When patients present for a standard checkup and refraction, most have their intraocular pressures (IOP) tested with non-contact tonometry. For this, they’re seated in front of the air puff device. But for some—such as glaucoma suspects, patients who need regular IOP monitoring and individuals tested outside the clinic—these air puff tests may not be ideal.

For those who need them, an array of other IOP testing methods are available, and doctors may apply some while the patient is in the supine position. However, researchers are now showing that all IOP readings should be performed in the seated position. They found that taking the measurement itself can cause the patient’s pressures to rise, and that rise is significantly greater—and riskier—when performed in the supine position compared with sitting.

The researchers looked at 24 healthy adults and asked them to read a text on a smartphone 30cm away for 25 minutes while lying down and then invited them back the next day to perform the same task while seated. Each day, a rebound tonometer measured their IOPs before the reading and at three points (five, 15 and 25 minutes) during the reading, as well as five minutes after. The researchers took into account each subject’s level of alertness before reading and the perceived levels of fatigue and discomfort after.

They were able to show that reading induces an IOP rise and that the effect was more accentuated when the subjects were in the supine position compared with the seated position, with a specific increase of 2.4mm Hg (14%) in the supine position and 1.3mm Hg (8%) in the seated position after 25 minutes of reading.

Participants reported greater levels of discomfort in the neck and back when reading in sitting position. No differences were noted between male and female subjects (of which the study had 12 of each).