Short-term effects of cyclopentolate and tropicamide eye drops on macular choroidal thickness in myopic children

Background: To investigate the short-term effects of cyclopentolate and tropicamide eyedrops on choroidal thickness (ChT) in myopic children using placebo or low-dose atropine eyedrops. Methods: The analysis included 242 myopic individuals (7–19 years) enrolled in two randomised placebo-controlled clinical trials of low-dose atropine eyedrops. Cycloplegia was induced using either one drop of 1% cyclopentolate (n = 161), two drops of 1% cyclopentolate (n = 32) or two drops of 1% tropicamide (n = 49). ChT measurements were taken using swept-source optical coherence tomography before and 30 min after administering the cycloplegic eye drops. A subset of 51 participants underwent test–retest measurements prior to cycloplegia. Results: Mean changes in subfoveal ChT after two drops of tropicamide and one and two drops of cyclopentolate were −2.5 μm (p = 0.10), −4.3 μm (p < 0.001) and −9.6 μm (p < 0.001), respectively. Subfoveal ChT changes after one and two drops of cyclopentolate were significantly greater than the test–retest changes (test–retest mean change: −3.1 μm; p < 0.05), while the tropicamide group was not significantly different (p = 0.64). Choroidal thinning post-cyclopentolate was not significantly different between atropine and placebo treatment groups (p > 0.05 for all macular locations). The coefficient of repeatability (CoR) in the tropicamide group (range: 8.2–14.4 μm) was similar to test–retest (range: 7.5–12.2 μm), whereas greater CoR values were observed in the cyclopentolate groups (one drop: range: 10.8–15.3 μm; two drops: range: 12.2–24.6 μm). Conclusions: Cyclopentolate eye drops caused dose-dependent choroidal thinning and increased variation in pre- to post-cycloplegia measurements compared with test–retest variability, whereas tropicamide did not. These findings have practical implications for ChT measurements when cyclopentolate is used, particularly for successive measurements.