Ophthalmic ultrasonography gained popularity in the 1970s and is currently among the most useful diagnostic tools clinicians use to evaluate intraocular and orbital health—particularly in the presence of opaque and sight-limiting media.1
The use of pulse-echo technology from a handheld transducer probe emits high-frequency sound waves as the probe makes direct contact with the eyelid or scleral using a sound-coupling agent, such as 2.5% methylcellulose.
The echoes are processed and displayed in real-time on computer monitors for evaluation. Imaging occurs rapidly, at approximately 1,000 frames per second, allowing the motion of the vitreous and globe to be detected with ease.1
How ultrasonography works and how to use it
The ultrasound probe is a mobile handheld device that the clinician gently places in direct contact with the eyelid or sclera using a sound coupling agent (i.e., 2.5% methylcellulose).
The clinician then systematically moves the probe along the transverse, axial, and longitudinal meridians to image and examine intraocular and orbital structures. The two modes of display when using an ultrasound are amplitude scan (A-scan) or brightness scan (B-scan).
The differences between A-scan and B-scan ultrasonography
The A-scan employs the tear film as the coupling agent sends a single sound beam from the transducer probe through the eye.
The echoes that return are plotted in an image that represents the following landmark structures in the eye:
- Cornea
- Anterior lens
- Posterior lens
- Retina
- Sclera
- Orbital tissue
Figure 1 represents an A-scan; from left to right, the spikes correspond to the cornea, anterior lens, posterior lens, retina, sclera, and orbital tissue.
Figure 1: Courtesy of Inrava Khasnabish, OD, FAAO.
The B-scan requires a coupling agent, such as 2.5% methylcellulose, and emits a series of soundwaves at a frequency of 10MHz to 12MHz. The echoes that return are converted to dots with variable amounts of brightness and intensity.
High-intensity echoes result from acoustically denser tissue and are hyperechoic and appear white, while low-intensity echoes are hypoechoic and appear in varying shades of gray. The absence of echoes is anechoic and appears black.
The landmark structures in the eye on a B-scan are as follows:
- Lens
- Vitreous
- Retina
- Sclera
- Optic nerve
Figure 2 represents a B-scan labeled with major landmarks.
Figure 2: Courtesy of Inrava Khasnabish, OD, FAAO.
Diagnostic abilities of B-scan ultrasonography
Ultrasonography has a plethora of capabilities, however, for this discussion, we will hone in on the use of the B-scan. The B-scan provides visualization of ocular structures when direct visualization is not possible due to media and/or structural anomalies.
When intraocular structures can be seen, the use of the B-scan allows clinicians to differentiate ocular findings that may otherwise appear similarly on other modes of ancillary imaging.
Table 1 lists examples of when B-scan ultrasonography can detect intraocular structures.
| Unable to See Intraocular Structures | Able to See Intraocular Structures |
|---|---|
| Evaluating retinal health in the presence of dense ocular media (i.e., corneal scar, mature cataract, hyphema/hypopyon, vitreous hemorrhage/opacity, trauma) | Identifying iris vs. ciliary body lesions |
| Evaluating retinal health in the presence of eyelid anomalies preventing opening of the eye | Identifying types of intraocular tumors (choroidal melanoma vs. choroidal hemangioma) |
| Corneal irregularities that prevent visualization of intraocular structures | Evaluate the posterior scleral and anterior orbit for inflammation in posterior scleritis |
| Identify the type and location of intraocular foreign bodies (metal/glass have specific echo shadows vs. wood/organic matter have variable echo) | Identifying types of retinal detachments (tractional vs. rhegmatogenous vs. serous) |
| Identifying optic disc drusen/buried drusen vs. true disc edema |
Table 1: Courtesy of Inrava Khasnabish, OD, FAAO.
B-scan images are displayed horizontally, which means the area closest to the probe will be on the left side of the image, and the areas furthest from the probe will be on the right side of the image. When interpreting, B-scans focus on identifying major anatomical landmarks (i.e., lens, vitreous retina, sclera, optic nerve) to determine anomalies that may correspond with pathology.
Vitreous cavity characteristics on B-scan imaging
When evaluating the vitreous cavity on a B-scan, a healthy vitreous will appear echolucent or anechoic (absence of echoes) and appear black when imaged.
In the event of vitreous degeneration, posterior vitreous detachment, vitreous hemorrhage, asteroid hyalosis—each shown respectively in the figures below—and/or other findings in the vitreous cavity, they will appear with low-intensity echoes that are hyperreflective when imaged.
Figure 3 reveals vitreous degeneration on B-scan ultrasonography.
Figure 3: Courtesy of Inrava Khasnabish, OD, FAAO.
Figure 4 illustrates posterior vitreous detachment on B-scan ultrasonography.
Figure 4: Courtesy of Inrava Khasnabish, OD, FAAO.
Figure 5 shows vitreous hemorrhage on B-scan ultrasonography.
Figure 5: Courtesy of Inrava Khasnabish, OD, FAAO.
Figure 6 illustrates asteroid hyalosis on B-scan ultrasonography.
Figure 6: Courtesy of Inrava Khasnabish, OD, FAAO.
