Biomeasurement and analysis of the anterior chamber angle and related tissues in myopia eyes

Abstract

Background Myopia is one of the main blinding diseases worldwide.At present, a lot of studies on ocular structure focus on the changes of corneal curvature（CC), central corneal thickness (CCT), anterior chamber depth (ACD), ocular axial length (AL) and choroid and retina, but the research of anterior chamber angle section structure form and ciliary body shape is lack. Objective This study was to measure and analyze the changes of the anterior chamber angle and related tissue structure in myopic eyes. Methods One hundred and forty-nine eyes of 149 subjects were included from May 2008 to May 2010 in Eighth Hospital of Qingdao City with the ages of 18-40 years old under the informed consent.The subjects were assigned to the emmetropia group (30 eyes) ([0.02±0.18]D), low myopia group(46 eyes) ([-1.64±0.69]D), moderate myopia group (35 eyes) ([-4.56±0.66]D) and high myopia group(38 eyes) ([-7.04±1.02]D). Conventional indexes including intraocular pressure (IOP), CCT, CC, AL and ACD were measured, and the indexes including chamber angel open distance (AOD), iris thickness (IT1, IT2, IT3), the position of ciliary body such as A-angel, B-angel, trabecular ciliary process distance (TCPD), iris-ciliary process distance (ICPD) and ciliary body thickness (CBT1, CBT2, CBT3) were measured by ultrasound biomicroscope（UBM). Results The IOP, CC and CCT values showed slight change in different groups without remarkable difference among them (all at P>0.05). As the increase of myopic degree, AL was extended and ACD was deepened, showing significant differences among the groups (both at P 0.05). However, the measuring values of angle opening degree (TIA and AOD500), ciliary position (A-angle, B-angle, TCPD, ICPD) and CBT (CBT1, CBT2, CBT3) elevated with the increase of myopic degree (all at P<0.05). Positive correlations were found between AOD500 and ACD, A-angle, CBT1, CBT2, AL, negative correlations was found between AOD500 and myopic degree（r=0.573, 0.513, 0.325, 0.398, 0.542, -0.435, all at P<0.01); Positive correlations were found between TIA and ACD, A-angle, CBT1, CBT2, AL, negative correlations was found between AOD500 and myopic degree（r=0.573, 0.464, 0.276, 0.410, 0.539, -0.435, all at P<0.01). Conclusions Within certain limits, as the increase of myopic degree, ACD deepens, the anterior chamber angle widens, ciliary process thickens and ciliary body backward shifts. Key words: Biometry; Myopia; Microscopy, acoustic; Axial length; Anterior chamber/ultrasonography; Ciliary body/ultrasonography; Anterior chamber angle/ultrasonography