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Schild et al. (129) compared IOP measurements with the Perkins applanation tonometer to measurements taken with the iCare rebound tonometer. They performed measurements with both instruments in 73 glaucoma patients in a supine position. The measurements of the iCare tonometer tended to be higher compared to the measurements taken by the Perkins applanation tonometer (2.6 ± 4.0 mmHg). The measurements of both instruments were in a range of ± 3 mmHg in 69% of the cases. The agreement of both instruments was best in IOPs between 16 and 23 mmHg. However in lower and higher IOPs the agreement was worse. In single cases the difference between both instruments was more than 10 mmHg.
Based on the results of the study the IOP measurements taken by both instruments are not exchangeable. As in the study the real IOP was not known it is impossible to judge which instrument measures the IOP more accurately. For the iCare tonometer to obtain a measurement in a supine body position, the head of the patient needs to be tilted to the side. However, recently the same manufacturer introduced the iCare Pro tonometer. With this instrument a tilting of the head is not necessary. Probably this new instrument will show different results and a better agreement with the Perkins applanation tonometer.