Effects of Mydrin eye-drops on central corneal thickness values in adult patients with myopia.

OBJECTIVE: This study aimed to evaluate the effect of Mydrin eye-drops on central corneal thickness values and investigate the duration of the effect.

METHODS: In this prospective randomised self-controlled study, we enrolled 60 myopic patients (120 eyes) undergoing corneal laser refractive surgery. The central corneal thickness was measured before and one and four hours after administration of Mydrin eye-drops (major components are tropicamide and phenylephrine hydrochloride) using the Orbscan II anterior segment analysis system and a SP-2000P non-contact specular microscope, respectively.

RESULTS: Using the Orbscan II system, the baseline central corneal thickness (545 ± 27 µm) was significantly lower than that at one hour after Mydrin eye-drop application (559 ± 31 µm; p < 0.001); it was comparable to that at four hours post-Mydrin eye-drop administration (544 ± 26 µm; p < 0.74). Measured by non-contact specular microscopy, the baseline central corneal thickness (508 ± 26 µm) was significantly lower than that at one hour after Mydrin eye-drop application (521 ± 29 µm; p < 0.001); it was comparable to that at four hours after Mydrin eye-drop administration (506 ± 24 µm; p = 0.62). A significant difference was observed in the central corneal thickness at one and four hours after Mydrin eye-drop application by both methods (p < 0.001). Bland-Altman plots showed agreement between the measurements by the two methods at different times.

CONCLUSION: Central corneal thickness increases one hour after topical application of Mydrin eye-drops and is normalised at four hours following the administration of the drops. For patients scheduled to undergo excimer laser corneal refractive surgery, the central corneal thickness should be measured before or four hours after administration of Mydrin eye-drops.