Clinical evaluation of the Topcon CT10 tonometer

Effect of manual upper eyelid elevation on intraocular pressure measurement by noncontact tonometer

PURPOSE

To evaluate whether manual upper eyelid elevation (MUEE) affects intraocular pressure (IOP) values obtained with a noncontact tonometer (NT).

METHODS

This cross-sectional study included 122 eyes of 122 non-glaucomatous adults. All patients underwent IOP measurement using both NT and Goldmann applanation tonometer (GAT). The order of measurements was NT without MUEE, NT with MUEE, and GAT. Both eyes of each patient were measured and one of the eyes was randomly selected for inclusion in the study. Central corneal thickness (CCT) and palpebral fissure height (PFH; distance between upper and lower eyelids) was recorded.

RESULTS

The patients' mean age was 43.91 ± 12.36 (20-61) years and 62.3% were women. Mean IOP values measured by NT without MUEE, NT with MUEE, and GAT were 15.98 ± 2.39, 15.84 ± 2.53, and 14.33 ± 2.3 mmHg, respectively. There was no statistically significant difference in mean IOP between NT without and with MUEE (p = 0.506). Mean IOP values obtained by NT with and without MUEE were significantly higher than those obtained by GAT (p < 0.001). The difference in IOP values measured by NT without and with MUEE was positively correlated with PFH (r = 0.214; p = 0.018). CCT and IOP values obtained by NT without MUEE and GAT were positively correlated (r = 0.300; p = 0.001 and r = 0.311; p = 0.001, respectively).

CONCLUSION

MUEE does not have a significant effect on IOP measurements by NT. The difference between IOP measured by NT without and with MUEE increases with greater PFH.

Effect of central corneal thickness on intraocular pressure and comparison of Topcon CT-80 non-contact tonometry with Goldmann applanation tonometry

BACKGROUND

To compare intraocular pressure (IOP) measurements obtained with the Topcon CT-80 non-contact tonometer (NCT) and Goldmann applanation tonometer (GAT), in different ranges of IOP in normal and glaucoma subjects, and to assess the influence of central corneal thickness (CCT) on the IOP measurements in Asian Indian eyes.

METHODS

Four hundred and two eyes of 402 subjects (193 newly diagnosed primary open angle glaucoma [POAG] and 209 normal) were enrolled for this prospective study. For each eye, IOP was measured with GAT by a glaucoma specialist and NCT by a trained optometrist. The IOP values were compared among the tonometers in the three different IOP ranges (≤ 12 mmHg, 13-20 mmHg and ≥ 21 mmHg) using Bland-Altman graphs. Correlation between GAT and NCT was assessed by Pearson correlation co-efficient. CCT was measured with ultrasound pachymetry and its correlation with GAT and NCT was analysed using linear regression analysis.

RESULTS

The mean paired difference of IOP between NCT and GAT was 1.556 ± 2.69 mmHg (r = 0.26, p = 0.006) at IOP range of ≤ 12 mmHg, -1.665 ± 2.6 mmHg (r = 0.51, p < 0.0001) in IOP range of 13-20 mmHg and -2.202 ± 3.44 mmHg (r = 0.82, p < 0.0001) in the IOP range of ≥ 21 mmHg. Linear regression analysis showed a mean IOP variation of 0.27 mmHg per 10 μm change in CCT for NCT (p < 0.0001) and IOP change of 0.19 mmHg per 10 μm change in CCT for GAT (p = 0.01).

CONCLUSION

In this study of normotensive and POAG subjects, the Topcon CT-80 NCT showed an overestimation of IOP at the lower range and underestimation of IOP in normal and higher ranges of IOP. Clinicians should keep in mind that CCT influences IOP measurement with both types of tonometer and that the IOP readings obtained with these tonometers are not interchangeable.

A predictive model for postoperative intraocular pressure among patients undergoing laser in situ keratomileusis (LASIK)

PURPOSE

The aim of this study was to develop a predictive model based on preoperative variables for estimating postoperative intraocular pressure (IOP) of those eyes undergoing LASIK surgery, to predict the amount of underestimated IOP after LASIK for myopia and myopic astigmatism.

DESIGN

Pretest-post-test longitudinal study.

METHODS

Both eyes of 193 eligible subjects who underwent LASIK procedures at the Department of Ophthalmology, National Taiwan University Hospital, from July 2000 to December 2002 for myopia and myopic astigmatism were identified to build up the predictive models. IOPs were measured with noncontact air-puff tonometry. Information on age, gender, preoperative central corneal thickness (CCT), preoperative central corneal curvature (CCK), preoperative spherical equivalent refractive error, and ablation depth was collected and applied for predicting postoperative IOP after LASIK based on linear mixed model.

RESULTS

Significant predictors for postoperative IOP after myopic LASIK procedures included age, gender, preoperative IOP, ablation depth, preoperative CCT, and preoperative spherical equivalent refractive errors. The linear mixed model, taking into account these significant preoperative correlates and the correlation of IOPs between both eyes of the same patient, explained 91% of the variation of postoperative IOP.

CONCLUSIONS

A statistical model was developed for predicting the amount of underestimated IOP after LASIK for myopia and myopic astigmatism, which is of clinical importance to uncover ocular hypertension among patients whose information on postoperative IOP immediately after LASIK is not available.

Clinical evaluation of two non-contact tonometers

The precision and speed of two non-contact tonometers were examined and compared. The Goldmann applanation tonometer was used as the standard for precision. On the average the results obtained with the non-contact tonometers were not significantly different from those obtained with the Goldmann tonometer. The variation in the values obtained with the non-contact tonometers was greater. The speed of measurement differed between the two non-contact tonometers.