B-Scan Ultrasound: Seeing Inside Your Eye
Understanding B-Scan Ultrasound
A B-scan ultrasound is a diagnostic imaging test that creates a two-dimensional, cross-sectional picture of the eye and the area behind it (the orbit). The 'B' stands for brightness mode. The test uses high-frequency sound waves, typically around 10 MHz, to produce images on a screen. Structures that reflect sound waves more strongly appear as brighter points on the image.
This test is noninvasive, meaning nothing enters the eye. It does not use radiation. The technology is similar to the ultrasound used during pregnancy, but it is specially designed for the small, delicate structures of the eye.
A small probe is placed gently on the closed eyelid or on the surface of the eye after numbing drops are applied. The probe sends out sound waves that travel through the eye. When these sound waves hit internal structures such as the retina, vitreous gel, or a tumor, they bounce back to the probe. The probe then converts these returning echoes into an electrical signal, which a computer turns into a real-time image.
Different tissues inside the eye reflect sound waves in different ways. This allows a retina specialist to tell the difference between the vitreous (the clear gel filling the eye), the retina, and the choroid (the blood vessel layer beneath the retina). The result is a detailed map of the eye's interior.
B-scan probes come in different frequencies, and each frequency has strengths. A standard 10 MHz probe is ideal for imaging the entire eye, including low-intensity structures like the vitreous gel and small particles floating within it. A higher-frequency 20 MHz probe provides improved resolution for more detailed views but does not penetrate as deeply into the eye.
Ultrasound biomicroscopy (UBM) uses even higher frequencies of 20 to 50 MHz. These probes penetrate only about 5 to 10 millimeters into the eye but produce incredibly detailed images of the front part of the eye (the anterior segment). The choice of probe depends on which part of the eye a retina specialist needs to examine.
Why a B-Scan May Be Needed
A retina specialist normally examines the back of the eye using special lenses and lights during a dilated eye exam. However, certain conditions can block this direct view. A dense cataract (a cloudy lens inside the eye), vitreous hemorrhage (bleeding inside the eye), or corneal scarring can make it impossible to see the retina clearly.
In these situations, a B-scan ultrasound becomes essential. Sound waves pass through cloudy or opaque tissues that light cannot penetrate. This gives the retina specialist the ability to check for serious problems like a detached retina even when the eye cannot be examined in the usual way.
B-scan ultrasound helps diagnose and monitor a wide range of eye conditions. Some of the most common reasons for this test include:
- Retinal detachment: identifying whether the retina has separated from its supporting tissue
- Vitreous hemorrhage: detecting blood inside the eye that blocks the view
- Intraocular tumors: finding and measuring growths such as choroidal melanoma or retinoblastoma
- Vitreous degeneration: evaluating changes in the gel filling the eye
- Eye trauma: assessing damage to the internal structures of the eye after an injury
Some eye conditions look alike on a standard exam, and a B-scan helps tell them apart. For example, the test can differentiate between a retinal detachment caused by a tear in the retina (rhegmatogenous) and one caused by fluid buildup (exudative) or pulling on the retina (tractional). Each type requires a different treatment approach.
B-scan ultrasound can also help distinguish serous (fluid-filled) choroidal detachments from hemorrhagic (blood-filled) ones, differentiate between types of iris and ciliary body lesions, and determine whether swelling of the optic nerve head is caused by buried drusen or a more serious condition like papilledema (swelling from increased pressure in the brain).
For patients with a dense cataract that prevents a clear view of the retina, a B-scan ultrasound may be part of the preoperative evaluation. The test confirms that the retina is healthy and in its proper position before surgery. Finding an unexpected retinal detachment or tumor before cataract surgery can change the entire treatment plan.
Who May Need a B-Scan
Certain conditions increase the likelihood that a B-scan ultrasound will be needed. People with diabetes mellitus face a higher risk of vitreous hemorrhage due to proliferative diabetic retinopathy. In fact, proliferative diabetic retinopathy accounts for approximately 32% of vitreous hemorrhage cases, retinal tears account for about 30%, and proliferative retinopathy after retinal vein occlusion accounts for roughly 11% (PMC, 2017).
