WHAT IS TONOMETRY TEST FOR GLAUCOMA?
In glaucoma, the intraocular pressure increases either because of blocked drainage or because of excessive production of aqueous humour. Applanation tonometry testing involves measurement of intraocular pressure using a tonometer, an instrument that is lightly pressed directly against the anaesthetized eye. The tonometry test can be conducted in any of three ways. In contact tonometry, in which the instrument touches the eye, the Schiøtz method, the Goldmann applanation method (commonly known as the “blue light” test), or a handheld method with a small pen–like tonometer may be used. Contact tonometers make an indentation in the eye with a specific amount of weight and record the amount of resistance to the indentation, which is then converted to intraocular pressure. In noncontact (indentation) tonometry, pneumotonometry or “air” tonometry may be used. Noncontact tonometry measures eye pressure indirectly. Noncontact tonometry has been found to improve compliance with testing in children, and there has been an improvement in the accuracy of the handheld units. However, noncontact tonometry results in the same client may be higher than the results from applanation tonometry. Pneumotonometry is the gentlest method and preferred for clients after LASIK surgery. The new dynamic contour tonometer is the most accurate. Overall, tonometry is superior to digital tension, which tends to underestimate pressure, for obtaining intraocular pressure in young children. The Goldmann applanation method is considered the criterion standard for this procedure.