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Concept
Chambre antérieure de l'œil
Résumé
The anterior chamber (AC) is the aqueous humor-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Hyphema, anterior uveitis and glaucoma are three main pathologies in this area. In hyphema, blood fills the anterior chamber as a result of a hemorrhage, most commonly after a blunt eye injury. Anterior uveitis is an inflammatory process affecting the iris and ciliary body, with resulting inflammatory signs in the anterior chamber. In glaucoma, blockage of the trabecular meshwork prevents the normal outflow of aqueous humour, resulting in increased intraocular pressure, progressive damage to the optic nerve head, and eventually blindness.
The depth of the anterior chamber of the eye varies between 1.5 and 4.0 mm, averaging 3.0 mm. It tends to become shallower at older age and in eyes with hypermetropia (far sightedness). As depth decreases below 2.5 mm, the risk for angle closure glaucoma increases.
Determining the anterior chamber depth (ACD) is important in estimating the risk of angle closure glaucoma. There are various method of measuring ACD, including examination through a slit lamp, ultrasound and Scheimpflug photography. These methods require sophisticated examination equipment and expertise.
A simpler clinical method of quantitatively estimating ACD using smartphone photography (EZ ratio) was developed by Dr Ehud Zamir from the Centre for Eye Research Australia, the University of Melbourne, and published in 2016.
The EZ ratio method is one way to calculate the estimated anterior chamber depth. To start, the patient looks at a target in the distance with one eye covered. The examiner takes a digital photograph of the open, examined eye, from the side, perpendicular to the visual axis (a profile photograph).
The following parameters then need to be measured in the photograph, using a personal computer or a smartphone (figures 1,2):
- The pixel distance between the limbus (the junction between clear cornea and white sclera) and the front of the cornea.
Source officielle
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