Contact Tonometry

Tonometry is the measurement of tension or pressure within the eye. It is advisable for adults, particularly individuals over 40 to have their intraocular pressure (IOP) measured routinely as elevated IOP’s can lead to optic nerve damage. The optic nerve is a crucial part of the visual system; it collects all the visual information gathered by the photoreceptors of the retina and transmits this information to the brain, where the signals are interpreted as vision. Optic nerve damage can lead to decreased peripheral vision (tunnel vision) and loss of nerve tissues. Elevated IOP’s can commonly occur without symptoms, meaning like many other eye conditions the individual may be unaware there is a problem. Elevated IOP’s is associated with Glaucoma; as a result tonometry is important in diagnosing and monitoring Glaucoma.

Applanation tonometry involves the use of an eye drop containing a local anesthetic and a yellow dye called fluorescein which the optometrist will instill prior to measuring IOP’s. A Goldmann tonometer (gold standard for IOP measurement) is then attached to the optometrists slit lamp microscope and using a special cobalt blue light the optometrist is able to accurately measure IOP’s in millimeters of mercury (mmHG). In normal individuals the pressure is commonly between 10-21mmHg. In individuals with elevated IOP’s the measurements will be repeated on a separate day at a different time of day to account for fluctuations in IOP at different times of day. The procedure is completely painless, takes only a few seconds to perform and shouldn’t affect your vision meaning driving afterwards is safe.

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