Other risk factors include high myopia (severe nearsightedness), which increases the risk of retinal detachment, previous eye surgery or eye trauma, and age-related changes like posterior vitreous detachment (when the vitreous gel separates from the retina).
Spontaneous vitreous hemorrhage occurs in approximately 7 cases per 100,000 people (PMC, 2017). While this may seem uncommon, vitreous hemorrhage in the setting of an acute posterior vitreous detachment has been estimated to be associated with a retinal tear or break in 70% to 95% of cases (PMC, 2017). This high association is why prompt evaluation with B-scan ultrasound is so important when bleeding blocks the view of the retina.
Any person who has experienced significant trauma to the eye may need a B-scan ultrasound. Injuries can cause internal bleeding, retinal detachment, or other damage that is not visible from the outside. The test provides a safe way to assess the full extent of damage without additional risk to the injured eye.
What to Expect During the Test
Little preparation is needed for a B-scan ultrasound. In most cases, the retina specialist or a trained technician will apply numbing eye drops if the probe will touch the surface of the eye. If the scan is performed through the closed eyelid, a water-based gel is applied to the eyelid to help conduct the sound waves. Contact lenses should be removed before the test.
The entire process typically takes only 10 to 15 minutes. There are no dietary restrictions or medication changes needed beforehand.
You will be asked to sit or recline. The technician or retina specialist will gently place the probe on your closed eyelid or on the surface of your eye. You may be asked to look in different directions while the probe is in place. This allows the specialist to capture images of different areas inside the eye.
The test does not cause pain. You may feel light pressure from the probe, and the gel may feel slightly cool. Some patients are asked to keep their eyes still or move them slowly during certain parts of the scan. Real-time images appear on a screen, and the specialist may record still images or video segments for later review.
There is no recovery time after a B-scan ultrasound. You can return to normal activities right away. Your vision will not be affected by the test, though you may need to wipe away the gel used during the procedure. If numbing drops were used, the sensation in your eye will return within a few minutes.
Results are often available immediately. The retina specialist may review the images with you during the same visit and discuss the findings and any next steps.
How Accurate Is B-Scan Ultrasound
B-scan ultrasound has proven to be a highly reliable diagnostic tool. In a study evaluating the reliability of ocular ultrasonography for presurgical evaluation of various vitreoretinal conditions, overall sensitivity was 92.31% and specificity was 98.31% for identification of rhegmatogenous retinal detachment (Medscape). This means the test correctly identifies retinal detachment in the vast majority of cases and very rarely produces a false positive result.
For eyes that have experienced trauma, B-scan ultrasound performs well in identifying the status of the retina. Studies show a sensitivity of 90.9% and specificity of 97.7% for evaluating the retina after eye injuries (Medscape). These high accuracy rates make the test a trusted tool for guiding urgent treatment decisions.
While B-scan ultrasound is highly useful, it does have some limitations. The quality of images depends partly on the skill of the person performing the test. Very small lesions may be difficult to detect, and some conditions may require additional imaging such as optical coherence tomography (OCT) or fluorescein angiography for a complete evaluation. In some complex cases, a retina specialist may use B-scan alongside other tests to build a full picture of what is happening inside the eye.
How B-Scan Results Guide Treatment
One of the most important uses of B-scan ultrasound is helping a retina specialist determine how quickly treatment is needed. If the scan reveals a retinal detachment, urgent surgical intervention is typically recommended to prevent permanent vision loss. If the scan shows a vitreous hemorrhage without retinal detachment, the approach may involve careful monitoring as the blood clears on its own.
For patients with intraocular tumors such as choroidal melanoma, B-scan ultrasound is used to measure the size of the tumor at diagnosis and then monitor it over time. Scans may be performed every three to six months to track any changes in size. Growth of a tumor may signal the need for treatment, while a stable tumor may be safely observed.
