Abstract
Purpose To explore the anatomical characteristics and occurrence mechanisms of acute primary angle closure (APAC) by comparing the quantitative data of UBM images of the APAC and fellow eyes. Methods 131 patients (262 eyes) were studied over five years by retrospective analysis. The quantitative data from UBM images including angle opening distance at 500 μm (AOD500), trabecular-iris angle (TIA), iris convexity (IC), iris span (IS), iris-lens angle (ILA), iris-lens contact distance (ILCD), iris-ciliary process angle (ICPA), and limbus-ciliary body angle (LCBA) were retrospectively recorded; comparative analysis of the APAC and fellow eyes was performed. Results The superior, inferior, nasal, temporal, and mean AOD500, TIA, IC, and LCBA (P < 0.001) were significantly smaller in APAC than in fellow eyes. Values of the lens thickness (LT), lens/axial length factor (LAF), lens position (LP), and relative lens position (RLP) were lower in APAC than in fellow eyes (P = 0.021; P = 0.025; P < 0.001; and P < 0.001). In APAC eyes, AOD500 was significantly positively correlated with IC, ILCD, and LCBA; TIA was significantly positively significantly correlated with IC, ILCD, and LCBA. In fellow eyes, AOD500 was significantly negatively correlated with ILA and significantly positively correlated with ILCD, ICPA, LCBA, axial length (AL), central anterior chamber depth (CACD), and LP; TIA was significantly negatively correlated with ILA and significantly positively correlated with IS, ILCD, ICPA, LCBA, AL, CACD, LP, and RLP. Conclusions Multiple nonpupillary block factors (plateau iris, anterior attachment and insertion of the iris root, anterior shift of the lens, and anterior rotation of the ciliary body) promote the occurrence of APAC, and abnormal positional relationships of the iris, ciliary body, and lens may contribute to APAC.
Highlights
Glaucoma is the second leading cause of blindness globally, after cataract [1, 2]
Shabana et al and Kwon et al [25, 26] utilised anterior segment optical coherence tomography (AS-OCT) to analyse the images of patients with PAC and classified angle closure mechanisms into four categories: (1) pupillary block (PB): bowing of the iris into a convex form, accompanied by a shallow central anterior chamber depth; (2) plateau iris configuration (PIC): the peripheral iris rises from the root and is extremely close to the trabecular wall of the chamber angle; at a certain point, there is a sharp turn of the iris away from the chamber angle, accompanied by a flat central iris and a relatively deep central anterior chamber; (3) thick peripheral iris roll (TPIR): 0.40 0.30 0.20 0.10
A relatively thick iris with significant peripheral circumferential folds and a chamber angle occupying a higher proportion of space; and (4) exaggerated lens vault (ELV): the lens pushes the iris anteriorly, resulting in a shallower anterior chamber and narrower chamber angle, which is clinically known as the “volcano-like configuration.”
Summary
Glaucoma is the second leading cause of blindness globally, after cataract [1, 2]. Estimates show that primary angle closure glaucoma (PACG) will account for almost 50% of all cases of binocular blindness by 2020 [6]. The Primary Angle Closure Preferred Practice Pattern (PPP) published by the American Academy of Ophthalmology in 2016 [7] states that acute angle closure crisis (AACC) is often accompanied by acute anterior chamber angle blockage and a rapid rise in intraocular pressure (IOP) to extremely high levels, and it may rapidly cause corneal edema (blurred vision, iridizations), moderate pupil dilation, conjunctival hyperaemia, and eyeball pain, which may be accompanied by symptoms such as headache, nausea, and vomiting. Fellow eyes of patients with AACC are at high risk of developing AACC
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