Changing trends of imaging in angle closure evaluation

Abstract

Primary angle closure glaucoma (PACG) is a significant cause of visual disability worldwide. It predominantly affects the Eastern and South Asian population of the world. Early detection of anatomically narrow angles is important, and the subsequent prevention of visual loss from PACG depends on an accurate assessment of the anterior chamber angle (ACA). Gonioscopy has given way to modern day imaging technologies such as ultrasound biomicroscopy (UBM) and more recently, anterior segment optical coherence tomography (AS-OCT). Ultrasound biomicroscopy provides objective, high-resolution images of anterior segment anatomy, including the cornea, iris, anterior chamber, anterior chamber angle, and ciliary body. Optical coherence tomography (OCT) is a noncontact optical signal acquisition and processing device that provides magnified, high-resolution cross-sectional images of ocular tissues. Recent technological advances towards three-dimensional visualization broadened the scope of AS-OCT in ophthalmologic evaluation. Optical coherence tomography systems use low-coherence, near-infrared light to provide detailed images of anterior segment structures at resolutions exceeding that of UBM. This paper summarizes the clinical application of UBM and OCT for assessment of anterior segment in glaucoma.

Figure 1

Ultrasound biomicroscopy image showing normal angle structures. S: sclera; CB: ciliary body, PC: posterior chamber, AC: anterior chamber, L: lens, C: cornea. Dark arrows delineate the trabecular meshwork from the scleral spur towards schwalbe's line while the white arrow signals points towards an open angle.

Figure 2

UBM image showing relative pupillary block with bowing of the iris anteriorly prior to laser iridotomy.

Figure 3

Ultrasound biomicroscopy image showing plateau iris with the classic double-hump sign. Contrary to angle closure on the basis of relative pupillary block, where indentation gonioscopy results in deepening of the peripheral anterior chamber, in plateau iris the iris contour follows the lens, dips posteriorly, then rises anteriorly before reaching the angle recess. The iris root remains angulated forward with a deepening of the anterior chamber confined to the region of the central iris. In this figure iridotrabecular contact (ITC) can be appreciated.

Figure 4

Ultrasound biomicroscopy image showing peripheral anterior synechia (PAS). S: sclera; CB: ciliary body, AC: anterior chamber, I: iris, C: cornea. Dark arrows delineate the PAS.

Figure 5

Ultrasound biomicroscopy image of an eye with plateau iris configuration status post-argon laser peripheral iridoplasty (PICP). An open angle and no ITC can be appreciated.

Figure 6

Ultrasound biomicroscopy image showing angle closure consequent of phacomorphic causes. A large lens is pushing iris anteriorly causing angle closure.

Figure 7

Ultrasound biomicroscopy image showing anteriorly rotated ciliary body in aqueous misdirection/ciliaryblock/malignant glaucoma.

Figure 8

Anterior segment optical coherence tomography image showing relative pupillary block. AC: anterior chamber; ITC: iridotrabecular contact.

Figure 9

Anterior segment optical coherence tomography image showing plateau iris configuration. CB: ciliary body, AC: anterior chamber, ITC: iridotrabecular contact.

Figure 10

Anterior segment optical coherence tomography image showing angle closure consequent of phacomorphic causes.

Figure 11

Anterior segment optical coherence tomography image showing iridotrabecular and iridocorneal contact in a case of aqueous misdirection/ciliaryblock/malignant glaucoma.