OD News Articles

2nd April 2018

Shades of Gray: A Guide to Ultrasonography

by Jennifer Ramey, OD Lewiston, ID

Inevitably, there comes a day when a patient walks in with a condition that prevents visualization of the eye’s internal structures. Whether it’s a cloudy cornea, dense cataract, vitreous hemorrhage, or simply anatomy blocking the view, a quick ultrasound will clear the air—and make pathology more discernible. While neither B-scan or UBM are new technologies, join me for a quick review to help distinguish the black from white.

The Aviso scanning instrument

B-Scan

Used in eye care since the 1950s, B-scan technology images the posterior segment (namely the lens, vitreous, retina, choroid, sclera, and orbit) when direct visualization is obscured on traditional slit-lamp biomicroscopy. It uses high frequency sound waves (10–20 MHz) that are transmitted by probe into the eye. Then, the waves are echoed back to the probe and converted by electrical signal into a two-dimensional, gray-scale image. Transmission occurs about a thousand times per second, producing a real-time video for dynamic evaluation. Different probe orientations can help determine laterality, elevation, and length of lesions.

    Normal B-scan
    Normal B-scan
Probe Orientations

Transverse

  • Determines laterality
  • Oriented tangential to limbus (superior for vertical scans, nasal for horizontal scans)
  • Meridian designated by clock hour in center of the scan

Longitudinal

  • Determines length of lesion (anterior to posterior)
  • Oriented perpendicular to limbus (marker to center of scan)
  • Meridian designated by clock hour opposite of probe marker

Axial

  • Determines location of lesions to anatomical markers
  • Probe is placed on center of cornea with patient gaze straight ahead
  • Can be performed horizontally, vertically, or obliquely
Indications
  • Corneal opacity
  • Hyphema
  • Miosis
  • Dense Cataracts
  • Vitreous Opacity
Protocol
  1. Disinfect the probe.
  2. Seat the patient comfortably, upright or reclined, with head secured.
  3. Instill one drop of topical anesthetic in each eye. I do this even if I only place the probe on the eyelids.
  4. Apply a coupling agent, such as artificial tear gel or 2.5% methylcellulose, to the probe tip.
  5. Place the probe gently on the patient’s eyelid, cornea, or conjunctiva, and scan through the different meridians. Directing gaze away from the probe to the meridian being scanned will allow for clear transmission, avoiding the dense natural lens.
  6. Save and/or print your images. It’s a beautiful baby girl, I croon to coax out a laugh and lighten the mood.
Gain Control

The gain control knob adjusts the amplification of the signal, not the energy transmitted. Lowering the gain improves resolution, though lowers depth penetration, allowing only the strongest echoes (eg. disc drusen, retina, and sclera) to remain. A higher gain will allow weaker echoes (eg. vitreous opacities) to show.

Interpretation

Knowing what normal looks like will help in evaluation of pathology. The stronger the echo, the brighter the display will be. Dense structures (vitreous crystals, blood, tumors, and choroid) look whiter. Clear structures (unclouded lens, vitreous gel, serous detachments) appear dark or black. It is also helpful to remember that the top part of the scan corresponds to the location of the probe marker.

    Pathology on B-scan

    Four views of pathology on B-scan
    A: Vitreous hemorrhage. B: Choroidal melanoma with overlying retinal detachment. C: Ciliary body tumor. D: Optic disc drusen.

Vitreous—A young, healthy vitreous will be echo-lucent or dark. Syneresis will be reflective, and vitreous hemorrhages will be more reflective and can settle inferiorly due to gravity. Calcium deposits (asteroid hyalosis) and metallic foreign bodies will show as hyper-reflective pinpoints.

Retina—Retinal tears, flaps, and detachments can be differentiated using B-scan. The retina will be a highlyreflective membrane; if detached, this can undulate when viewed dynamically. Serous detachments will show an underlying dark area. Retinoschisis, when viewed dynamically, will image as a rigid dome.

Choroid—This appears much thicker than the retina on B-scan. A choroidal detachment will show as a dome shape. They are often hemorrhagic resulting in an underlying medium-reflective gray area. Choroidal melanomas and nevi can be differentiated on B-scan. Melanomas will show dome-shaped elevation with low reflectivity and internal vascularity, while a nevus will be highly reflective without internal vascularity.

