Automatic Evaluation of the Anterior Chamber Angle Width by a New Non-contact Optical Device

Worldwide, glaucoma has been identified as a leading cause of blindness, second only to cataract. The two most common types of glaucoma are primary open-angle and angle closure glaucoma (PACG), both characterized by progressive and irreversible degeneration of the retinal ganglion cells and axons. In PACG, the optic neuropathy occurs as a consequence of raised intraocular pressure (IOP) resulting from physical obstruction of aqueous outflow or degenerative changes in the trabecular meshwork. Angle closure is the result of an anatomic characteristic that causes closure of the drainage angle by synechial or appositional approximation between the iris and the trabecular meshwork, blocking access to aqueous humor. Although the most common mechanism responsible for angle closure is relative pupillary block, this is not the only one. Angle crowding can be caused by plateaus iris, or by multiple mechanisms such as choroidal thickness and uveal expansion.

A careful analysis of the anterior chamber angle is considered the main management strategy for PACG. The Van Herick grading of limbal anterior chamber depth is considered a screening tool for the estimation of angle width although gonioscopy remains the clinical reference standard for assessing the presence of narrow or closed angle. Ultrasound biomicroscopy, Scheimpflug imaging and anterior segment optical coherence tomography are considered as non-invasive alternatives to gonioscopy. However, these techniques are expensive and also have drawbacks. Therefore, there is a need for an easy and objective method able to evaluate the angle width for screening purposes in clinical practice.

Based on these findings, the purpose of the present study is to evaluate an objective, non-invasive optical device able to quantify, without eye contact, the width of the irido-corneal angle and to better identify cases of narrow angle or angle closure that may be prevented with relatively simple treatments.