Accuracy of Perkins applanation tonometry and pneumatonometry in infants and children. A manometric study in vitro

Purpose. There is a well documented difference in measured intraocular pressure (IOP) between the pneumatonometer (PT) and the Perkins applanation tonometer (AT) in eyes of infants and children. This is a pilot report of an ongoing study to determine if this discrepancy can be reproduced in vitro with cadaver eyes, and if so, to determine the more accurate instrument. Methods. Eyes from children less than 12 years of age were requested from the eyebank. A surgical microscope was used to insert a 27g needle through the limbus, advanced through the pupil for standard posterior chamber perfusion. The wound was sealed with cyanoacrylate glue. Constant pressure perfusion at 10 mmHg with Barany's solution at 25°C was done for one hour to fully inflate and hydrate the eyes. Pressure measurements were taken three times with each instrument, AT then PT. Simultaneous pressure transducer readings were recorded with each tonometry. IOP was reset to 10 mmHg before each tonometry. Results. One pair of eyes from a four day old infant met the inclusion criteria. Measured IOP for eye 1 was 4.7 ± 1.53 (mean ± standard error in mmHg) using AT and 12.7 ± 0.58 using PT. Eye 2 was 4.0 ± 2.83 for AT and 17.7 ± 1.04 for PT. Conclusions. These data appear to agree with prior clinical reports of lower measured IOP with AT than with PT in very young eyes. Future work will investigate this more thoroughly and attempt to explain this discrepancy.