The effect of pharmacological pupillary dilation on intraocular pressure measurement.

Objective: To measure the difference in intraocular pressure (IOP) before and after pharmacologic mydriasis in normal subjects using Goldmann applanation tonometer (GAT) and the Diaton transpalpebral tonometer (DT).

Design: Prospective case series study.

Participants: Sixty-seven adult patients attending a tertiary general ophthalmology eye care center.

Methods: Patients were recruited based on a lack of glaucoma history and normal anterior segment on slit lamp examination. IOP measurements predilation and postdilation were collected. Predilation, both eyes were measured using GAT followed immediately by DT. Forty-five minutes post pharmacologic mydriasis, the measurements were repeated sequentially in the same order. Central corneal thickness (CCT) and additional parameters were also collected to corroborate the absence of glaucoma.

Results: Using GAT, the mean IOP predilation was 16.7 ± 3.1 mm Hg OD and 16.12 ± 3.0 mm Hg OS. The mean difference between predilation and postdilation time-points was -1.1 ± 2.5 mm Hg in the right eye and -0.7 ± 2.3 mm Hg in the left eye. Using DT, the mean IOP predilation was 12.8 ± 3.8 mm Hg OD and 13.2 ± 3.5 mm Hg OS. The mean difference between predilation and postdilation time points was -0.8 ± 4.0 mm Hg in the right eye and -0.7 ± 3.6 mm Hg in the left eye. There was a larger fluctuation of postdilation measurements using DT. The difference in IOP measured by the 2 instruments was statistically significant both predilation and postdilation (paired sample analysis pre-correlation 0.38 p = 0.002; post correlation 0.40 p = 0.001).

Conclusions: The use of pharmacologic mydriasis affected the reliability of IOP measurements which was decreased when taken postdilation by both GAT and DT. The poor agreement between GAT and DT values indicates an intrinsic difference between the two types of instrumentation.