Abstract
Abstract: :
Purpose:To compare dynamic contour tonometry with Goldman applanation tonometry for the assessment of intraocular pressure in structurally normal thick and thin corneas. Methods: 25 patients each with normal corneal thickness (CCT=520–580µm:group A), thin corneas (CCT<520µm: group B) and thick corneas (CCT>580µm: group C) had two measurements each of intraocular pressure (IOP) using both the dynamic contour tonometer (DCT) and the Goldman applanation tonometer(GAT). Patients with corneal disease, a history of corneal surgery or more than 3 dioptres of astigmatism were excluded. One eye per patient was randomly selected for analysis. Corneal thickness was measured using ultrasound pachymetry.The relationship of the GAT–DCT difference to CCT was examined. Results: In group A (mean CCT=552±16µm) the mean GAT was 15.9±3.1mmHg and mean DCT was 16±3.3mmHg (p=0.91). In group B (mean CCT= 491±19µm) the mean GAT was 13.2±3.5mmHg, significantly lower than the mean DCT of 15.9±3.5mmHg (p=0.009). For group C (mean CCT=615±22µm), the mean GAT was 17.4±3.8mmHg and the mean DCT was 17.4±3.5mmHg (p=0.95). There was no tendency in group C for either instrument to measure consistently higher or lower that the other. The 95% agreement limits for DCT with GAT, based on data from patients with normal CCT, were –3.1mmHg to +2.9mmHg. The mean GAT–DCT difference was –2.6±1.9mmHg in thin corneas and –0.06±2.6mmHg in thick corneas. Below 520µm, a reduction of 10µm in CCT appears to result in a significant underestimation of the IOP using GAT, by 0.7mmHg relative to DCT (p<.001) and above 580µm there appears to be a non–significant overestimation of 0.2mmHg per 10µm increase in CCT using the GAT relative to the DCT (p=0.27). Conclusions: DCT agrees well on average with GAT but the agreement limits are wide. In structurally normal thin corneas DCT may give a more accurate assessment of the true IOP, and appears to correlate well with suggested conversion factors for corneal thickness based on previous manometric experiments. However it does not appear to have any benefit over GAT in thick corneas.
Keywords: intraocular pressure • clinical (human) or epidemiologic studies: systems/equipment/techniques