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To investigate changes in the corneal shape caused by fluid-gas exchange after vitrectomy.This retrospective case-control study included 43 eyes that underwent a combination of cataract surgery and vitrectomy. The corneal shape was measured using anterior segment optical coherence tomography CASIA2. The corneal shape measurements were performed preoperatively, 1 day, 1 week, 1 month, and 3 months after surgery. After calculating the real K value from the actual measured values of the posterior shape of the corneal refracting power and the single posterior corneal refracting power value, Fourier analysis values were examined. Fluid-gas exchange was performed in 23 eyes (gas group), while it was not performed in 20 eyes (nongas group).There was a significant increase in the real K value in the regular and asymmetry components (0.61 ± 0.36, 0.82 ± 0.64) in the gas group only on the first day after surgery (Steel-Dwass test; P < .05). There was also a significant increase in the real K value in the higher-order irregular astigmatism components (Steel-Dwass test; P < .05) for longer periods in the gas versus the nongas group. The shape of the posterior cornea increased in all components in the gas group on the first day after surgery (spherical power À6.35 ± 0.20, regular astigmatism 0.32 ± 0.12, asymmetry 0.22 ± 0.13, and higher-order irregular astigmatism 0.12 ± 0.05, Steel-Dwass test; P < .05).Postoperative changes caused by surgical invasion in the corneal shape appeared to be greater in the gas versus the nongas group, in addition to affecting the time periods of the postoperative corneal shape changes.