How Do You Do an Ocular Ultrasound?

Step 1: Anchor the probe

Along with a generous amount of gel, anchor the probe to reduce the amount of pressure exerted to the patient’s eyes.

• Grasp the linear probe and place the fingertips on the patient's bony surface.
• The next example assumes that the subject is being scanned using the right hand.
• Anchor the right pinky finger on the patient's nose for the right eye.
• Anchor the right pinky finger or palm on the zygomatic arch (the bony arch at the outer border of the eye socket) for the left eye.

Step 2: Obtain transverse view

• To achieve a transverse view, place the probe lightly on the gel covering the patient's eye, with the probe indication pointing to the patient's right.
• From anterior to posterior, identify the following ocular ultrasound anatomy:
  • Eyelid
  • Anterior chamber
  • Lens
  • Iris
  • Vitreous body
  • Retina
  • Optic nerve

Examine extraocular movements:

• Instruct the patient to look left and right to check for their eye movements. 
• This is crucial if the patient has substantial periorbital edema (swelling around the eye) as a result of facial trauma.
• Gradually, increase the amplitude to identify ophthalmic disorders such as:
  • Retinal detachment
  • Posterior vitreous detachment
  • Vitreous hemorrhage

Step 3: Obtain sagittal view

To achieve a sagittal image, spin the probe 90° clockwise so that the indicator points superiorly toward the patient's head. Identify the structures that are discovered in the transverse view.

Sagittal view of an ocular ultrasound:

• Ask the patient to look up and down while gradually increasing the amplitude to check for
  • Symmetric extraocular muscle movements.
  • Rule out intraocular pathology.

Step 4: Measure optic nerve sheath diameter (ONSD)

• ONSD is a critical parameter that can be used to detect high intracranial pressure (pressure of the cerebrospinal fluid in and around the brain).
• Move the probe about 10° to 15° laterally in the transverse view to examine the optic nerve and measure its diameter.

Ocular ultrasonography, commonly known as ocular echography, is a type of diagnostic imaging technique. Ocular ultrasound is a rapid, painless, non-invasive examination. It is a quick and easy procedure that can be used bedside to examine structural integrity and diagnose any eye pathology or ophthalmologic emergencies.

Ocular ultrasonography can provide information that is not easily available by direct eye examination.

Ocular ultrasound is a technology that is similar to other types of ultrasound. It generates an image by using reflected sound waves and evaluates those images.

Ocular ultrasound may be done in case of the following:

• Vision loss
• Ocular trauma
• Headache
• Increased intracranial pressure

Ocular ultrasound is of two types that include:

1. A-scan:
   • The A-scan, a short form for amplitude scan, measures the length of the eye (axial length).
   • This is a one-dimensional scan.
   • A horizontal axial view shows the optic nerve and macula (the central part of the light-sensitive layer in the eye or retina).
   • This aids in determining the best lens implant for cataract surgery.
   • The patient is allowed to sit upright in a chair and their chin is rested and is asked to look straight ahead.
   • Anesthetic eye drops are instilled in the patient’s eye.
   • A lubricated probe will be put against the front area of the patient’s eye, and it is scanned thoroughly.
   • The patient may be asked to move the eyeball in different directions to improve their view.
   • Alternatively, if the patient is lying down, a fluid-filled cup or water bath is put on the surface of the eye while it's being scanned.
2. B-scan:
   • The B-scan allows to see the space behind the eye and evaluate the following:
     • Retina
     • Retinal detachments
     • Vitreous choroidal masses
     • Tumors
     • Nevi
   • This is a three-dimensional scan.
   • Cataracts and other disorders make it difficult to see the rear of the eye through direct visualization.
   • During a B-scan, the patient’s eyes are closed, and gel is applied to the eyelids.
   • The patient is instructed to move the eyes in various directions while an ultrasound probe is placed against the eyelids.

Seven ocular anomalies shown on ultrasound include:

1. Globe rupture:
   • It is painful vision loss following a high-impact blunt or penetrating trauma.
   • On physical examination, pupil distortion, vitreous fluid extrusion, and internal structure prolapse are seen.
   • Findings on an ocular ultrasound include:
     • Decrease in size of the globe
     • Anterior chamber collapse
     • Vitreous hemorrhage
     • Disruption of normal globe architecture
2. Foreign body:
   • Asymptomatic foreign bodies can cause permanent visual loss, so all patients should be checked carefully.
   • Ocular ultrasound shows shadow or comet tail artifacts that may be produced by a hyperechoic object.
   • Twinkle artifact is seen with color doppler.
3. Retinal detachment:
   • With dynamic scans, retinal detachments display a characteristic wavy movement of the retina.
   • The retina travels at a slower rate than the posterior hyaloid and has higher reflectivity.
   • An ultrasound can be used to determine where the retina has detached using axial, transverse, and longitudinal views.
4. Vitreous hemorrhage:
   • Vitreous hemorrhages are frequently found in the context of abrupt visual loss in one eye.
   • They can occur in diabetic retinopathy and nearly every other retinal neovascular disease.
5. Choroidal nevus:
   • Choroidal nevi can be distinguished from choroidal melanoma by their uniform, high internal reflectivity.
6. Choroidal melanoma:
   • Because choroidal melanomas are more vascular, they have low to medium internal reflectivity.
7. Choroidal hemangioma:
   • Choroidal hemangiomas have a high internal reflectivity that is consistent.

• Indications:
  • Best lens implant before cataract surgery
  • Possible foreign body in the eye
  • Condition of the globe following a trauma
  • Pathologies of the posterior segment caused by opaque media, such as a thick cataract or bleeding in the eye
  • Glaucoma
  • Dislocation of the lens
  • Detachment of the retina
  • Tumors
  • Fixed non-dilating pupil, as in uveitis
  • Corneal opacities
  • Opacities in the vitreous 
• Ocular ultrasound helps determine the following:
  • Reasons for reduced or lost vision
  • Nature of an eye tumor or optic disc lesion
  • Type of retinal detachment
  • Intraocular foreign body detection and localization
  • Orbital lesions
  • Retina, choroid, and sclera in various illnesses, including inflammatory diseases
• Contraindications:
  • Contraindications for an ocular ultrasound are uncommon.
  • The main contraindication is suspected ocular globe rupture in patients with trauma or who have recently undergone surgery because it may result in ocular contents expulsion.