Goldmann-Applanationstonometrie und dynamische Konturtonometrie

Goldmann Applanation Tonometry Versus Dynamic Contour Tonometry After Vitrectomy

PURPOSE

The aim of the study was to investigate the agreement of intraocular pressure (IOP) measurement using dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in eyes after vitrectomy with intraocular gas endotamponade, in eyes after vitrectomy with no tamponade, and in controls.

METHODS

In this prospective comparative study IOP was measured with GAT and DCT in 41 eyes with gas endotamponade (sulfur hexafluoride 20%) 1 to 3 days after vitrectomy, in 32 postvitrectomy eyes with intraocular water, and in 46 control eyes with no history of glaucoma or intraocular surgery. Corneal pachymetry and axial length measurements were additionally performed.

RESULTS

The mean difference between GAT and DCT (GAT-DCT) in gas-filled eyes was 3.1 mm Hg [SD=6.2 mm Hg], that in eyes after vitrectomy with no tamponade was 0.4 mm Hg (SD=4.8 mm Hg), and in control eyes was 0.4 mm Hg (SD=3.8 mm Hg). No significant correlation was found between the differences of GAT and DCT (GAT-DCT) and the mean IOP of GAT and DCT in water-filled eyes (r=-0.25, P=0.18) and control eyes (r=0.23, P=0.13), but a significant correlation was found in the gas-filled eyes (r=0.71, P<0.0001). A significant correlation between central corneal thickness and the mean difference of both methods was seen only in the control group (r=0.36, P=0.03).

CONCLUSIONS

IOP as determined by DCT underestimates IOP in gas-filled eyes compared with GAT, as GAT values were on average 3.1 mm Hg higher compared with those of DCT. The extent of IOP underestimation using DCT increases with higher IOP values. In the group of eyes after vitrectomy and in normal eyes we found a generally good agreement between the 2 methods, although high interindividual discrepancies were present. Our findings suggest that the 2 devices should not be used interchangeably in IOP evaluation after vitrectomy with gas endotamponade, which remains a difficult challenge.

Comparison of dynamic contour tonometry and Goldmann applanation tonometry in keratoconus

PURPOSE

We performed a comparative study using Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) to measure intraocular pressure (IOP) in eyes with keratoconus.

METHODS

IOP was measured in 114 eyes of 75 patients with keratoconus (51 men and 24 women; mean age, 36.1 ± 11.2 years) using GAT and DCT in randomized order. Central corneal thickness (CCT), minimal corneal thickness (MCT), and corneal topography were recorded using the Pentacam. Four groups according to Amsler's keratoconus classification were composed and analyzed for significant differences of CCT, MCT, GAT, and DCT results.

RESULTS

Mean CCT in the 114 keratoconus eyes was 481.1 ± 46.2 μm (range, 334-601 μm). Mean MCT was 453.3 ± 56.3 μm (range, 239-573 μm). Mean IOP measured using GAT was 13.1 ± 2.9 mm Hg, whereas mean IOP measured using DCT was 14.8 ± 2.6 mm Hg. Neither the results for GAT nor those for DCT showed a significant correlation with CCT (Pearson correlation: P < 0.05). Multifactorial analysis revealed that CCT and MCT, but not GAT and DCT, results were significantly different in corneas of varying curvatures.

CONCLUSIONS

This study shows that DCT measures IOP higher than GAT in eyes with keratoconus. In keratoconus, both methods seem to be independent of CCT and therefore are equally, but not interchangeably, applicable when monitoring IOP. Further analysis revealed that CCT and MCT are significantly different in corneas of varying Amsler grade.

Pascal, ICare and Goldmann applanation tonometry--a comparative study

PURPOSE

To compare intraocular pressure (IOP) measurements by Pascal, ICare and Goldmann applanation tonometry (GAT), to evaluate the effects of central corneal thickness (CCT) and curvature on IOP measurement and to estimate the intra-observer variability.

METHODS

A prospective, single-centre study of 150 eyes with a wide range of pressures. Six masked IOP measurements/method; corneal thickness and curvature were studied for each eye. GAT was the reference.

