Investigations
1st investigations to order
gonioscopy, examination of anterior chamber angle
Test
Definitive test for diagnosing angle closure.
Gonioscopy of both eyes should be performed on all patients in whom angle closure is suspected.[17] It should also be performed prior to instilling dilating medications 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.
It is also important for the detection of plateau iris and other specific anatomical configurations.
It 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 best method of examining the optic disc is with the slit lamp combined with a high magnification posterior pole lens. The anterior chamber depth should be noted and the size of the phakic lens.[17]
Result
shallow anterior chamber; and signs of glaucoma: corneal oedema, lens changes, and corneal endothelial loss
automatic static perimetry
Test
Identifies the presence, and quantifies the amount, of glaucomatous visual field loss during initial diagnosis and subsequently during follow-up care.
Result
visual field defects
Investigations to consider
ultrasound biomicroscopy
Test
Can be ordered for objective documentation of angle closure when findings during physical examination (gonioscopy) are not clear.
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 and after treatment.
Ultrasound biomicroscopy may provide better characterisation of the posterior iris and ciliary body than anterior segment optical coherence tomography.[17]
Result
closed angle; occludability of the angle in the dark versus light; plateau iris or supraciliary body fluid
anterior segment optical coherence tomography (of angle)
Test
Can be ordered for objective documentation of angle closure when findings during physical examination (gonioscopy) are not clear.[17]
Useful for demonstrating dynamic changes in the angle during light and dark.
Less capable of defining specific aetiologies for angle closure due to inability to image behind the iris.
Result
closed angle; occludability of the angle in the dark versus light
evaluation of the optic nerve head by fundoscopy
Test
The fundus and optic nerve head should ideally be evaluated using a direct ophthalmoscope or slit-lamp biomicroscope with an indirect lens, the central portion of a gonioscopy lens, or via a non-mydriatic camera.[17]
Result
may show typical changes of glaucoma such as a large optic cup and nerve fibre loss
retinal optical coherence tomography
Heidelberg's retinal tomography
Test
Can be used to assess loss of nerve tissue in and around the optic nerve objectively and quantitatively.[32]
Presents this in relation to a nomogram derived from healthy eyes.
Result
quantifies neural tissue in and around the optic nerve
GDx nerve fibre analyser
Test
Can be used to assess loss of nerve tissue in and around the optic nerve objectively and quantitatively.[32]
Result
quantifies neural tissue in and around the optic nerve
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][33]
Result
lower values observed in those at risk of diagnosis or progression
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