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Mechanisms causing angle closure can be described according to the anatomical location of the obstruction

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Mechanisms causing angle closure can be described according to the anatomical location of the obstruction:

  • pupillary block mechanism
    • seen in around 75%
    • aqueous flow from the posterior chamber to the anterior chamber through the pupil is hampered resulting in an increase in posterior chamber pressure and anterior bowing of the iris
    • may be physiological (during reading in poor light) or pharmacological
    • narrow anterior segment and the age related increase of lens volume may act as predisposing factors
    • is associated with hypermetropia

  • obstruction at the level of the iris and/or cilliary body
    • caused by variation in anatomy of the iris and cilliary body resulting in iridotrabecular contact
    • e.g. - thick iris, more anterior iris insertion and more anterior cilliary body position

  • obstruction at the level of the lens
    • thicker (in diabetes or post traumatic cataract), more anteriorly positioned (retinal gas or oil tamponade) or subluxation (Marfan syndrome or trauma) of the lens may result in secondary angle closure

  • obstruction posterior to the lens (aqueous misdirection syndrome)
    • may be seen after trabeculectomy, lens extraction, laser iridotomy
    • aqueous is misdirected in to the vitreous causing lens/iris diaphragm to push forward and obstruct the anterior chamber angle (1)

Reference:

  • 1. European Glaucoma Society (EGS) 2008. Terminology and guidelines for glaucoma (3rd edition)

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