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Lens vault may play role in development of acute primary angle closure
Researchers found lens vault to be greater in eyes with acute primary angle closure vs. unaffected eyes in the same patient, according to a study recently published in Investigative Ophthalmology & Visual Science.
Lee and colleagues evaluated 36 patients with unilateral acute primary angle closure (APAC) to investigate differences in anterior segment parameters.
All participants underwent a comprehensive ophthalmic examination. Researchers utilized ImageJ software (version 1.46, provided in the public domain by the National Institutes of Health) to measure anterior chamber depth (ACD), lens vault, anterior chamber area (ACA), iris curvature and iris thickness at 750 μm from the scleral spur. They also imaged patients with anterior segment optical coherence tomography (OCT) before medical treatment.
Additionally, researchers performed several conditional logistic regression analyses to identify factors related to the prediction of APAC.
Results showed that eyes affected with APAC had a significantly shallower ACD, smaller ACA and greater lens vault. Researchers also reported that less iris curvature, greater lens vault, greater central corneal thickness, less ACA and less ACD were all significantly associated with the prediction of APAC.
"Our data revealed increased lens vault as the most distinguishing feature of acute attack–affected eyes compared to fellow eyes," the authors concluded. "Flatter iris despite pupillary block may be due to pushing of the central portion of the iris due to increased lens vault. Thus, pupillary block and elevated lens vault may play a combined role in inducing acute attack. Furthermore, increased lens vault may aggravate pre-existing relative pupillary block.
"Considering that both mechanisms contribute to the development of acute attack in PAC, resolving two issues, that is, the increase in lens vault and pupillary block, is necessary to treat acute attack in patients with angle closure," they continued. "In case of persistent IOP elevation despite laser peripheral iridotomy, careful extraction of the lens might be a therapeutic option in APAC eyes when increment of lens vault is observed."
Disclosure: The authors have no relevant financial disclosures.
Perspective
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Acute angle closure is a devastating event that can be difficult to manage and even more difficult to predict.
The clinical features of acute angle closure are readily observed with ophthalmic examination: extreme intraocular pressure elevation, eye pain, corneal edema, shallow anterior chamber and convex iris bowing.
Lee and colleagues look beyond the clinical by objectively measuring anterior segment features during an acute angle closure attack using anterior segment optical coherence tomography. They found that many of the anterior segment OCT parameters changed in expected ways, consistent with clinical observations (e.g., shallower anterior chamber depth and smaller anterior chamber angle.)
Lens vault, which cannot be appreciated clinically, was shown to increase during an acute angle closure attack. This discovery adds a new dimension to our understanding of what actually precipitates an acute angle closure event, providing a fresh look at an old problem.
This study is a good example of how OCT continues to help redefine what we know about many ocular diseases and its role in developing new treatment strategies.