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M.-M. Cayer, J. Wang, M. Chagnon, M. R. Lesk; Assessment of Factors Affecting the Difference in Intraocular Pressure Measurements Between Dynamic Contour Tonometry and Goldmann Applanation Tonometry. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2861.
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To determine if the difference in intraocular pressure (IOP) measurements between dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) is correlated to axial length (AL), and to assess the possible influence of age, sex, central corneal thickness (CCT), corneal hysteresis (CH) and glaucoma status on the difference in IOP measurements between the two instruments (ΔIOP = DCTIOP- GATIOP).
247 subjects (480 eyes) in the following 4 groups were included in this cross-sectional study: 41 healthy subjects (80 eyes), 105 glaucoma patients (200 eyes), 49 glaucoma suspects (96 eyes) and 52 patients with ocular hypertension (104 eyes). Subjects underwent IOP evaluation with DCT and GAT as well as AL, CCT and CH measurements. The level of correlation between AL and ΔIOP was determined. The influence of age, sex, CCT, CH and glaucoma status on the difference in IOP measurements between the two instruments was also evaluated. Right and left eyes were analyzed separately.
The IOP difference between DCT and GAT was higher in eyes with longer axial lengths in both right eyes (r = 0.138; p = 0.034) and left eyes (r = 0.239; p = 0.000). Per paired t test, ΔIOP was statistically higher in male subjects (p = 0.020) in left eyes only. A correlation between ΔIOP and CH was found in left eyes (r = -0.163; p = 0.011), where the ΔIOP increased as CH decreased (corresponding to more viscoelastic corneas). Such a correlation was not found in right eyes (r = -0.009; p = 0.886). An analysis of variance (ANOVA) showed that glaucoma status had a statistically significant influence on ΔIOP in left eyes (p = 0.010), with greater underestimation of IOP by GAT relative to DCT in glaucoma patients. The ΔIOP was found to be the lowest in the ocular hypertensive group. No effect of age and CCT on the ΔIOP was found.
The level of underestimation of IOP by GAT relative to DCT is not constant between patients. This study shows that the difference in IOP measurements can be influenced by different factors, the most significant being AL. As AL increases, the underestimation of IOP by GAT relative to DCT tends to increase. Other factors that were shown to be significant were sex, CH, and glaucoma status, although these were significant in left eyes only.
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