Tonographic Effect, Inter- and Intra-observer Variability of Three Tonometers (goldmann, Ora, Dct)

Abstract

Purpose: : To evaluate the tonographic (tng) effect and to compare the inter/intra-observer variability (vrbl) of IOP measures of 3 tonometers: GAT , DCT and ORA

Methods: : The tonographic effect was evaluated in 25 subjects after 1 minute (min) and in 28 after 2 min. Measures were repeated 1 min apart in 3 groups of subjects using the three different methods (GAT: 20 subjects, ORA: 35 subjects, DCT: 27 subjects). IOP was measured with GAT, DCT and ORA in 152 POAG, in a randomized order, by 2 independent observers. One measure per tonometer was taken one min apart from the others. Five min rest was allowed between each set of measures. Corneal thickness was measured in all the subjects. One random eye was considered for analysis.

Results: : No significant tonographic effect was evident after one and two min single measure. When considering 10 repeated measures for each tonometer IOP was significantly reduced from the 4^th measure with GAT (t: 2,5; p: 0,01) and DCT (t: 3,5; p: 0,001), and from the 8^th with ORA (t: 2; p: 0,04). Mean intra-observer variability was 0,6 mmHg for GAT, -0,2 mmHg for ORA and 0,5 mmHg for DCT. Mean inter-observer variability for GAT was 0,5 mmHg; for ORA 0,7 mmHg and for DCT 0,2 mmHg. A small but significant correlation could be demonstrated when IOPg measures where correlated with CCT. IOP measures with ORA and DCT were higher than with GAT.

Conclusions: : A tonographic effect could be demonstrated after repeated measurements and was more pronounced with the contact tonometers (GAT, DCT). This observation should be taken into account when performing multiple inter and intra-observer measures. ORA had the higher inter and intra-observer variability.

Keywords: clinical (human) or epidemiologic studies: systems/equipment/techniques