Comparison between standard Goldmann applanation prism and disposable applanation prism in tonometry

BACKGROUND: Disposable devices are increasingly becoming the preferred choice where possible in contact medical equipment. AIM: To evaluate the accuracy of the disposable applanation tonometer head as a potential substitute to the standard Goldmann applanation head. METHODS: The study was prospective. The intraocular pressure recordings in 80 eyes of 42 patients were compared using the disposable and standard Goldmann applanator heads. The Bland and Altman method of assessing agreement between two methods of clinical measurement was used in the analysis. RESULTS: The difference in the readings between the two types of tonometer heads was highly variable (mean difference=0.78 mm Hg, range=-1 to 11 mm Hg). This was because of the distortions on the applanating surface of the disposable device. When the readings associated with the defective heads were excluded, very strong agreement was obtained (mean=0.07 mm Hg, range=-1 to 2 mm Hg). CONCLUSION: Good agreement with standard Goldmann applanation is achieved with the disposable heads except where surface distortions induce significant errors. Careful inspection to ensure well-structured disposable units is imperative in disposable applanation tonometry.