When surgery is needed, B-scan ultrasound helps the retina specialist plan the procedure. For example, before a vitrectomy (a surgery to remove the vitreous gel), the scan can reveal the location and extent of bleeding, the presence of scar tissue or membranes, and whether the retina is attached or detached. This information helps the surgeon prepare for what to expect during the operation.
Recent Advances in Ultrasound Technology
Ultrasound technology for the eye continues to improve. The introduction of high-frequency 20 MHz contact probes offers improved resolution for certain applications. These probes are especially useful for examining structures closer to the front of the eye, including the iris and ciliary body. Ultrasound biomicroscopy probes ranging from 20 to 50 MHz provide incredibly detailed images of the anterior segment of the eye.
Modern ultrasound equipment now allows real-time examinations to be stored as still images or video segments. This makes it easier for a retina specialist to compare scans taken at different times and track changes in conditions such as tumor size or the resolution of vitreous hemorrhage. Digital storage also allows images to be transmitted to other specialists for second opinions when needed. Newer devices include automatic scan location detection technology, which helps ensure consistent imaging from one visit to the next.
When to See a Retina Specialist
Certain symptoms require immediate evaluation by a retina specialist or a visit to the emergency room. See a retina specialist or go to the emergency room immediately if you experience any of the following:
- Sudden vision loss in one or both eyes
- A sudden increase in floaters (spots or strands drifting in your vision)
- Flashes of light, especially in your side vision
- A shadow or curtain spreading across part of your visual field
- Sudden eye pain with changes in vision
A retina specialist may recommend a B-scan ultrasound if you have been told that a dense cataract, vitreous hemorrhage, or corneal problem is blocking the view of your retina. The test may also be recommended after eye trauma, if a tumor is suspected, or as part of ongoing monitoring for a known condition. If you have diabetes and are at risk for diabetic eye disease, a B-scan may be needed if bleeding inside the eye develops.
For some patients, B-scan ultrasound becomes part of a regular monitoring schedule. This is especially true for individuals with intraocular tumors, chronic vitreous hemorrhage, or conditions that require ongoing evaluation of structures behind a cataract or other obstruction. Your retina specialist will determine the appropriate frequency of testing based on your specific condition.
Questions and Answers
B-scan ultrasound is considered very safe for nearly all patients. It uses sound waves rather than radiation, so there is no exposure to X-rays or other ionizing energy. The test is safe for children, elderly patients, and individuals with other health conditions. In cases of open globe injury (a wound that penetrates the wall of the eye), the test may be performed with extra caution or through the closed eyelid to avoid putting pressure on the injured eye.
An OCT scan (optical coherence tomography) uses light waves to create extremely detailed images of the retinal layers. It requires a clear line of sight into the eye to work properly. A B-scan ultrasound uses sound waves, which can pass through blood, cataracts, and other opaque materials that block light. The two tests serve different purposes and are often used together. A retina specialist chooses the right test based on what needs to be seen and whether the view into the eye is clear.
Some patients need only a single B-scan to diagnose a condition, while others require repeated scans over weeks or months. For example, a patient with vitreous hemorrhage may have follow-up scans to check whether the blood is clearing and to watch for retinal detachment. Patients with intraocular tumors may have B-scans every three to six months. Your retina specialist will recommend a schedule based on your diagnosis and how the condition is progressing.
A B-scan ultrasound is excellent for detecting many serious conditions, including retinal detachment, vitreous hemorrhage, and intraocular tumors. However, it is not designed to evaluate every eye problem. Conditions affecting only the surface of the eye, the optic nerve pathway to the brain, or very subtle changes in the retinal layers may require different tests. A retina specialist may combine B-scan findings with results from other imaging tests to reach a complete diagnosis.
The B-scan itself does not require any follow-up care. You can drive home, return to work, and resume all normal activities immediately. However, the findings from the scan may lead to additional appointments, further testing, or treatment. If the scan reveals an urgent condition like a retinal detachment, your retina specialist will discuss next steps with you right away.