Ocular ultrasound is a non-invasive diagnostic tool used by ophthalmologists to visualize the internal structures of the eye and the surrounding orbit. This technique employs high-frequency sound waves, typically ranging from 10 to 20 megahertz, which travel through the eye’s tissues and reflect back as echoes. A sophisticated computer system then processes these returning sound waves, converting them into detailed images of the eye’s anatomy. This process allows doctors to assess the health of the eye’s posterior segment, even when the view is obscured by conditions that cause cloudiness within the eye.
Understanding the Ocular Ultrasound Procedure
The procedure is quick, painless, and often performed with the patient’s eyes closed, using a water-based gel applied to the eyelid. The transducer, a small probe, sends sound waves into the eye and captures the returning echoes to create images in real-time. The ocular ultrasound is particularly useful for evaluating the posterior segment when the light path is blocked by an opaque cornea, a dense cataract, or significant bleeding inside the eye.
The two primary types of ocular ultrasound are the A-scan and the B-scan, which provide different kinds of information. The B-scan (Brightness-scan) is the most common diagnostic method, producing a two-dimensional, cross-sectional image of the eye’s structures. The A-scan (Amplitude-scan) uses a single line of ultrasound to provide linear measurements, most often used to accurately measure the eye’s axial length for calculating the power of an intraocular lens before cataract surgery.
Visualizing Retinal and Vitreous Pathologies
Ocular ultrasound is frequently utilized to detect issues affecting the posterior chamber, particularly the retina and the vitreous gel. A major finding is retinal detachment, which appears on the B-scan as a highly reflective, thick, cord-like membrane that remains tethered to the optic nerve head at the back of the eye. This appearance helps distinguish it from other conditions that might mimic it.
The scan can also detect a posterior vitreous detachment (PVD), which is a common age-related event where the vitreous gel separates from the retina. A PVD typically presents as a thin, mobile membrane with a characteristic “swaying seaweed” appearance, moving freely within the eye upon kinetic examination. Vitreous hemorrhage, or bleeding into the gel, is visualized as numerous fine, dot-like echoes that can coalesce over time to form dense, organized membranes.
In cases of inflammation or infection, such as endophthalmitis, the ultrasound may reveal inflammatory debris or exudates within the vitreous cavity. The ability to differentiate between rhegmatogenous (tear-related) and exudative (fluid-related) retinal detachments, or to confirm the absence of a detachment beneath a severe hemorrhage, makes the B-scan an indispensable tool for guiding urgent treatment decisions.
Identifying Internal Ocular Tumors and Masses
The ultrasound serves a specialized function in ocular oncology by helping to characterize and monitor abnormal tissue growth inside the eye. The two-dimensional B-scan provides the tumor’s exact size, shape, and location, which are necessary details for diagnosis and treatment planning. Malignant lesions like choroidal melanoma may exhibit a classic “collar-button” or mushroom shape as they break through the retina, and they typically show low to medium internal reflectivity on the A-scan.
In contrast, benign masses such as choroidal hemangiomas often display a more uniform, high internal reflectivity due to their highly vascular nature. The A-scan is used alongside the B-scan to quantify the tumor’s thickness and to analyze the acoustic properties of the mass, aiding in the differentiation of solid tumors from cystic lesions. Monitoring these tumors over time with repeat scans allows the clinician to track growth or regression following treatments like radiation therapy. The scan is especially useful for evaluating pediatric tumors, such as retinoblastoma, where the tumor’s acoustic characteristics, including the presence of calcification, are important diagnostic markers.
Assessing Acute Trauma and Foreign Objects
In the setting of acute injury, ultrasound is often the fastest and safest method to assess the extent of damage to the eye’s internal structures. When severe swelling or cuts prevent a doctor from examining the eye directly, the B-scan can be performed gently over the closed lid. This rapid assessment is crucial for ruling out a globe rupture, a serious injury that necessitates immediate surgical intervention.
The scan excels at identifying and localizing intraocular foreign bodies (IOFBs), such as metallic fragments or glass shards, which can be highly reflective. The ultrasound’s precision helps the surgeon determine the object’s exact location, size, and relationship to the retina and lens, information that is vital for safe and successful retrieval. Beyond foreign objects, the procedure can quickly detect traumatic complications like a dislocated lens, choroidal detachment, or a post-traumatic vitreous hemorrhage. In some cases of blunt trauma, the ultrasound can even provide information about the surrounding orbit, occasionally revealing fractures of the orbital wall.