Clinical Analysis Of Anterior Segment Structure In Early Stage Of Primary Angle-closure Glaucoma

Objective:To measure quantitatively the structural parameters of anterior segment in patients with primary angle closure glaucoma（PACG）and normal subjects by using ultrasound biomicroscopy（UBM）,and compare the differences of these biological parameters between patients with different PACG（acute,chronic）and normal subjects to understand the relationship between the anatomical changes of the anterior segment and the pathogenesis of different types of PACG.Method:Retrospective study.Seventy-five patients（75 eyes）with unilateral primary angle-closure glaucoma treated in the affiliated Eye Hospital of Nanchang University from January 2018 to December 2021 were selected,45 cases（45 eyes）of acute primary angle-closure glaucoma and 30 cases（30 eyes）of chronic primary angle-closure glaucoma,and 22 healthy subjects（22 eyes）who underwent eye physical examination in the same period were selected as the control group.All the selected patients underwent comprehensive ophthalmo-logical examination,including visual acuity,intraocular pressure,ocular fundus,visual field,gonioscopy,optic disc OCT,and ultrasound biomicroscopy（UBM）.In the qualified UBM images,the anterior chamber depth（ACD）,anterior chamber width（ACW）,anterior chamber area（ACA）and lens vault（LV）were measured by camera measure,and the relative position of lens vault（RPLV）and anterior segment depth（ASD）were calculated.At the same time,the anterior chamber angle opening distance at 500μm(AOD₅₀₀),trabecular iris area at 500μm(TISA₅₀₀),trabecular iris angle（TIA）,iris thickness at500μm(IT₅₀₀),peripheral iris maximum thickness(PIT_max)and iris curvature（IC）were measured and the average values were calculated.The data were analyzed by SPSS26.0,and the differences of ACD,ACW,ACA,LV,RPLV,ASD,AOD₅₀₀,TISA₅₀₀,TIA,IT₅₀₀,PIT_maxand IC between the preclinical stage of acute primary angle closure glaucoma,the early stage of chronic primary angle closure glaucoma and the normal group were compared.Analyze the influencing factors and weights ofACA in different types of PACG.ANOVA was used to analyze the differences of biological parameters among the three groups,independent sample t-test and chi-square test were used to compare the differences between two groups,P<0.05 is considered to be statistically significant.The correlation between parameters was analyzed by Pearson correlation analysis and multivariate linear regression analysis.Result:1.The parameters of preclinical primary acute angle-closure glaucoma（APACG）were:ACD（1.887±0.227）mm,ACW（11.454±0.524）mm,ACA（11.122±1.812）mm²,LV（1.116±0.214）mm,RPLV（0.371±0.064）mm,ASD（3.004±0.234）mm,AOD₅₀₀（0.053±0.032）mm,TISA₅₀₀（0.022±0.014）mm²,TIA（6.256±3.759）°,IT₅₀₀（0.382±0.059）mm,PIT_max（0.502±0.071）mm.IC（0.283±0.096）mm.2.The parameters of early primary chronic angle-closure glaucoma（CPACG）were:ACD（1.936±0.284）mm,ACW（11.551±0.537）mm,ACA（11.993±2.354）mm²,LV（0.998±0.236）mm,RPLV（0.341±0.081）mm,ASD（2.934±0.197）mm,AOD₅₀₀（0.034±0.032）mm,TISA₅₀₀（0.015±0.014）mm²,TIA（3.808±3.479）°,IT₅₀₀（0.385±0.065）mm,PIT_max（0.537±0.071）mm.IC（0.241±0.074）mm.3.The parameters of normal control group were:ACD（2.750±0.147）mm,ACW（11.712±0.340）mm,ACA（19.440±2.007）mm²,LV（0.384±0.178）mm,RPLV（0.121±0.054）mm,ASD（3.134±0.141）mm,AOD₅₀₀（0.372±0.133）mm,TISA₅₀₀（0.131±0.045）mm²,TIA（37.957±10.966）°,IT₅₀₀（0.394±0.055）mm,PIT_max（0.502±0.044）mm,IC（0.127±0.044）mm.4.The anterior chamber parameters（ACD,ACW,ACA）,anterior chamber angle parameters(AOD₅₀₀,TISA₅₀₀,TIA)and anterior segment parameter（ASD）in preclinical APACG group and early CPACG group were lower than those in normal control group,while lens parameters（LV,RPLV）and part of iris parameters（IC）were significantly higher than those in normal control group（P<0.05）.AOD₅₀₀,TISA₅₀₀,TIA,LV and IC in preclinical APACG were higher than those in early CPACG,while PIT_maxwas lower than that in early CPACG（P<0.05）.There was no statistical significance in ACD,ACW,ACA,RPLV,ASD and IT₅₀₀between the two groups.5.Linear regression formulaIn preclinical APACG group:ACD,ACW,ASD,IT₅₀₀and PIT_maxare positively correlated with ACA,while LV,RPLV and IC are negatively correlated.ACD has the strongest correlation.In early CPACG group:ACD,ASD,and IT₅₀₀are positively correlated with ACA,while LV,RPLV and IC are negatively correlated.ACD was the strongest correlation.Conclusion:1.The preclinical APACG,compared with the early CPACG,is closer to the anterior position of lens and the degree of iris curvature is greater,suggesting that the pathogenesis of APACG may be closely related to the abnormal position of lens and iris bulge,while the early CPACG has thicker peripheral iris,suggesting that the main cause of CPACG may be the narrowing of anterior chamber angle caused by peripheral iris thickening.2.The change of anterior chamber area in early PACG patients may be related to anterior chamber depth,anteiror segment depth,lens vault,relative position of lens vault,iris thickness and iris curvature,among which the anterior chamber depth has the greatest influence.3.RPLV may have a greater impact on the anterior chamber area of patients with PACG than LV,suggesting that RPLV has higher clinical value and is worth popularizing.