The value of retinal B-scans
B-scans are particularly instrumental in evaluating the retina for tears and detachments. When evaluating the retina tractional, rhegmatogenous and serous retinal detachments will appear differently on a B-scan.
A tractional detachment will have a smooth concave surface with minimal movement, however, it may adopt a funnel-shaped configuration on a dynamic B-scan, as seen in Figure 7.
Figure 7 shows dynamic B-scan ultrasonography of a tractional detachment, with a characteristic funnel configuration.
Figure 7: Courtesy of Tapuwa Chikwinya OD, MBA, FAAO.
Figure 8 highlights a rhegmatogenous detachment, and demonstrates the corrugated appearance that undulates on a dynamic B-scan.
Figure 8: Courtesy of Roman Polishchuk, OD.
Figure 9 illustrates how, on a dynamic B-scan, a serous detachment will have a smooth retinal surface with fluid shifting as the patient moves their eye.
Figure 9: Courtesy of Roman Polishchuk, OD.
The choroid and B-scan ultrasonography
The choroid appears as a thicker layer than the retina on a B-scan. When distinguishing choroidal nevi from melanomas there are several hallmark differences to note; melanomas are smooth, dome-shaped, and have low to medium internal reflectivity, as seen in Figure 10, below.
Figure 10 highlights B-scan ultrasonography of choroidal melanoma.
Figure 10: Courtesy of Inrava Khasnabish, OD, FAAO.
Choroidal nevi are typically flat, with minimal reflectivity on B-scan. Tumors that have broken Bruch’s membrane will appear with a collar-button or mushroom-shaped lesion on B-scan images.
B-scan ultrasonography of the optic nerve
An ultrasound of the optic nerve is primarily used to determine the cause of a swollen optic nerve on a fundus exam. On a B-scan, true papilledema will present with a widened optic nerve.
Alternatively, optic disc drusen, which mimics the funduscopic presentation of papilledema, will reveal a highly reflective area found at the base of the optic nerve head when the drusen is calcified (Figure 11). Tumors of the optic nerve head, including gliomas and meningiomas can also be differentiated on a B-scan as they present with variable reflectivity.
In Figure 11, observe the refractile deposit at the base of the optic nerve head of the optic disc drusen.
Figure 11: Courtesy of Roman Polishchuk, OD.
Pearls for successful B-scan imaging
When performing B-scan imaging, proper directions for the patient are imperative. It is helpful to instruct the patient on what they will feel (cold gel on their eyelid and light pressure), in addition to where they should maintain their gaze during the test.
When the patient knows where to look and is not continuously moving, the quality of the images recorded is improved immensely. The clinician should work to maintain the probe perpendicular to the tissue being imaged for the best resolution possible.
The center of the image has the highest quality and best resolution, for this reason, the clinician should aim to center any points of interest on the scans.
Incorporating B-scan imaging into clinical workflows
In a busy office, there are a number of techniques that can be used to triage and determine when ancillary testing should be performed. With the B-scan, the mobile probe can be set up in any exam lane and prepared by the technician; most modern B-scans are mobile, however, some units are fixed.
This mobility and ease of imaging allow clinicians to determine whether this additional test is necessary during pre-testing and clinical examination. For longstanding findings, or retinal findings that are being monitored on a serial basis, clinicians can notate for the B-scan to be performed at subsequent visits—thereby increasing efficiency and reducing chair time.
Additionally, the compact and mobile nature of the B-scan probe allows for the use of it for bed bound patients, which is particularly impactful when no other methods are available to evaluate retinal integrity.
Coding/billing and insurance considerations for B-scan imaging
When billing a B-scan, it is imperative to include a modifier to identify the eye that was examined, as the Current Procedural Terminology (CPT) code 76512 is not a bilateral code. Modifiers typically used are RT/LT or 50 to indicate bilateral examination. The modifier 26 should only be used if you are interpreting the test, but did not perform it in the office.
This is among the highest reimbursed CPT codes for ophthalmic diagnostic imaging. Depending upon the medical insurance, reimbursement per eye can range between $45 and $250.
This code can be billed with most other CPT codes, including but not limited to:
- 92250
- 92134
- 92133
- 92132
- 92025
- 92020
- 92202
Other procedure codes local to the anterior segment or otherwise can also be billed simultaneously. The International Classification of Diseases, Tenth Revision (ICD-10) codes commonly billed with CPT 76512 must relate to vitreous or retinal findings, most commonly including all the H43 and H44 codes.
An exhaustive list of ICD-10 codes that are approved for CPT 76512 can be found on the American Academy of Ophthalmology’s website.6
Conclusion
The B-scan ultrasound is a compact and versatile tool in the world of eyecare. As a painless procedure, through the use of soundwaves ranging from 10 to 12MHz, an image of intraocular structures can be visualized.
This tool allows the visualization of structures not only when fundoscopy is limited, but also when funduscopic ambiguity is present. The small but powerful tool can be seamlessly integrated into a busy office, especially the more modern and mobile units, which allow for efficiency during clinical examination.
With medical reimbursement ranging from $45 to $250 per eye with minimal limitations when performing other ancillary tests simultaneously, the B-scan ultrasound is a small yet mighty tool for every clinician to keep handy.
As with any clinical tests, practice makes perfect, and increases speed and accuracy of both performing and interpreting the results.
