Objective To study the choroidal thickness of the macula subfovea using enhanced depth imaging spectral-domain optical coherence tomography （EDI-OCT） before dilation， after dilation， the following day after dilation. Methods Prospective clinical study. Fifty-eight patients （116 eyes） were dilated with tropicamide eye drops. All patients were examined with EDI-OCT before dilation， after dilation and the following day after dilation. Then， the eyes were scanned with a 8.8 mm scan line in the horizontal and vertical directions. Finally， the subfoveal choroidal thickness and the retinal thickness of the fovea were measured. Data were analyzed using independent t test and paired t test. Results Choroidal thickness after dilation was thinner than before dilation. The difference was statistically significant （right eye： t= 4.305， P＜0.01； left eye： t=5.007， P＜0.01）. Choroidal thickness after dilation was thinner than that measured the next day after dilation， and the difference was statistically significant （right eye： t=-3.237， P＜0.01； left eye： t=-3.011， P＜0.01）. However， the difference between choroidal thickness before dilation and the next day after dilation was not statistically significant （right eye： t=-0.300， P＞0.05； left eye： t=-0.333， P＞0.05）. There was no significant difference between binocular retinal values measured before dilation， after dilation， or the following day after dilation. Conclusion The choroid becomes thinner after using tropicamide eye drops when measured by EDI-OCT， which is noninvasive and intuitive to observe the subtle changes in living tissue after drug use.