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Editors Selection IGR 17-4

Examination methods: UBM gonioscopy

Comment by Robert Ritch on:

11945 Effects of orbital venous pressure on intraocular pressure and ocular blood flow, Reitsamer HA; Kiel JW, Spektrum der Augenheilkunde, 2004; 18: 230-233

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Several reports in recent years have examined the value of both ultrasound biomicroscopy (UBM) and gonioscopy independently and comparatively in an effort to assess the occludability of narrow angles in an attempt to determine which patients should undergo laser peripheral iridotomy, particularly in Asia, where angle-closure is especially common. Kunimatsu et al. (108) sought to determine the prevalence of appositional angle closure in eyes with a shallow peripheral anterior chamber as detected by the van Herick (peripheral anterior chamber depth ≤1/4 corneal thickness) in the absence of peripheral anterior synechiae (thus eliminating incontrovertible cases) in Japanese patients. The angle was graded using the Shaffer method with a Goldmann lens and, when necessary to rule out the presence of PAS, by indentation gonioscopy. The presence of appositional angle closure was determined with UBM in each quadrant under light and dark conditions. The angle was most frequently narrower in the superior quadrant, a fact long known, and angles narrowed significantly in the dark. Appositional closure was found in at least ¹ quadrant in 46 (57.5%) of 80 eyes in light and in 68 eyes (85%) in the dark. The angle width, evaluated with conventional gonioscopic grading, and the quadrant of the angle were significantly related to the presence of appositional angle closure. Although use of the Goldman lens may potentially cause artifacts neither of these interferes with the basic conclusions of this report, which is that a large fraction of Japanese patients with a narrow peripheral iridocorneal angle on slit-lamp examination have potentially occludable angles.

The authors also discuss the separation of angle configurations into S-and B-type (closure initially from above (S) and below (B)).² The S-type angle was first noted by Mapstone,³ who suggested that angle-closure could begin with iridocorneal apposition to the angle wall at the level of Schwalbe's line prior to the development of iridotrabecular contact. This configuration was eventually proven to exist with UBM⁴ and later termed the S-type configuration by Sakuma et al.

Although the authors state that it is difficult to speculate from the present study as to the mechanism of formation (top or bottom) of PAS, it is entirely logical that both methods can occur, beginning in each ase at the site of appositional closure. In B-type angles, which are prone to 'creeping' angle-closure,⁵ PAS can begin at the apex of the angle, while in S-type angles, PAS can start at the site of contact between the peripheral iris and the upper trabecular meshwork. The former would result in gradual anterior progression of the apparent iris insertion, while the latter would result in tented PAS of varying extent.

Editor's NoteThis is good to know and the next answer will come from a longitudinal study: how many eyes with appositional closure will develop raised IOP and angle closure glaucoma and after what time period? Are there any predictive factors?

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