eye normal
anatomy
anterior chamber
- filled with aqueous humor.
- bordered anteriorly by the cornea
- posteriorly by the iris, lens and ciliary bodies.
posterior chamber
- filled with vitreous humor.
- the sclera is the white outer layer of the eye.
- the choroid is the next layer under the sclera from the optic nerve posteriorly to the ciliary bodies anteriorly.
- the retina is the innermost layer. it is continuous with the optic nerve and extends to the pars plana (the posterior attachment of the ciliary bodies). this junction forms the scalloped ora serrata anteriorly. this is approximately 3/4 of the distance to the anterior chamber.
increase your depth to assess the retro-ocular space.
fan through in longitudinal and transverse.
reduce your depth to better assess the anterior chamber and lens.
increase your depth to assess the retro-ocular space.
fan through in longitudinal and transverse.
ultrasound of the optic nerve sheath diameter (onsd) to assess raised intra-ocular pressure.
measure: 3mm back from the optic disc.
>5mm suggests raised intracranial pressure.
scan protocol
role of ultrasound
- ultrasound is used primarily to assess internal structures of the globe, particularly when direct visualization is obscured by cataracts, haemorrhage or external swelling closing the eye.
- assessment of intra-ocular masses & measurement of tumour thickness for staging.
- differentiating between choroidal or retinal detachments.
- some retro-occular applications.
- relationship of normal anatomy and pathology to each other
limitations
- open wounds
- penetrating foreign bodies
- ruptured globe
- increased intra ocular pressure (iop)
none of these contra-indicate the scan. all of these can be worked around using gentle pressure and sterile gel/standoff pad if required.
patient preparation
- ensure you give the patient a good explanation about the test before you begin. this will include the instructions of what you require from them in regards to asking them look up/down; towards/away from you. that this is always with closed eyes and only their eyes. not turning their head.
- supine position
- eyes closed
- tissues for the patient to hold to wipe their eyes on completion of the scan. this also serves as comfort that they can wipe if they really feel the need to.
equipment setup
use of a high resolution, small footprint probe (10-15mhz) is essential when assessing the internal structures of the globe. good colour / power / doppler capabilities when assessing vessels or vascularity of a structure.
scanning technique
- explain the procedure.
- position the patient supine.
- scan the patient through their closed eyes.
patient instructions:
give the patient some tissues and explain that should they need to open their eyes, to let you know and they can use the tissues to wipe their eye.
- if possible, use sterile gel. apply a small amount of gel to the probe.
- be prepared to change frequency output of probe (or probes) to adequately assess both superficial and deeper structures.
anterior chamber
- reduce the depth to include the posterior aspect of the lens and zoom to fill the screen.
- use thick gel and minimal to no pressure because the anterior chamber is easily compressed.
- sweep in both sagittal and transverse checking for symmetry.
- look for sharp margins where the cornea meets the lateral margins of the iris & ciliary bodies (limbus).
- ensure the lens is intact, anechoic and normally located. a cataract will be seen as echogenic heterogeneity of the lens.
- document the normal anatomy and any pathology found, including measurements and vascularity if indicated.
posterior chamber
- increase the depth to include the entire globe and proximal optic nerve.
- in transverse, ask the patient to look left and right to facilitate maximum scan range.
- similarly, in sagittal, ask the patient to look up/down.
- look for a smooth inner wall (retina) of uniform thickness and echogenicity.
- check for homogeneity of the vitreous humour. commonly in elderly people there will be some echogenic ‘debris’ within the vitreous due to degenerative changes. a vitreous haemorrhage will be seen as mobile, fibrinous, complex material possible tethered.
whilst rare to see pathology, check that the optic nerve is uniform and symmetrical in size bilaterally with no retro-ocular masses. - document the normal anatomy and any pathology found, including measurements and vascularity if indicated.
basic hardcopy imaging
an eye series should include the following minimum images:
- anterior chamber – longitudinal and transverse.
- entire globe: longitudinal-eyes up/down
- entire globe: transverse-eyes left/right
- power doppler of retina
- macula/fovea longitudinal and transverse
- comparison right v’s left
document the normal anatomy. any pathology found in 2 planes, including measurements and any vascularity.