Optic Nerve—Papilledema can be distinguished from buried disc drusen using B-scan. Papilledema will result in a widened nerve, while drusen will appear as hyper-reflective foci.

Ultrasound Biomicroscopy (UBM)

UBM technology became available in the 1990s and uses much higher frequency sound waves (50 MHz) than B-scan. It provides high resolution imaging of the anterior segment—namely the cornea, anterior chamber, iris, lens, and ciliary body. These sound waves are also transmitted by a probe into the eye to create an image. With increased frequency, the sound wave penetration area is lower making UBM ideal for anterior ocular pathology.

Indications

Corneal evaluation:

  • Scars and edema
  • Keratoconus
  • LASIK flap
    Normal UBM scan
    Normal UBM scan

In-depth angle analysis:

  • Angle recession
  • Angle closure
  • Cyclodialysis

Natural or pseudophakic lens positioning:

  • Malpositioning vs. capsular bag fixation vs. sulcus fixation

Iris configuration and lesions:

  • Discerning pupillary block vs. plateau iris
  • Iris cysts and tumors

Ciliary body evaluation:

  • Cysts and tumors

    Pathology on UBM

    Four views of pathology on UBM
    A: Narrow angle. B: Iris cysts. C: Peripheral anterior synechia. D: Ciliary body tumor.
Protocol
  1. Disinfect the probe.
  2. Seat the patient in a supine position with head secured.
  3. Instill one drop of topical anesthetic in each eye.
  4. Separate the eyelids and place the eye cup on the patient’s globe, centering the cornea.
  5. Create a water bath using a coupling agent, such as saline or 1–2.5% methylcellulose.
  6. Immerse the probe in the water bath approximately 2mm from the cornea with the probe perpendicular to the surface.
  7. Begin the scan. A steady hand will result in a clearer image.
  8. Save and/or print your images. Release the flood gates, I say to prepare patients for the spillover as the eye cup is removed.
Interpretation

Again, recognizing normal will sharpen your pathology skills. Like B-scan, dense structures (iris, sclera, blood, or tumors) provide a more reflective signal or white display. Dark areas represent clear structures (anterior and posterior chambers, lens, or cysts).

Angle Analysis—UBM is great for glaucoma management and can image the angle to determine occludability. It is also helpful for evaluating iris configurations—plateau iris, pupillary block, angle closure, peripheral anterior synechia, iridodialysis, and angle recession.

Iris Lesions—An iris lesion, perhaps nevus vs. cyst, can be difficult to assess on a slit-lamp. But iris cysts will be round and fluid filled (echolucent and dark) on UBM.

Ciliary Body Pathology—Difficult to view on slit-lamp exams, the ciliary body is easily imaged with UBM. A lesion can be measured and monitored on UBM to determine malignancy risk factors.

Optic Nerve—Papilledema can be distinguished from buried disc drusen using B-scan. Papilledema will result in a widened nerve, while drusen will appear as hyper-reflective foci.

Conclusion

Next time your diagnosis lies in the gray area and you aren’t quite sure of the exact pathology, dust off the B-scan or UBM and quickly determine the black from the white. And if you ever have questions, feel free to contact any of our optometric physicians. We’re always happy to help.

Reference

Chiu, S. e. (2016, August 12). Ultrasound Biomicroscopy. Retrieved from EyeWiki: http://eyewiki.aao.org/Ultrasound_Biomicroscopy

He, M. e. (2012). Overview of Ultrasound Biomicroscopy. Journal of Current Glaucoma Practice, 25–53

Ishikawa, H. e. (2004). Anterior segment imaging: ultrasound biomicroscopy. Ophthalmology Clinics of North America, 7–20

Patwardhan, S. e. (2007). Clinical Applications of Ultrasound Biomicroscopy in Glaucoma. Journal of Current Glaucoma Practice, 30–41

Shlensky, D. e. (2015, April 2). Ophthalmologic Ultrasound. Retrieved from EyeWiki: http://eyewiki.aao.org/Ophthalmologic_Ultrasound

Urban, D. e. (2016). Scoring an A+ on a B-Scan. Review of Optometry, 64–71