Background

Ocular ultrasound, specifically B-scan ultrasound, is a non-invasive imaging technique used to evaluate and visualize the internal structures of the eye. This imaging modality plays a crucial role in the assessment of various ocular conditions, providing detailed cross-sectional images that aid in diagnosis and treatment planning. 

B-scan ultrasound utilizes high-frequency sound waves that are emitted from a transducer probe placed on the eyelid or directly on the eye’s surface after applying a coupling gel. These sound waves travel through the ocular tissues, reflecting off different structures within the eye. The echoes produced by these reflections are captured and translated into real-time, two-dimensional images displayed on a monitor. 

The versatility of B-scan ultrasound allows for the evaluation of ocular structures that are not easily visualized through conventional methods, such as the retina, vitreous, lens, optic nerve, and orbit. It is particularly valuable in cases where optical media are opaque due to conditions like cataracts or hemorrhage, providing valuable diagnostic information. 

Indications

Opaque Media: When the structures within the eye cannot be visualized clearly due to opacities such as dense cataracts, vitreous hemorrhage, corneal opacities, or other ocular conditions obstructing direct visualization. 

Evaluation of Posterior Segment: To assess the posterior segment of the eye including the retina, choroid, optic nerve, and vitreous when direct examination is not feasible due to ocular conditions like severe intraocular inflammation, vitreous hemorrhage, retinal detachment, or tumors. 

Assessment of Intraocular Tumors: B-scan ultrasound can aid in the evaluation and characterization of intraocular tumors, such as choroidal melanomas or retinoblastomas. 

Identification of Retinal Detachments: It helps in diagnosing and determining the extent of retinal detachments, whether rhegmatogenous, tractional, or exudative, by visualizing the separation of the retina from the underlying layers. 

Trauma Evaluation: B-scan ultrasound can be used to assess the extent and nature of ocular trauma, including identifying foreign bodies within the eye or assessing the integrity of the globe in cases of suspected ruptures. 

Contraindications

Ocular trauma: In cases of recent ocular trauma, particularly open globe injuries, performing an ultrasound may not be advisable without proper evaluation by an ophthalmologist. Ultrasonography might further exacerbate the injury or cause discomfort. 

Severe eye infections: Conditions such as acute endophthalmitis or severe infectious keratitis might be contraindications due to the risk of spreading infection or causing discomfort to the patient. 

Severe eye inflammation: Ocular conditions associated with severe inflammation, such as acute uveitis or iridocyclitis, may pose challenges in obtaining accurate and clear images due to the inflammatory changes within the eye. 

Allergy to ultrasound gel: The ultrasound gel used as a coupling agent might cause allergic reactions in some individuals. It’s essential to inquire about any known allergies before applying the gel. 

Outcomes

Equipment

Gel or Coupling Medium 

Ultrasound Machine/Scanner 

Linear ultrasound probe 

Patient position

The patient has the option of lying down on an examination table in a supine position or sitting in a recliner chair.  

The choice of position depends on the patient’s comfort and the equipment setup available in the clinic or hospital. 

TECHNIQUE

Step-1: Anchor the probe: 

Using enough gel is crucial, alongside ensuring proper anchoring of the probe to minimize the pressure exerted on the eyes of the patient. 

Hold the linear probe firmly and place your fingers on a bony area of the patient’s face for stabilization. 

To position the Right eye, stabilize your right pinky finger on the nose of the patient as an anchor point. 

Place your right palm or pinky finger on the zygomatic arch to support the left eye. 

Step-2: Obtain transverse view: 

Gently position the probe on the gel that covers the eye of the patient, ensuring that the probe indicator is directed towards the patient’s right side to acquire a transverse view. 

Subsequently, request the individual to shift their gaze both right & left to assess their extraocular movements. This assessment proves crucial particularly in cases where patients experience significant swelling around the eyes due to facial trauma. 

Step-3: Obtain Sagittal View: 

Subsequently, rotate the probe 90° in a clockwise direction, aligning the indicator to face superiorly towards the head of the patient to acquire a sagittal view. Proceed to recognize and locate the identical structures observed in the transverse view. 

When examining the sagittal view, one should observe the vertical movements of the eye, focusing on both superior (upward) and inferior (downward) motions. 

Step-4: Measure ONSD (optic nerve sheath diameter): 

The key marker for detecting elevated intracranial pressure is the assessment of the optic nerve sheath diameter. 

Rotate the probe approximately 10 to 15° laterally in a cross-sectional perspective to observe the direction in which the hypoechoic optic nerve extends away from the base of the eye. 

Note: If the ocular nerve isn’t immediately visible, adjust the probe’s angle upwards and downwards until it becomes visible. 

After obtaining a clear perspective, pause or capture the image. 

Laboratory Tests

Visual Acuity Test: This is a standard test to measure the sharpness of vision.  

Intraocular Pressure Measurement: Often measured using tonometry, this test evaluates the pressure inside the eye. Elevated intraocular pressure can be indicative of conditions like glaucoma. 

Fluorescein Angiography: To perform this test, a dye is injected into an arm vein, where it then makes its way to the blood vessels in the retina. A series of photographs are then taken to evaluate blood flow and detect any abnormalities or blockages in the blood vessels. 

complications

Discomfort: During the procedure, the ultrasound probe might cause mild discomfort or pressure on the eye. However, it’s generally well-tolerated by most patients. 

Inability to Visualize Certain Structures: In some cases, due to the patient’s anatomy or eye conditions, certain structures may be difficult to visualize clearly or might be obscured by other ocular abnormalities. This limitation can affect the accuracy of the imaging. 

Rare Risk of Injury: Though extremely rare, there is a minimal risk of injury to the eye during the procedure, such as corneal abrasions or intraocular bleeding. This risk is usually mitigated by the expertise of the technician performing the ultrasound. 

References

Pictorial essay: B-scan ultrasonography in ocular abnormalities – PMC (nih.gov) 

References

Pictorial essay: B-scan ultrasonography in ocular abnormalities – PMC (nih.gov)