Objective  To compare the difference of central corneal thickness (CCT) before and after mydriasis measured with A-ultrasound pachymetry and Pentacam three-dimensional anterior segment analysis system.

  Methods  From August 2011 to November 2011, the CCT of 130 eyes from 65 adult patients with myopia in Peking Union Medical College Hospital were measured with A-ultrasound pachymetry and Pentacam Scheimpflug system before and after mydriasis using compound tropicamide eye drops.

  Results  The CCT values obtained with A-ultrasound pachymetry before and after mydriasis were (536.70±39.60)μm and (548.31±39.22)μm, respectively. The value after mydriasis was significantly higher than that before mydriasis (P=0.000). The CCT values obtained with Pentacam three-dimensional anterior segment analysis system before and after mydriasis were (539.57±39.73)μm and (545.99±39.47)μm, respectively. The value after mydriasis was also significantly higher than that before mydriasis (P=0.000). CCT value obtained with Pentacam three-dimensional anterior segment analysis system was significantly higher than A-ultrasound pachymetry before mydriasis (P=0.000); however, there was no significant difference in CCT between the two methods after mydriasis (P=0.081).

  Conclusions  Values of CCT measured after mydriasis are higher than before mydriasis. Therefore, the values of CCT measured before mydriasis may be more accurate, which can help to provide a better option for choosing operative methods and evaluating the safety of refractive surgery.