AIM: To evaluate volume differences between anterior and posterior orbit and demographic characteristics of Chinese patients with congenital microphthalmia. METHODS: A retrospective cohort study, involving 169 unilateral congenital microphthalmia patients aged between 1 and 57 years old was conducted. Three-dimensional images of the orbit were generated from past CT scans, and digital orbital volume comprehensive measurement was done. The measured data included orbital volume (OBV), posterior orbital volume (POV), orbital width (OBW), orbital height (OBH), orbital depth (OBD), and posterior orbital area ratio. RESULTS: Significant differences were observed among OBV, POV, OBW, OBH, and OBD of the affected and unaffected eyes in different age-based groups (all P<0.001). Among them, OBH had the greatest different. The mean microphthalmic to contralateral ratio (MCR) of OBV, POV, OBW, and OBH continuously increased from 1 to 3 years old, whereas the MCR of POV decreased from 3 to 17 years old. The MCR of OBD was not found to be correlated to age. There was no significant difference between OBV, POV, OBW, and OBH in ages from 13 years old to adulthood (all P>0.05). The difference in posterior orbital area ratio between the affected and unaffected groups was not statistically significant (P>0.05). CONCLUSION: OBH is maximally affected, whereas OBD is minimally affected by microphthalmia. Posterior orbital retardation began 2y prior to orbital retardation and occurred at 3 years old in the affected eye, suggesting that intervention therapy should be done before the age of 4.