of hand/eye movement which can lead to errors in the measurement.  Following extensive research at Keeler, we have perfected a pressurised plenum chamber and solenoid-valve technique which enables the instrument to perform its measurement within a maximum period of 10ms of data capture (typically 3ms).   Accurate control and measurement of the reservoir pressure together with high speed measurement of each individual generated air puff and the tracking of individual solenoid valve characteristic has enabled the instrument to achieve repeatability of operation well beyond that experienced in instruments of this type in the past.

The real power of Pulsair intelliPuff

Software and the user interface
The technology behind the intelliPuff is delivered to the user via a totally new software and user control interface. With devices of this nature there is a direct relationship between ‘ease of use’ and the repeatability and accuracy of the results; intelliPuff allows the user to select between two modes of use depending on the patient and working environment; clinical  mode or automatic mode are software and user selectable.
intelliPuff software allows the user to automate the firing sensitivity – initially assessing the event position for clinical mode, the software will detect any difficulty in achieving firing criteria and automatically switch to the most appropriate sensitivity for the patient and user. 
To further speed the measurement process an audible signal will indicate when sufficient readings have been taken for that eye. The OD/OS button has been re-positioned below the users thumb for rapid switching between eyes. 
The intelliPuff software continuously evaluates the results and will eliminate ‘outliers’ from the displayed result.  An additional feature to take advantage of our significantly increased accuracy is that users can select the display mode to measure IOP in either 1mmHg or 0.1mmHg increments.

Surely all “air puff” Tonometers work the same way?

No

The Keeler intelliPuff uses 21st century technology to deliver ultra reliable, repeatable and accurate IOP measurements.