Non Contact Tonometer

This machine measures intra-ocular pressures, and should be done along with the other "pre-testing" functions (prepping the exam forms, NCT and lensometer) on each patient prior to calling the doc.

When the air puff comes out, it will indent the front surface of the cornea very slightly. The machine measures the amount of indentation via monitoring the change in postion of reflections from the corneal surface. The higher the internal pressure (the harder the eye) the less deflection occurs.

To operate it, first seat the patient and adjust the table height up or down to match the person's chin height (or just a little lower). Have them lean forward and place the chin on the chin-rest, and the forehead along the top bar. This helps to keep the eye and head still, which is necessary to achieve accurate measurement. The NCT is perhaps a little less forgiving as far as lining up the patient, and having an immobile eye is critical. You must also be careful with this instrument to not actually get too close. We definitely do not want to touch the cornea! There is a lock mechanism that can be employed to prevent this, but it must be set differently for each patient, and if done carefully, the readings can be taken without the lock backup.

Start far away from the patient and position the instrument in front of the right eye. Slowly approach the eye until you see two bright round reflections start to converge towards the center. The goal is to get these two to coincide within the central target. Once there, the machine fires the air puff automatically. If the dots actually cross and start to diverge, you're too close to the eye and you must pull away. Vertical height is controlled by joystick rotation.

Sometimes the reading will appear enclosed in parentheses, and this means the machine thinks it's somewhat suspect. In this case, you should repeat the reading to try and get a number without parentheses. Don't puff anyone more than three times per eye though! Occasionally, the intra-ocular pressure (IOP) will be over 30mmHg in which case you have to set the range button to the 30-60 setting.