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POINT OF CARE ULTRASOUND – OCULAR
Aim
To present common indications for ocular ultrasound (US) in the emergency
department.
Background
Ocular US enables visualisation of the entire globe and optic nerve. It is
especially useful in assessing the posterior segment when there is opacification
of the anterior segment (eg dense cateract, hyphema). Or in the patient with
significant eyelid swelling where visualisation of the posterior chamber is
difficult.
US should be used with caution in patients where pressure on the globe is
contraindicated (eg penetrating trauma).
Indications in the Emergency Department:
1. Trauma:
- Pupillary response to light if too much eyelid swelling
- Lens dislocation
- Retinal detachment
- Optic nerve sheath diameter for increased ICP
2. Visual disturbance
- Retinal detachment
- Posterior vitreous detachment
- Vitreous haemorrhage
- Optic nerve sheath diameter for increased ICP
Anatomy of the eye
Anatomy of the eye
1. Cornea
2. Iris
3. Ciliary body
AC: anterior chamber
PC: posterior chamber: posterior to iris
4. Vitreous
5. retina (yellow) choroid (orange) sclera (grey)
ON: optic nerve
Lens
US image of the eye
1. cornea
2. Anterior chamber
3. Iris
4. lens
5. Vitreos
6. Retina, choroid, sclera
7. Optic nerve
9. Optic disc
Technique
Linear (vascular) probe
Sterile gel
Tegaderm over eyelid to stop conjunctival contamination with gel
Longitudinal (saggital) and Transverse (axial) views
Can also get pt to look to R, L and up and down to better define any pathology:
annotate eye position on screen
Longitudinal
and
Transvere
Tips
The anterior chamber and vitreous should appear black in the normal eye
The lens always sits symmetrically behind the iris (usually has a thin
hyperechoic posterior wall)
Try to get an anatomical view of the globe (as above) and then angle the probe
superiorly and inferiorly in transverse, and from nasal to temporal in
longitudinal to image the entire globe
Have the focus just beneath the area being examined (on the sonosite done by
changing depth to keep the area being examined in the middle of the screen)
Decrease gain to visualise the optic nerve
Increase gain to visualise pathology in the posterior chamber
Pathology
Pupillary response
Place the probe as anteriorly on the eye as possible with the patient looking
down. Aim the probe caudally angling the probe until the iris is seen.
Image from Wiswell J and Bellamkonda-Athmaram V. Sonographic Consensual Pupillary
Reflex. West J Emerg Med. 2012 Dec; 13(6): 524
Shine a light in the contralateral eye and watch for constriction of the pupil.
Lens
The lens is lentiform shaped. It has a hyperechoic wall and a hypoechoic centre.
The anterior wall is usually less well visualised. It lies summetrically behind the
pupil.
Lens dislocation
The lens may be subluxed (still attached in some form to the ciliary body) or
dislocated (not attached to the ciliary body). When dislocated, it will appear as a
lentiform shape with a hyperechoic rim lying somewhere within the vitreous.
A subluxed lens is usually anterior to the vitreous, but is no longer centred
symmetrically behind the iris (see below). The patient should be imaged in
different positions (eg sitting up, log roll) to ensure lens is attached.
Axial view of the globe
a. lens in normal position
b subluxed lens
Dislocated lens sitting in the vitreous
image from http://sonodigest.blogspot.com.au/2015/07/posterior-dislocation-of-ocularlens.html
Cateract
Centre of the lens appears hyperechoic.
Retina
In the normal eye, the retina cannot be distinguished from the choroid/sclera on
US. The retina is attached anteriorly at the ora serrata (curved arrow; see below)
and posteriorly at the optic nerve.
Retinal Detachment
To be confident that the detachment is retina and not vitreous: try to get the
optic nerve in the image so that retinal attachment points can be visualised.
When detached, the retina is seen as a hyperechoic mobile line bulging into the
vitreous with lucent areas superiorly and inferiorly. Anteriorly, the extent of
detachment never extends beyond the ora serrata and posteriorly it is always
attached to the optic nerve.
Extent of retinal detachment
Typical V shaped of complete retinal detachment. Image from
http://www.slredultrasound.com/ImageoftheMonth.html
Smaller retinal detachment. Note the posterior attachment at the optic nerve.
Note: sometimes subretinal haemorrhage may cause small hyperechoic shadows
inferior to the retina.
Studies show that US for retinal detachment has a high level of accuracyi.
Vitreous detachment
Appears similar to a retinal detachment ie hyperechoic mobile line projecting
into the vitreous. However, as there is no attachment to the optic nerve, the line
may pass over the optic disc.
Vitreous Haemorrhage
Hyperechoic shadows are seen within the usually hypoechoic vitreous.
Initially the shadows will be fine and only slightly hyperechoic. You may need to
increase gain to better visualise the haemorrhage.
With organisation into a haematoma, the shadows will become more linear and
more hyperechoic.
a: acute vitreous haemorrhage (note, fine hyperechoic shadows)
b. chronic vitreous haemorrhage.
Raised ICP
Visualise the optic nerve in longitudinal and transverse. Measure the diameter
3mm posterior to the optic disc. Measure in two planes for accuracy.
vertical measurement to 3mm, then measure width of optic nerve
>5mm optic nerve sheath diameter is 100% sensitive to CT diagnosed raised ICP
and 84% sensitive for intracranial pathology secondary to traumaii.
From: Ohle R, McIsaac SM, Woo MY Sonography of the Optic Nerve Sheath Diameter for Detection
of Raised Intracranial Pressure Compared to Computed Tomography. J Ultrasound Med 2015. 34
(34) 1285-1294.
In conclusion
Ocular US has various applications. Many of these conditions are easily detected
on US and studies show high sensitivities and specificities. However, many
conditions require a careful examination of all parts of the eye. The accuracy will
decrease with poor technique.
Unless otherwise stated, all images from private collection or from De La Hoz Polo M, Lluís AT,
Segura OP et al Ocular ultrasonography focused on the posterior eye segment: what radiologists
should know. Insights Imaging (2016) 7:351–364.
i
Vrablik ME, Snead GR, Minnigan HJ, et al The Diagnostic Accuracy of Bedside Ocular Ultrasonography for
the Diagnosis of Retinal Detachment: A Systematic Review and Meta-analysis. Ann Emerg Med 2015; 65 (2):
199-203.
ii
Whitson MR and Mayo PH. Ultrasonography in the emergency department. Crit Care 2016: 227