To assess and compare the effects of cycloplegia using 0.5% tropicamide and 1% tropicamide on intraocular pressure (IOP) in patients with diabetes mellitus, with and without considering adjustments for central corneal thickness (CCT).

A total of 98 eyes of 98 patients with open angles were included. Patients were randomly assigned to receive either 0.5% tropicamide (49 eyes) or 1% tropicamide (49 eyes). IOP was measured by Goldmann applanation tonometry. Pupillary diameter and CCT were measured by a Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) before and 30 min after tropicamide administration.

The mean IOP change was 0.12 ± 1.71 mmHg in the 0.5% tropicamide group and 0.25 ± 1.70 mmHg in the 1% tropicamide group. These two values were not significantly different, even after adjusting IOP for CCT using all formulae (P > 0.05). Without adjustment, the mean post-dilation IOP was similar to the mean pre-dilation IOP in both groups (P > 0.5), and none of the patients experienced an IOP increase of 5 mmHg or more. With adjustment, the mean IOP increased significantly after administration of 0.5% tropicamide, as determined by the Ehlers formula (P = 0.02). Similarly, the mean IOP increased significantly after administration of 1% tropicamide, as determined by the Ehlers formula (P = 0.008), the Doughty formula (P = 0.03), and the Kohlhaas formula (P = 0.04). In each study group, a single patient encountered an increase in IOP ≥5 mmHg when IOP adjustment was performed using the Ehlers formula.

Cycloplegia with 0.5% and 1% tropicamide leads to similar mean changes in IOP in patients with diabetes. However, the statistical significance of the change and the occurrence of the significant increases in IOP, as determined by a predefined cut-off point, are dependent upon the method used to adjust the IOP.