Evaluation of a disposable prism for applanation tonometry

Background Recently the Medical Devices Agency recommended that 'ophthalmic devices that touch the surface of the eye should be restricted to single use'. Aim To evaluate one such device: a disposable tonometer prism for routine applanation tonometry. Methods The intraocular pressure (IOP) of 100 consecutive patients from a general eye clinic (197 eyes) was measured with both a disposable and the standard Goldmann tonometer (Goldmann). The level of agreement between the two methods of clinical measurement was assessed and the sensitivity and specificity of the disposable prism in detecting clinically significant raised IOP estimated. Results The mean difference in IOP measured by the two different prisms was 0.44 mmHg with a standard deviation (SD) of 1.54. The mean IOP for the disposable prism was 19.51 mmHg (SD 6.53 mmHg). The mean IOP for the standard Goldmann tonometer prism was 19.07 mmHg (SD 6.64 mmHg). The sensitivity to detect IOP > 21 mmHg was 95.9% (95% confidence interval (CI): 86.0-99.5%) and the specificity of 93.9% (95% CI: 88.8-97.2%). It gave a positive predictive value of 83.9% (95% CI: 71.7-92.4%). Conclusion There was close agreement between the IOP measurements obtained by the disposable tonometer prism and the Goldmann device for high and low pressures. If replicated, the high sensitivity and specificity would justify its use in screening.