Measurement of intraocular pressure after epikeratophakia

Aims - To assess the accuracy of three commonly used tonometers in eyes after epikeratophakia. Methods - Five eye bank eyes with sutured epikeratophakia buttons were connected to a manometer and a pressure transducer. Intraocular pressure was adjusted in 5 mmHg increments from 0 to 50 mmHg. The intraocular pressure was measured at each increment using a Goldmann tonometer, a pneumatonometer, and a Tono-pen. Results - The difference between the manometer (actual pressure) and the Goldmann tonometer ranged from -19 to +9 mmHg (mean (SD) overestimation 2.6 (5.8) mmHg). The pneumatonometer error ranged from -27.5 to +5.5 mmHg (mean (SD) overestimation 4.7 (6.1) mmHg), and for the Tono-pen the range was -18 to +11 mmHg (mean (SD) overestimation 0.05 (7.9) mmHg). The correlation coefficients for the three tonometers were 0.94, 0.92, and 0.87 for the Goldmann tonometer, pneumatonometer, and Tono-pen respectively. Conclusion - The Goldmann tonometer had the best correlation with the manometer in eye bank eyes with epikeratophakia (correlation coefficient 0.94), but none of the tonometers was accurate over the entire range of pressures tested. Detection of glaucoma in eyes with epikeratophakia cannot rely on tonometry alone, but requires examination of the optic nerve and visual field.