Dynamic contour tonometry: handheld versus slit-lamp-mounted.Ophthalmology 2009; 116(8):1450-4O
To compare the newly developed handheld dynamic contour tonometer (hh-DCT) with the established slit-lamp-mounted DCT (sl-DCT) in terms of agreement for intraocular pressure (IOP) and ocular pulse amplitude (OPA) measurements, intraobserver variability, and tonography effect.
Evaluation of diagnostic technology.
Fifty eyes of 50 healthy volunteers were examined with the hh-DCT and sl-DCT.
A paired t test was performed to analyze differences in IOP and OPA readings. Measurements were compared for bias and agreement according to the method of Bland and Altman. Intraclass correlation coefficients (ICCs) were calculated to compare intraobserver variability. A mixed model analysis was performed to assess a possible tonography effect.
MAIN OUTCOME MEASURES
The differences in IOP and OPA measurements, intraobserver variability, and tonography effect between the hh-DCT and the sl-DCT were examined.
No statistically significant differences in IOP (sl-DCT-hh-DCT: 0.1+/-1.43 mmHg, 95% confidence interval [CI], -0.31 to 0.5, P = 0.63) or OPA (sl-DCT-hh-DCT: -0.1+/-0.52 mmHg, 95% CI, -0.28 to 0.01, P = 0.08) measurements were detected. Bland-Altman analysis revealed a bias of 0.1 with the limits of agreement of IOP measurement differences ranging from -2.71 to +2.90 mmHg. With regard to IOP readings obtained by sl-DCT, hh-DCT overestimated IOPs less than 15.6 mmHg and underestimated IOPs more than 15.6 mmHg. ICCs calculated for IOP readings were 0.87 (95% CI, 0.8-0.92) for hh-DCT and 0.85 (95% CI, 0.78-0.90) for sl-DCT. ICCs for OPA readings were 0.86 (95% CI, 0.79-0.91) for hh-DCT and 0.87 (95% CI, 0.8-0.91) for sl-DCT. Comparing the ICCs revealed no statistically significant difference between the devices with regard to IOP and OPA measurements (P = 0.53 and P = 0.93, respectively). Mixed model analysis of 3 consecutive IOP measurements revealed a decrease in IOP of 0.5 mmHg after each measurement in both devices, which was not significant between the 2 methods (P = 0.68).
IOP and OPA readings obtained by the novel hh-DCT were shown to be strongly concordant with measurements obtained by the sl-DCT device. The hh-DCT may be a valuable alternative to the sl-DCT in clinical practice.