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Are handheld or portable tonometers appropriate for home eye pressure monitoring?

Submitted by dave on Thu, 04/22/2010 - 12:29pm

In any tonometer (based on today's technology), you can have some, but not all of, the following:

  • ease of use
  • accuracy (reliability and validity of data)
  • low cost
  • portability

handheld portable tonometerPeople tend to give a priority to portability and low cost. New products aimed at this feature set have recently been announced. Does it make sense to utilize those devices for self-tonometry?

We have to agree that any trade off that doesn't include reliability and validity of IOP data invalidates the whole endeavor of self-tonometry. Not only is it meaningless to do it if the data is not of sufficient quality upon which to make important decisions, but it could actually be detrimental to do self-tonometry in that case.

With today's technologies, portability entails user-alignment (in the context of self-tonometry). Proper user-alignment to produce a valid measurement, by definition, depends upon user skill as well as various specific conditions of each measurement. User-alignment, regardless of the tonometer, is difficult! (User-alignment is defined as the operator of the tonometer having to align the tonometer with the eye manually. Alignment is a very precise process requiring a steady hand, good eyesight, training and practice.)

Therefore, the requirement of user-alignment conflicts with the requirement of reliability and validity of IOP data. We cannot guarantee reliability and validity of IOP data when variable user skills are required to produce that data.

If any decent ophthalmologist or scientist (or intelligent thinker) considers a set of IOP data, they must consider how the data was obtained. If patient skill played a critical role in producing that data, as it does when user-alignment is required, the clear thinking person will immediately discount that data. Therefore, the self-tonometrist's efforts may not produce much of value.

The conclusion is that the only way to establish self-tonometry as a valid endeavor is to utilize a tonometer that removes user skill from any critical role in producing the valid data. Currently, only fully automatic tonometers meet this standard. No current handheld (i.e., portable or hand held) tonometer meets it. And only one tonometer fully meets the standard of producing the highest quality IOP data without requiring patient skill -- a fully automatic desktop tonometer.

The International Society of Self-Tonometry will likely be creating a standards document for tonometers suitable for home use (self-tonometry). A tonometer used for self-tonometry must be fully automatic to remove user skill from (any critical part of) the measurement process.

However, we may also wish to ask if there are some circumstances where a handheld tonometer could be appropriate. For example,  consider the situation where self-tonometry IOP data collected via a handheld tonometer can supplement IOP data from another more reliable tonometer when:

  • We rigorously establish the individual user's skill via actual tests of such
  • We establish that the data is consistent with other IOP data known to be reliable

Not only is this impossible, it leads to the following unacceptable situation. The most important IOP measurements we can possibly obtain via self-tonometry are the unusual ones, the unexpected ones, the measurements whose value deviates significantly from what was expected (or maybe hoped for). Those are the exact measurements -- if we can trust the data -- that would form the basis for important decisions. And, unfortunately, those are the exact measurements that we would have to disregard if they were collected by any handheld tonometer currently known or conceived. The need to discard such potentially important measurements is true even if we have established user skill and prior consistent data because it is always possible for a skilled user to make mistakes -- even consistently repeated mistakes.

A true example can be seen with a widely advertised handheld tonometer. An individual in our self-tonometry group (a skilled user) took a series of IOP measurements with the handheld tonometer where he unintentionally aligned the tonometer with his eye in such a way as to artificially elevate the tonometer's reported IOP. The series of measurements looked valid and consistent. He could have continued repeating these measurements and obtaining consistent results. Unfortunately, the entire series of measurements was erroneous. He did not (and could not, at the time) have known this fact. It required an external observer to identify the user-alignment error.

We end up with the conclusion that even with skilled users and an established track record of good data collection, we cannot trust self-tonometry IOP data if the correct measurement process depends upon user skill, particularly the skill to manually align the tonometer.

In regard to the [newly released handheld tonometer], my conclusion after testing it is that significant user skill is required to manually align the device. This is true at all times, even after training and even after having an expert adjust the instrument to help the patient properly align it. It is impossible to escape a situation that calls the IOP data into question with this tonometer.

On the other hand, with a fully automatic tonometer, we can trust the accuracy and validity of self-tonometry IOP data just as much as we can trust in-office data collected by a trained medical technician -- because a fully automatic tonometer does not require any user-alignment. Therefore, with a full automatic tonometer, self-tonometry data is on as valid as any other accepted IOP data.

In fact, on the foundation of accurate, reliable, valid data (obtained with a fully automatic tonometer), self-tonometry can then go far beyond anything possible with in-office tonometry or even hospital-based diurnal measurements. Only with home monitoring in real life situations is it possible to gain a complete picture of a patient's IOP patterns.

The experience of the FitEyes self-tonometry community indicates that the ophthalmology field currently suffers from a critical shortage of knowledge concerning the real life behavior of IOP in a typical glaucoma patient. There are tremendous gaps in current knowledge that can, at this time, only be filled in by self-tonometry. But to move forward, we need to ensure that self-tonometry is performed with instruments that are fully automatic and that do not depend upon user-alignment.

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