AIM: To investigate the characteristics of anterior segment structure in first-degree relatives of patients with primary angle-closure glaucoma(PACG).METHODS: A total of 48 first-degree relatives of PACG patients aged 40-60 who were treated in the Affiliated Eye Hospital of Nanchang University from September 2020 to October 2022 were selected as the observation group. Additionally, 40 cases(40 eyes)of healthy individuals without glaucoma and family history of glaucoma at the same age group were collected as the control group. They were divided into younger group(40-49 years old)and elder group(50-60 years old). All subjects were examined with ultrasound biomicroscopy(UBM)and were measured using camera measure software. The parameters mainly included anterior chamber depth(ACD), anterior chamber area(ACA), anterior chamber width(ACW), anterior segment depth(ASD), angle open distance(AOD500), trabecular iris angle(TIA), trabecular iris area(TISA500), lens vault(LV), iris curve(IC), iris thickness(IT500), scleral ciliary process angle(SCPA), and iris ciliary process distance(ICPD).RESULTS: ACD, ACA, AOD500, TISA500 and TIA in the observation group were lower than those of the control group, and LV and IC were higher than those of the control group(all P<0.05). ACD, ACA, AOD500, TISA500, and TIA of the elder group were lower than those in the age-matched control group, while LV and IC were larger than those of the age-matched control group(all P<0.05). ACD, AOD500, TISA500, and TIA of the younger observation group were smaller than those of the age-matched control group, but LV and IC were significantly larger than those of the age-matched control group(all P<0.05). ACD, ACA, AOD500, TISA500 and TIA of the elder observation group were significantly lower than those of the younger observation group, and LV and IC were significantly larger than those of the younger observation group(all P<0.05). There was a difference in the distribution of ACD between the observation group and the control group(P<0.05), and the proportion of moderate to severe shallow anterior chambers was 10 times that of the control group. Correlation analysis showed that TISA500 was positively correlated with ACD and ACA, and negatively correlated with LV and IC, and TISA500 was mainly influenced by LV. IC had a positive correlation with LV and a negative correlation with ACD and ACA.CONCLUSION: First-degree relatives of PACG with normal axial length have a high risk of angle closure. The anterior segment structures of first-degree relatives of PACG are more crowded than normal individuals, and the lens forward shift may be the initial influencing factor for narrow angle.