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Understand the Pressure
Evidence in ophthalmic literature continues to mount, leading experts to question whether the Goldmann tonometer is sensitive and specific enough to be used for the critical purpose of measuring IOP in the diagnosis and management of Glaucoma.
The Goldmann tonometer is designed to provide accurate measurements in eyes having average central corneal thickness (CCT). Corneal thickness, though, varies significantly more than previously thought. Furthermore, it is now known that the material properties of the cornea have an even greater influence on tonometry results than CCT alone. The Ocular Response Analyzer measures these complex tissue parameters, providing a pressure measurement (IOPCC) that is less influenced by corneal properties.
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“Assuming that CCT can be used as a correction factor for GAT is a misinterpretation of the results of OHTS… that couldn’t be further from the truth. Adjusting IOP based on CCT is attempting to instill a degree of precision into a flawed meaurement. You may actually correct in the wrong direction. The issues related to the most accurate tonometry need to include the material properties of the cornea”
James Brandt, MD, Director, Glaucoma Services, UC Davis
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Since IOPCC compensates for corneal influence, it facilitates post-LASIK pressure measurements that are not artificially lower than pre-LASIK values. Goldmann-measured IOP values are known to drop 2-6 mmHg, or more, post LASIK. IOPCC values for a population of 14 eyes pre and post LASIK exhibit an average post-LASIK IOPCC reduction of less than 1 mmHg.
In addition, some investigators believe that Goldmann tonometry underestimates the true pressure in “Normal Tension Glaucoma” eyes. In a population of 24 NTG eyes, IOPCC is more than 2.25 mmHg higher, on average, than the Ocular Response Analyzers' Goldmann correlated IOP measurement (IOPG); a significant difference when diagnosing and managing glaucoma.
IOPCC and IOPG in 24 NTG eyes
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