| Measurement of intraoclar pressure (IOP) plays an important role in the clinical job of ophthalmology, especially in the diagnosis, monitoring, and management on glaucoma. It had been generally acknowledged that Goldmann applanation tonometry (GAT) is the most commonly used indirect method for identifying IOP and the gold standard for IOP measurement. However, the accuracy of GAT depends on many factors such as corneal thickness, corneal curvature, corneal rigidity, and astigmatism. There had some studies showed that GAT may overestimate IOP in eyes with thicker corneas and underestimate IOP in thinner corneas, these frequently lead to misdiagnosis and missed diagnosis in clinic.The new PASCAL dynamic contour tonometry (DCT), a third-generation digital contact tonometer supplied by SMT AG (Swiss Microtechnology AG, Ziemer Ophthalmic Systems Group Co, Port, Switzerland), adopted contour matching and pressure sensor principles to measure IOP. The DCT device features a cylindrical tip with a concave, contour-matched contact surface, thereby coming as close as possible to the shape which the cornea assumes if pressure within and outside the globe are identical and if no forces are acting perpendicularly on the cornea. When this "contour match" is reached, IOP can be measured by an integrated pressure sensor, thereby eliminating corneal rigidity and adhesion forces. Previous studies have shown that IOP measurements using DCT might be less affected by central cornea thickness (CCT). There had few studies about the application using DCT in extensive populations in our country, and the comparison of IOP measurement between GAT and DCT was important to indicate whether the DCT would replace GAT in future. The purpose of this study was to compare the differences of IOP measurement between GAT and DCT in extensive people, emphasis to establish the effects of CCT on IOP measured with GAT and DCT, then to assess the agreement and interchangeablity of IOP values obtained by DCT and GAT with different CCT in non-glaucomatous eyes. These would supply evidence for DCT replace GAT in the future.Objectives:1. Compare the differences of IOP measurement between PASCAL DCT and GAT.2. To investigate the agreement in the measurement of IOP obtained by DCT and GAT or correct GAT in non-glaucomatous eyes with different CCT, and analysis the impact of CCT on the differences of IOP values.3. To compare the IOP and OPA values obtained by DCT between right and left eyes.Methods:1. In a randomized order, two or three consecutive IOP measurements were performed on 487 eyes of 247 subjects by one examiner using both DCT and GAT on all eyes. Right eyes measured first, left eyes second, paired-t test was determined to compare IOP readings between DCT and GAT, rights eyes and left eyes were analyzed respectively.2. Bland-Altman analysis was used to evaluate agreement between the instruments on 293 eyes of 147 subjects which non-glaucomatous cases. The effect of CCT on GAT/DCT IOP differences was assessed by linear regression analysis, the Spearman correlation coefficient was determined to compare IOP readings between DCT and GAT in different CCT.3. Paired-t test were used to compare the DCT/IOP and OPA differences between right and left eyes.Results:1. Mean IOP values obtained by DCT in right and left eyes were (18.2±4.0/17.3±3.3)mmHg and GAT was (16.8±4.9/16.2±3.8)mmHg, the mean difference were 1.4/1.0mmHg in right and left eyes respectively.2. The 95% limits of agreement were wide in different CCT range. Mean difference (95% limits of agreement) between GAT and DCT was -1.6(-6.5 to 3.3) mmHg in right eyes and -1.1(-5.8 to 3.6) mmHg in left eyes.3. The IOP values had no significant difference between two instruments in thicker CCT group, and the difference had no correlation with CCT. In thinner and normal CCT groups, the IOP differences obtained by GAT and DCT both showed a significant correlation with CCT.4. Excluding the impact of CCT on the difference of instruments, mean difference (95% limits of agreement) between correct GAT and DCT was -0.3(-4.3to 3.7)mmHg in right eyes and -0.4(-4.6 to 3.8)mmHg in left eyes.5. In non-glaucomatous cases, both DCT and OPA values were higher in right eyes than that in left eyes (t=2.399, P= 0.018/t= 3.49, P=0.001), while the GAT IOP values had no difference between right and left eyes.6. OPA values showed a weak correlation with DCT IOP values both in right eyes and left eyes(r= 0.259, P=0.002/r=0.262, P=0.002).Conclusions:1. PASCAL DCT and GAT revealed a strong correlation in IOP measurements in extensively population.2. DCT and GAT IOP values had a strong correlation in different CCT, while the analysis of agreement indicated a wide range of the two instruments, the IOP values obtained by the two instruments could not be interchanged simple in clinic. In certain CCT range, the corrected GAT/IOP values could interchange with DCT/IOP values.3. Both IOP and OPA values obtained by DCT showed significant differences between right and left eyes, and OPA had a weak correlation with IOP. |
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