Accuracy of clinical estimates of intraocular pressure in Chinese eyes

Purposes To investigate the validity of clinical estimates of intraocular p ressure (IOP) in Chinese people. Design: Prospective, cross-sectional, hospital-based in vivo study. Participants: Twenty-three ethnic Chinese adults (aged 35-82 years) undergo ing routine phacoemulsification surgery were examined. Testing: "True" IOP was measured with a solid-state hemodynamic monitor thr ough a cannula in the anterior chamber. IOP was set successively to 10, 20, and 30 mmHg in each subject, using a reservoir of balanced salt solution. Intraocular pressure was simultaneously estimated by use of a hand-held app lanation tonometer (Perkin's) and a Tone-Pen. The association between ocula r biometric variables and measurement error was examined. Main Outcome Measures: The median of three readings at each IOP level was t aken as the IOP estimate of each instrument. Measurement error was calculat ed as the mean difference (tonometer minus direct measurement). Results: The error for the hand-held applanation tonometer was -1.6, -4.3 a nd -5.7 at 10, 20, and 30 mmHg, respectively. For the Tone-Pen the measurem ent error was +0.4, -2.0, and -4.1 at 10, 20, and 30 mmHg, respectively. We could identify no association between measurement error and corneal thickn ess or curvature, anterior chamber depth, or axial length. Conclusions: The applanation tonometer and Tone-Pen underestimate the true IOP in Chinese eyes. Error increases as true IOP increases. These tonometer s do not give an accurate estimate of IOP in East Asians. Ophthalmology 200 0; 107:1816-1821 (C) 2000 by the American Academy of Ophthalmology.