Investigations
1st investigations to order
gonioscopy, examination of anterior chamber angle
Test
Definitive test for diagnosing angle closure.
Usually performed at the slit lamp. Both eyes should be investigated; each eye should be numbed prior to evaluation.
Gonioscopy affords a view of the anterior chamber angle of the eye to evaluate angle structures. Special contact lenses (gonioscopy lenses) allow visualisation of the angle using obliquely inclined mirrors.
Gonioscopy should be performed in a relatively dark room, and prior to instilling dilating drugs to rule out eyes susceptible to angle closure.
If angle closure is present, compression (indentation) gonioscopy with a four-mirror or similar lens is particularly helpful to differentiate between appositional (reversible) closure versus synechial (irreversible) angle closure, as well as allow for assessing the extent of peripheral anterior synechiae.
Gonioscopy also detects plateau iris and other specific anatomical configurations.
Chronic angle-closure glaucoma is diagnosed by noting peripheral anterior synechiae on gonioscopy, progressive optic nerve damage, and visual field loss.
Gonioscopy may be therapeutic (in breaking the attack of acute angle closure).
Result
trabecular meshwork is not visible in angle closure, because the peripheral iris is in contact with it
slit-lamp examination
Test
The slit lamp, combined with a high magnification posterior pole lens, is recommended for examining the optic disc.
Optic disc examination, employing slit lamp or funduscopy, may show typical changes of glaucoma, such as a large optic cup and nerve fibre loss.
The anterior chamber depth and size of the phakic (posterior pole) lens should be noted.[1]
Anterior chamber inflammation and iris abnormalities are suggestive of a recent or recurrent attack.
Result
shallow central and peripheral anterior chamber, corneal oedema, lens changes, and corneal endothelial loss; large optic cup and nerve fibre loss may be observed
automatic static perimetry
Test
Identifies the presence and degree of glaucomatous visual field loss during initial diagnosis and subsequently during follow-up care.[1]
Result
visual field defects
Investigations to consider
ultrasound biomicroscopy
Test
Can provide objective documentation of angle closure when gonioscopic findings are unclear (e.g., preclusion by corneal disease or poor patient cooperation).
Useful for demonstrating specific aetiologies for angle closure, such as plateau iris or supraciliary body fluid, and for demonstrating dynamic changes in the angle during light and dark, and after other provocative tests that trigger closure, and after treatment.
Ultrasound biomicroscopy may provide better characterisation of the posterior iris and ciliary body than anterior segment optical coherence tomography, but it is operator dependent and more time consuming.[1]
Result
closed angle; occludability of the angle in the dark versus light; plateau iris or supraciliary body fluid
anterior segment optical coherence tomography (AS-OCT) (of angle)
Test
Can provide objective documentation of angle closure when gonioscopic findings are unclear (e.g., preclusion by corneal disease or poor patient cooperation).
AS-OCT is useful for demonstrating dynamic changes in the angle during light and dark.
Quantitative characteristics include angle opening depth, trabecular-iris space area, angle recess area, iridotrabecular contact index, lens vault, and iris volume.
AS-OCT is less capable of defining specific aetiologies for angle closure because it cannot effectively image structures behind the iris (e.g., the ciliary body).[1]
Result
closed angle; occludability of the angle in the dark versus light
objective quantitative assessment of optic nerve damage
]
Emerging tests
corneal hysteresis
Test
Corneal hysteresis refers to the corneal response to transient compression and release by an air-puff tonometer (i.e., the difference between the initial and rebound applanation pressure). Values may be lower in glaucoma, and lower values may be associated with an increased risk of glaucoma progression.[28]
Interpretation can be affected by other host factors (e.g., surgery, age, axial length, intra-ocular pressure). Where measurement is possible, corneal hysteresis can be used to complement other structural and functional assessments for both the risk of glaucoma and the risk of progression (lower values indicate increased risk). Refer to product literature for reference values.[28][31]
Result
lower values observed in those at risk of diagnosis or progression
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