Cycloscopy of angle-closure glaucoma

Prevalence and mechanism of appositional angle closure in acute primary angle closure after iridotomy

PURPOSE

A prospective observational case series to assess the prevalence of appositional angle closure in darkness among iridotomized Chinese eyes after acute primary angle closure (APAC) with the use of both clinical methods and ultrasound biomicroscopy.

METHODS

Sixteen Chinese patients who had history of APAC and subsequent successful treatment with laser peripheral iridotomy were examined. Fourteen additional control subjects were studied. Gonioscopy and ultrasound biomicroscopic examination were performed in the dark. Gonioscopic appearance of the angle was assessed, and quantitative measurements of the angle from the ultrasound biomicroscopic images were taken.

RESULTS

Of the APAC eyes 55.6% had appositionally closed angle clinically and in 38.9% only Schwalbe's line was visible on gonioscopy. Ultrasound biomicroscopy confirmed structurally different anterior segments between eyes with APAC and the control eyes. In particular, the trabecular-ciliary-process distances were markedly different between the two groups.

CONCLUSION

This study documented a high prevalence of appositional closure in iridotomized eyes after APAC in Chinese patients. The anteriorly positioned ciliary body, as documented in these cases by ultrasound biomicroscopy, is the likely mechanism of the angle crowding in this patient population.

Predisposing factors for chronic angle-closure glaucoma

Chronic angle-closure glaucoma is the commonest form of glaucoma in Sino Mongaloid populations. It is an anatomical disorder of the anterior segment of the eye characterised by permanent closure of part of the filtration angle as a result of iris apposition to the trabecular meshwork. Two pathways lead to this condition: recurrent pupillary block and "creeping" angle closure. East or Southeast Asian ethnic background is an important risk factor for the development of chronic angle-closure glaucoma. Other demographical risk factors include ageing, female gender and a familial tendency. Eyes with chronic angle-closure glaucoma have different anterior segment anatomical relationships when compared to normals. Those eyes at risk tend to be hypermetropic with a shallow anterior chamber, a relatively anteriorly positioned lens and a short axial length. The role of the ciliary body anatomy and ciliary processes in the pathogenesis of this condition requires further investigation.