RESULTS

IOPPascal and IOPICare correlated with IOPGAT (r = 0.91, 0.89). Mean ICare measurement exceeded GAT by 2 mmHg. Pascal measured higher than GAT at low IOPs and lower at high IOPs. For every 10 mmHg increase in IOP above 31 mmHg, Pascal measured 2 mmHg lower than GAT and vice versa. CCT was correlated significantly with IOPGAT (r = 0.23) and IOPICare (r = 0.43) but not with IOPPascal (P = 0.12). CCT was correlated with age. In a subgroup (>50 years), ICare and the difference between IOPGAT and IOPPascal were affected significantly by the CCT, whereas IOPGAT and IOPPascal were not. Corneal curvature was correlated significantly with IOPGAT (r = -0.27) and IOPPascal (r = -0.26) but not with IOPICare (P = 0.60). Intra-observer variability within each set of six measurements was approximately 2 mmHg, irrespective of method.

CONCLUSION

This study showed a reasonable overall correlation and concordance between the IOP obtained with the three instruments. None of the methods were completely independent of the biomechanical properties of the cornea. ICare showed a significant dependency upon CCT, whereas GAT and Pascal showed a significant dependency on corneal curvature. All methods showed intra-observer variability, which leaves room for further improvement of methods.

Evaluierung der Reboundtonometrie (ICare) im Vergleich zum TonopenXL und dem Goldmann-Applanationstonometer

BACKGROUND

Goldmann applanation tonometry and dynamic contour tonometry (PASCAL) are two well established slit lamp mounted tonometric methods. Intraocular pressure measurement in bedridden patients and children is often only possible using hand held tonometers (TonoPenXL, Perkins tonometer, Draeger tonometer). This study was performed to evaluate the hand held ICare tonometer, which is based on the rebound method.

METHODS

A total of 102 eyes were examined by two highly experienced ophthalmologists for: 1) ophthalmological status, 2) central corneal power (Zeiss IOL-Master), 3) central corneal thickness (Tomey ultrasound pachymetry, five successive measurements, SD<5%), 4) intraocular pressure (IOP) measurement with the Goldmann applantation tonometer (GAT) 1x, 5) TonoPenXL (1x), 6) ICare with three successive measurement series of 6 single measurements.

RESULTS

The mean IOP(GAT) was 13.2+/-3.0 mmHg compared with the mean IOP(TonoPenXL) (13.4+/-3.1 mmHg) and with the IOP(ICare) (mean value of first measurement series: 13.4+/-3.1 mmHg). The series of measurements with the ICare showed a tonography effect (decrease of IOP from 14.6 mmHg at the first measurement and 14.2 mmHg at the second to 14.0 at the third measurement). The ICare-measurements were highly reliable (Cronbach's alpha=0.974) and showed a good correlation between the measurement series (r=0.592-0.642; p<0.001). There was a great intra-individual variability of up to 17 mmHg between the GAT, TonoPenXL and ICare methods.

CONCLUSIONS

The ICare tonometer is easy to handle and high reliability. The data are comparable with those from the Goldmann tonometer. A tonography effect of 0.6 mmHg in the successive measurement series was found.

[Dynamic contour tonometry]

Dynamic contour tonometry (DCT) is a new technology for noninvasive and direct measurement of intraocular pressure (IOP); its results are thought to be influenced less than those of other methods by structural characteristics of the eye. The curvature of the pressure sensing device is concave and only slightly flatter than that of the human cornea. The cornea adapts to the curvature of the transducer head, and the sensor in the centre of the adapted area measures the pressure on the other side of the cornea in the force-free range. Studies published so far suggest that DCT is less heavily dependent than applanation tonometry on the biomechanical properties of the cornea . A further advantage of DCT over other forms of tonometry is the capability of dynamic measurements over time. It is also possible to measure both the diastolic and the systolic IOD and determine the difference between the two, i.e. the ocular pulse amplitude (OPA). OPA is an indirect indicator of choroidal perfusion and reflects the condition of the arterial vascular system and the action of the heart. It could be important in the diagnosis and treatment of glaucoma.