Purpose: To determine the prevalence of calibration errors in Goldmann applanation tonometers at Farabi Eye Hospital.Methods: This cross-sectional study was performed on all tonometers in use at Farabi Eye Hospital. All Haag-Streit Goldmann applanation tonometers were checked according to the manufacturer’s method by two independent observers and by a third observer in case of mismatched results. Calibration errors were classified into 6 categories of ±0.5, ±1, ±1.5, ±2, ±2.5 and more than ±2.5 mmHg. Results: Overall, 43 Goldmann tonometers were evaluated. There were 3 (7%), 10 (24.3%), 16 (38.3%), 24 (56.9%), 31 (72.1%) and 12 (27.9%) tonometers within calibration errors of ±0.5, ±1, ±1.5, ±2, ±2.5 and more than ±2.5 mmHg respectively.Conclusion: Goldmann tonometers were not within the manufacturer's recommended range (±0.5 mmHg) in 93%, and not within the acceptable range of ±2.5 mmHg in 28% of checked devices. Further study is needed to demonstrate the correlation between calibration errors and clinical errors.

Purpose: To evaluate intraocular pressure (IOP) changes measured by Goldmann applanation tonometry (GAT) after laser in situ keratomileusis (LASIK). Method: In 60 patients (120 eyes), IOP was measured with GAT in the central cornea, before and 1 week, 1 month, and 3 months after LASIK and was compared with one way ANOVA Test. Correlation of refractive errors, keratometry, ablation depth, and IOP changes were evaluated. Results: Pre-operatively, mean IOP (SD) was 16.48 (2.16) mmHg, that reached 13.78 (2.6), 13.93 (2.16), and 13.83 (2.55) at one week, one month, and 3 months after LASIK, respectively. We observed a mean IOP (SD) decrease of 2.5 (2.54) mmHg, 2.7 (2.6), and 2.65 (2.5) at one week, one month, and 3 months after LASIK, respectively (P<0.001). Mean (SD) preoperative pachymetry was 542.9 (34.78) mm; postoperatively (3 months) was 470.66 (45.2) mm; mean (SD) ablation depth was 74.18 (34.7). There was significant correlation between IOP and ablation depth (P=0.002, regression analysis test). No significant correlation was found between decrease in IOP and change in spherical equivalent, age, sex, or keratometry. Conclusion: Overall, IOP decreased after LASIK by 1.9-3.8 mmHg. The cause of this reduction is unknown. Central corneal thickness is an important variable in applanation tonometry and should be considered in the assessment of any case of potential glaucoma or ocular hypertension. Therefore, in patients who have undegone LASIK some underestimation of IOP measurements can occur which has implications in undetected glaucomatous damage.

Purpose: To investigate the correlation between central corneal thickness (CCT) and intraocular pressure (IOP) measured by Schiotz and Goldmann tonometers.Methods: CCT and IOP were determined by ultrasonic pachymetry and with the Goldmann and Schiotz tonometers, respectively. The correlation between IOP measured by Goldmann and Schiotz tonometers on one hand and CCT on the other was determined by regression analysis.Results: Overall, 168 eyes of 168 glaucoma patients including 85 male (50.6%) and 83 female (49.4%) subjects with mean age of 54.6±19.8 (range 7-85) years were evaluated. Mean CCT was 547.6±53.02 (range: 446-848) mm without any significant difference between men and women (P=0.811). IOP was correlated with CCT with both types of tonometry: every 20 mm change in CCT was associated with 1.9±1.4 mmHg and 1.54±0.95 mmHg change in IOP as measured by the Goldmann and Schiotz tonometers respectively with no statistically significant difference between the two devices (P=0.6). Conclusion: IOP measurement by Schiotz tonometry is affected by CCT to the same extent as Goldmann applanation tonometry.

Purpose: The dynamic contour tonometer (DCT) is a novel tonometer designed to measure lOP independent of corneal properties. The purpose of this study is a comparisonof lOP measured with the DCT and the Goldmann applanation tonometry (GAT), before and after keratorefractive surgery.Materials & Methods: In a cross-sectional study of 154 myopic and myopic astigmatism eyes, central corneal thickness (CCT) was measured ultrasonically and lOP measured before and 1 month after LASIK and PRK with DCT and GAT. The correlation between these two methods with each other and eachone with CCT analyzed with linear regression and Pearson Correlation.Results: Mean lOP before surgery with GAT was 17.85±2.64mmHg and after surgery was 13.56±2.64mmHg. Mean lOP before surgery with DCT was 18.79±3.5mmHg and after surgery was 17.39±3.5mm Hg. Corneal ablation of 90.4±5 Micron, reduced lOP readings by GAT and DCT, but this Reduction was significant in GAT in comparison with DCT (P<0.0001).Conclusion: CCT and corneal rigidity causes an error in tonometery. DCT can measure real lOP reading and independent from corneal properties. This study revealed that the lOP measurement with DCT has no Correlation with CCT. (Pearson correlation r=-0.4 and p=0.5).

Purpose: To compare intraocular pressure (IOP) readings measured by the Ocular Response Analyzer (ORA) with those measured by the Goldmann applanation tonometer (GAT) in keratoconic eyes following penetrating keratoplasty (PKP) and to evaluate the influence of anatomical and biomechanical properties of the grafts on IOP measurements.Methods: This cross-sectional study was conducted on 45 keratoconic eyes undergoing PKP. IOP was measured using the GAT (IOP GAT); corneal hysteresis (CH), corneal resistance factor (CRF), Goldmannrelated IOP (IOPg), and cornea-compensated IOP (IOPcc) were obtained using the ORA; central graft thickness (CGT) was measured by ultrasonic pachymetry. Bland-Altman and mountain plots were used to evaluate agreement between the tonometers. The correlation of graft curvature and astigmatism; central graft thickness (CGT); and corneal biomechanical properties with IOP readings was investigated using multivariate regression analysis.Results: Mean patient age was 29.8±6.1 years and mean follow up was 91.2±35.4 months. Mean CH, CRF, and CGT were 10.2±2.1 mmHg, 10.1±2.2 mmHg, and 565.4±37.7 mm, respectively. Mean IOP GAT, IOPg, and IOPcc were 12.2±2.4, 15.1±3.5, and 15.8±3.3 mmHg, respectively (P<0.001). The 95% limit of agreement between IOP GAT and IOPg ranged from -3.6 to 9.3 mmHg. CH and CRF, but not CGT or keratometric astigmatism was significantly associated with IOP GAT, IOPg, and IOPcc.Conclusion: Graft biomechanics had more influence on IOP values as compared to anatomical features. In comparison to GAT, the ORA seem to overestimate IOP in post-PKP eyes.