Optometry school teaches doctors to perform their comprehensive eye exam in a particular order for a reason. If you think you can subvert that order to better manage your time, you may actually be making more, and unnecessary, work for yourself. A new study published in the Canadian Journal of Ophthalmology shows that dilating a patient before measuring their intraocular pressure (IOP) is a big no-no.

The researchers say the drugs used to dilate the pupil affect the reliability of IOP measurements, whether you’re using Goldmann applanation tonometry (GAT) or dilation transpalpebral (DT) tonometry. In either case, patients’ IOPs decreased when taken post-dilation. The investigators also noted a poor agreement between GAT and DT values, indicating an intrinsic difference between the two types of instrumentation.

The review focused on 67 patients, none of whom had a history of glaucoma. They all had normal anterior segments when examined behind a slit lamp. The investigators measured their IOPs pre- and post-dilation.

Using GAT, the mean IOP pre-dilation was 16.7±3.1mm Hg OD and 16.12±3.0mm Hg OS. The mean difference between pre-dilation and post-dilation time-points was −1.1±2.5mm Hg OD and −0.7±2.3mm Hg OS. Using DT, the mean IOP pre-dilation was 12.8±3.8mm Hg OD and 13.2±3.5mm Hg OS. The mean difference between pre- and post-dilation time-points was −0.8± 4.0mm Hg OD and −0.7±3.6mm Hg OS. There was a larger fluctuation of post-dilation measurements using DT.

Qian C, Hassanaly S, Duperré J, et al. The effect of pharmacological pupillary dilation on intraocular pressure measurement. Can J Ophthalmol. December 25, 2019. [Epub ahead of print].