Intraocular pressure asymmetry in a population tested with the Pulsair non-contact tonometer

Intraocular pressure asymmetry as measured by noncontact tonometry (NCT) was analysed in a population of 874 individuals aged over 50 years. In both males and females the intraocular pressure (IOP) measured in the right eye exceeded that of the left. Pressure asymmetry followed a normal distribution in a population subgroup known to have normal fields, discs and pressures. The 95% confidence intervals for the equation R IOP--L IOP in normals were 0.63+ or -5.46 mmHg when the mean of four pulses per eye were used to calculate the IOP, increasing to 0.80+ or -6.56 mmHg for two pulses per eye (thus expanding the limits by 20%). The range of asymmetry for NCT in normals therefore exceeds that reported for Goldmann applanation tonometry. Asymmetry was greater in females than males. Knowledge of the normal range of IOP asymmetry in each sex will help glaucoma screeners using NCT in their decision as to when to refer. A minimum of four pulses per eye should be used to assess the IOP when screening.