Principles of non contact tonometry
Tonometry is a process that helps the eye care professional to measure the pressure of the eyes. This intra ocular pressure is the pressure of fluid inside the eyes. Tonometry forms a significant test in detecting patients to check their risk of suffering from glaucoma. The mechanism of almost all the tonometers shows the calibration in mm of mercury, denoted by “mm of Hg”.
Non contact tonometer isn’t the same as pneumatonometer. The non contact tonometer is better known as air puff tonometer. Bernard Grolman from Reichert, Inc had invented the non contact tonometer. The procedure requires a fast air pulse for applanation or flattening of cornea. Electro optical procedure is used for detecting the flattening of cornea. The ocular pressure of a patient is determined by recording force of this jet of air when the applanation of cornea is in process.
In the past, the non contact tonometers weren’t held as reliable sources. Rather they were used as simple and quick devices tomeasure the ocular pressure just preparing to go for a higher screening. It has been proved that non contact tonometer that is modern correlates quite well with the measurements taken through Goldmann tonometry. The tonometers that work without contact are a helpful device in that they can used for detecting the ocular conditions of children also of those who are non compliant.
The ORA or the Ocular Response Analyzer is a kind of non contact tonometer. It works on the basis of air puff and so dispenses with the employment of tropical anesthesia. You will get additional information about cornea and its biomechanical properties. The tonometer makes use of air pulse for deforming cornea into a slight concave shape. Difference in ocular pressures measured on the inward flattening of cornea and its outward flattening is measured with this tonometer. This process is termed as corneal hysteresis. The value is used by this machine to rectify the effect of cornea on the measurement.
The process of tonometry that doesn’t need contact employing OCT or Optical Coherence Tomography is undergoing development. Just like other forms that tonometry has, this method works by recording the corneal reaction as some force is applied on cornea. In matters of such non contact tonometer where OCT is used the force that is applied to cornea is measured with the help of the jets of air with high pressure, an acoustic or shock wave. The technique also consists of air at low pressure forced through the sealed chamber occurring around the eyes. Changes in curvature of cornea are measured by this device. It is also used to study the movements of corneal interfac at the apex with respect to the posterior interfaces like the retina. Recording difference between movements of the two interfaces gives an indication of how much the globe is compressed. The similarity between the movements of the two interfaces suggests globe retropulsion.
The non contact tonometer of the present day is not only reliable but it is acceptable to all.