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First Author: W.Halim MALAYSIA
Co Author(s): M. Rana S. Naroo M. Nessim S. Shah
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To study the test-retest reliability of Corvis ST measurements of the IOP, pachymetry and corneal biomechanic indices.
The outpatient clinic of the Birmingham and Midland Eye Centre, United Kingdom.
This is a cross sectional study with a total number of 335 eyes from 179 patients. Patients underwent 3 repeated measurements with Corvis ST by a single operator. All the measurements were taken within 5 minutes duration, with less than one minute gap in between measurements. Each measurement yield IOP, central corneal thickness (CCT) and corneal biomechanic indices. The corneal movement indices are applanation 1 time (A1T), applanation 1 lentgh (A1L), applanation 1 velocity (A1V), applanation 2 time (A2T), applanation 2 length (A2L), applanation 2 velocity (A2V), highest concavity time (HCT), highest concavity radius(HCR), highest concavity peak distance (HCpD) and highest concavity deformation amplitude (HCdA). Repeatability and reproducibility were assessed by the intraclass correlation coefficient (ICC) with confidence interval (CI) set at 95%.
The intraoperator repeatability for IOP measurements is high with ICC 0.91, with 95% CI (0.84, 0.92). The ICC for the CCT measurement is 0.98 with 95% CI (0.97, 0.99). The corneal movement indices that showed high repeatability are A1T (ICC=0.911), A2T (ICC=0.87), A1V (ICC=0.76), A2V (0.76), HCpD (ICC= 0.68), HCR (ICC= 0.87) and HCdA (ICC= 0.92). Whilst, for A1L, A2L and HCT, the value of the ICC are 0.28, 0.34 and 0.31 respectively.
Corvis St is a reliable instrument for tonometry and pachymetry. However, this is not reflected in the overall corneal movement indices measurements.