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Are disposable prisms an adequate alternative to standard Goldmann tonometry prisms in glaucoma patients?

Maino AP, Morgan LH, Hercules BL, Tullo AB

Royal Eye Hospital, Manchester, United Kingdom. a.maino@doctors.net.uk

PURPOSE: To evaluate the accuracy and reliability of 2 single-use tonometry devices (Tonosafe and Tonojet) as an alternative to standard Goldmann prisms in patients attending dedicated glaucoma clinics. DESIGN: Prospective experimental study with human subjects. PARTICIPANTS: Two hundred forty glaucoma patients who attended 2 glaucoma clinics at the Stepping Hill Hospital between January and February 2005. METHODS: During each examination, intraocular pressure (IOP) was measured 3 times, using the standard Goldmann prism, Tonosafe, and Tonojet, respectively. The prism sequence was predetermined at random using a computer, and the measurements were taken at 5-minute intervals. Data were analyzed using the Bland-Altman method of differences. MAIN OUTCOME MEASURE: Intraocular pressure. RESULTS: Intraocular pressure ranged from 6 to 68 mmHg. Linear regression analysis indicated that there was a proportional bias between Goldmann and Tonosafe (r2 = 0.368, P<.001), especially for values higher than 25 mmHg. On the other hand, there was no statistically significant proportional bias between Goldmann and Tonojet (r2 = 0.006, P = 0.14). CONCLUSIONS: Caution should be exercised when using Tonosafe prisms in the presence of IOP higher than 25 mmHg. On the other hand, Tonojet is an adequate and useful alternative to the Goldman tonometer for glaucoma patients.

Published 2 October 2006 in Ophthalmology, 113(10): 1837-41.
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