[Insights into shallow anterior chamber formation: from the perspective of fluid dynamics and trans-lens pressure...

Central anterior chamber depth (cACD), defined as the shortest distance between the posterior corneal surface and the anterior lens surface, is a key anatomical parameter for assessing the risk of primary angle-closure glaucoma (PACG). Traditional views often regard a shallow anterior chamber as a static anatomical consequence of a short axial length or a thickened lens; however, this perspective fails to fully explain the physiological fluctuations of cACD or the variability in angle-closure progression among individuals. Integrating recent high-resolution in vivo imaging and fluid dynamic evidence, this review explores the dynamic mechanisms underlying the formation of a shallow anterior chamber. We highlight that forward aqueous flow encounters a dual-bottleneck: cilio-lenticular block (proximal resistance) and pupillary block (distal resistance). When the cilio-lenticular space is severely compromised, aqueous flow is severely hindered and misdirects posteriorly, generating a substantial Trans-lens Pressure Difference (TLPD). Acting as the core mechanical driving force, TLPD pushes the entire lens-ciliary diaphragm forward, precipitating a shallowing of the anterior chamber. From this perspective, a shallow anterior chamber may be reinterpreted as the result of the combined effects of anatomic susceptibility and abnormal fluid dynamics. This understanding may offer important insights for the early identification of individuals at high risk for primary angle-closure glaucoma and for the development of individualized intervention strategies.