The Different Methods Used To Measure Eye Pressure
Despite the advancement of methods in measuring intraocular pressure during the past couple of centuries, it is said that the famous Dr. Claus Dohlman, Harvard professor of Ophthalmology at the Massachusetts Eye and Ear Infirmary, remains as accurate in measuring IOP with his fingers as any ophthalmologist using the high-tech tonometers of today.
The most common method used to measure eye pressure is the Goldmann applanation tonometry. Goldmann’s applanation tonometer is neither the first method nor the most recent intraocular pressure measurement. With Goldmann tonometry, in 1950, the era of accurate intraocular pressure measurement began. Although firmness of the eye with glaucoma has been identified as far back as the 10th century, elevated intraocular pressure was not routinely assessed until the latter part of the 19th century. The first instrument for measuring intraocular pressure was developed in 1865 by Von Graefe. In the late 19th century, the first reasonably accurate instrument was the Maklakoff applanation tonometer, it was in widespread use throughout Eastern Europe until relatively recently.
The Goldmann applanation tonometry is the ‘gold standard’ for pressure testing. Among other methods, the goldmann tonometry is the most widely used in the world. A small device attached to the front arm of the slit lamp, emits blue light, and touches the tip of the cornea as the eye care professional measures the pressure by adjusting the tonometer drums and exerting a slight pressure forward with the slit amps joystick.
The first clinically useful mechanical tonometer was designed and introduced by Hjalmar Schiotz in the early 1900s. The instrument was simple, easy to use, and highly precise. The Schiötz tonometer was an indentation tonometer that became widely used throughout the world. A common glaucoma screening test is non-contact tonometry (NCT). NCT consists of an electronic instrument that emits a fast air puff at the surface of the eye to indirectly measure the pressure inside your eye.
Other devices such as the Mckay-Marg tonometer, Perkins hand-held, the pneumatonometer, and applanation tonometers have largely been used by many practitioners. The dynamic contour tonometer is the first totally new concept in tonometry in over 100 years. It is considered to be the most accurate and non-invasive of all the tonometers. It directly measures the pressure of the eye with precise results irrespective of the corneal thickness as well as the ocular pulse amplitude, a variable that has controversial significance in the diagnosis and management of glaucoma. It is based on the principle that when the tip of the device exactly matches the contour of the cornea, the pressure measured by a transducer placed on its tip is an accurate indicator of the true intraocular pressure. Further studies are required to determine the effectiveness of the dynamic contour tonometer in patients having an abnormal or irregular corneal contour.