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Accuracy of Reichert Ophthalmic Instruments

Submitted by Agnes on Sun, 10/11/2009 - 1:01pm

Non-contact Tonometer or Air-puff Tonometer (Reichert Ophthalmic Instruments, Depew, New York, USA)

Grolman created this non-contact applanation tonometer in the 1950s aiming to make it available for optometrists to perform tonometry measurements. Briefly, an air-puff causes a transient applanation of the cornea, while an infrared light beam is reflected by the flattened surface. The amount of light reflected during the applanation period is compared with the time the air-puff took to cause applanation, allowing this device to provide an electronic measurement of the IOP. It also provides the ocular pulse amplitude and tonographic measurements that estimate the aqueous outflow efficiency of the trabecular meshwork according to manufacturer information. Historically, non-contact tonometers were not considered to be the most accurate way to measure IOP. There were concerns that low pressures were overestimated and high pressures underestimated. The oldest versions of this tonometer showed a fair agreement with GAT (±3 mmHg), but tended to overestimate the IOP for pressures lower than 10 mmHg and underestimate it for values above 19 mmHg.50 However, modern non-contact tonometers correlate very well with GAT IOP, even though they tend to systematically overestimate it by between 0.12–0.58 mmHg.51-53 With regard to the influence of corneal properties on noncontact tonometry measurements, it is likely that they are more influenced by CCT than GAT. In thinner corneas, there seems to better correlation between the tonometers, while in thicker corneas, non-contact tonometry systematically yields higher readings than GAT.54

In summary, non-contact tonometers have generally been considered a fast and simple way to screen IOP. The benefits of non-contact tonometry include patient preference, less operator dependence, and no risk of infection transmission.50-53

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