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A. Kotecha, E. White, P. G. Schlottmann, D. F. Garway-Heath; Precision of IOP Measurements Made With the Goldmann Applanation Tonometer, the Dynamic Contour Tonometer and the Ocular Response Analyzer and Agreement Between Devices. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5219.
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Precision of GAT, DCT and ORA IOP measurements were assessed in 59 eyes of 59 subjects (from a planned total of 100) by 2 of 3 experienced observers. Three ‘good quality’ ORA measures were obtained in a fashion such that the observer was able to assess the raw ORA plot but remained masked to the IOP values. Two GAT and 3 DCT readings were made in a randomised order following the instillation of topical anaesthesia. GAT readings were obtained in a masked fashion, with one observer setting the dial to a random number and reading the final measurement. Only DCT readings of quality 2 or better were saved, and the first reading discarded as per the manufacturer’s instructions. The repeatability of IOP measures was calculated using 2.77 multiplied by the standard deviation of within subject differences in measurement. Device reproducibility and agreement was determined using Bland-Altman analysis.
The repeatability of GAT, DCT and ORA IOPcc measures for observer 1 was 2.5mmHg, 1.7 mmHg and 4.5 mmHg and for observers 2 and 3 (combined) was 2.3 mmHg, 2.0 mmHg and 4.1 mmHg, respectively. The mean difference in IOP measurements between observer 1 and observers 2 and 3 was: GAT 0.0 mmHg [ 95 % limits of agreement (LoA) -4.9 to 4.8]; DCT IOP -0.1 mmHg [95% LoA -4.2 to +4.0]; ORA IOPcc -0.3mmHg [ 95%LoA -7.3 to +6.7]. The mean difference between GAT and DCT measures was -2.0mmHg [ 95% LoA -6.0 to +2.1], GAT and ORA IOPcc was -1.9mmHg [ 95%LoA -7.3 to +3.6] and ORA IOPcc and DCT was -0.1mmHg [ 95% LoA -4.9 to +4.7].
The DCT gives a repeatable and reproducible measure of IOP and appears superior to GAT. The ORA IOPcc shows repeatability acceptable for a non-contact device, and shows slightly better agreement with the DCT than with GAT. IOP measures with both the DCT and ORA are higher than measures made with GAT.
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