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| INSTRUMENT CORNER |
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| Year : 2018 | Volume
: 30
| Issue : 3 | Page : 216-218 |
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Ultrasound biomicroscopy: An overview
K Girija, VK Smitha, Akshaya Ashok
Little Flower Hospital and Research Centre, Angamaly, Kerala, India
| Date of Web Publication | 17-Dec-2018 |
Correspondence Address:
K Girija
Department of Opthalmology, Little Flower Hospital and Research Centre, Angamaly - 683 572, Kerala
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/kjo.kjo_95_18
How to cite this article:
Girija K, Smitha V K, Ashok A. Ultrasound biomicroscopy: An overview. Kerala J Ophthalmol 2018;30:216-8 |
| Introduction | |  |
Ultrasound biomicroscopy (UBM) is a noninvasive technique used to visualize the structural details of anterior segment of the eye, using a high-frequency ultrasound transducer. The device which was first introduced by Dr. Charles Pavlin and Prof. Stuart Foster in 1989 provides detailed two-dimensional grayscale images of the various anterior segment structures, making it ideal to visualize and evaluate the entire anterior segment.[1]
| Principle | | |
UBM is performed using 35–50 MHz probe, which has a lateral resolution of 50 μ, axial resolution of 25 μ, and depth of penetration of 4–5 mm. Although the image resolution provided by UBM is much higher, its depth of penetration is not as high as a conventional B-scan ultrasonography, making it unsuitable to visualize deeper structures of the eye.
| Parts of Ultrasound Biomicroscopy | | |
- Ultrasound transducer and probe: The probe which is small and light is either handheld or mounted on a gantry [Figure 1]
- Computer monitor with the main processing unit: Records real-time images displayed on the monitor, for later analysis [Figure 2].
| Normal Anatomy | | |
The Bowman's membrane is the first identifiable echo dense structure, followed by the low irregularly reflective stroma. Descemet's membrane appears as a dense highly reflective line. The dark echo-free area behind the cornea is the anterior chamber, the depth of which can be measured from the posterior surface of cornea to the anterior surface of the lens. The angle structures, namely, iris, ciliary body, and scleral spur, can be identified easily on UBM, with the scleral spur being the only constant landmark aiding in the analysis of abnormalities in angle structures [Figure 3].[2] | Figure 3: Normal anatomy of anterior chamber on ultrasound biomicroscopy
Click here to view |
The scleral spur is identified as the anterior-most point of the demarcation line between the ciliary body and sclera, visualized on a longitudinal scan across the limbus. It is typically used as a reference point for measuring parameters such as iris area and volume, angle opening distance, angle recess area, sclera thickness, and trabecular meshwork-ciliary process distance.
| Technique | | |
The examination is done with the patient in the supine position [Figure 4]. After applying topical anesthetic to the eye, an eyecup (plastic or silicone) is placed within the palpebral fissure to create a small water bath. Either methylcellulose solution (1% or 2%) or saline is used as the coupling fluid. The water bath designed by Kapetansky is a flexible polysiloxane cup with a beveled inner edge, providing a watertight seal and using saline as a coupling fluid.[3] The transducer should be placed within the coupling solution in such a way that the scanning beam strikes the target perpendicularly, taking care not to apply undue pressure on the eyecup. The transducer detects the signals reflected from the anterior chamber structures [Figure 4].
While performing a quantitative assessment of the anterior chamber, the room illumination, fixation, and accommodative effort of the patient should be held constant.
| Indications | | |
- In cases of glaucoma, for better understanding of the mechanism of the disease, thereby allowing better treatment directed at the underlying pathophysiology. UBM helps detect pupillary block glaucoma, plateau iris configuration, lens-related angle closure, malignant glaucoma, and pigment dispersion syndrome [Figure 5][2]
- In case of uveitis to detect the presence of cyclitic membranes, supraciliary effusion, ciliary body detachments, pars planitis [Figure 6][4]
- Following trauma, to identify angle recession and to assess the iris, ciliary body, angles, and the lens, especially in the presence of hyphema which obscures the view on slit lamp[4]
- To study the anatomy of anterior chamber, in the presence of dense corneal opacity, before surgical intervention [Figure 7][4]
- To identify anterior rotation of the ciliary body in uveal effusion syndrome [Figure 8][2]
- To assess the characteristics and the extension of anterior segment tumors [Figure 9][4]
- To study the extent of scleritis and to differentiate it from episcleritis[4]
- To study the position of the optic and the haptic of the intraocular lens.[4]
 | Figure 5: Ultrasound biomicroscopy of a case of phacomorphic glaucoma with angle closure
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 | Figure 6: Ultrasound biomicroscopy of a case with anterior uveitis showing pupillary block with iris bombe
Click here to view |
 | Figure 7: Ultrasound biomicroscopy showing a round, well-defined iris cyst behind the iris
Click here to view |
 | Figure 8: Ultrasound biomicroscopy of a case with uveal effusion syndrome showing anterior rotation of ciliary body with collection of fluid
Click here to view |
 | Figure 9: Ultrasound biomicroscopy showing a conjunctival mass extending over the cornea
Click here to view |
Limitations
- Inability to visualize structures deeper than 4 mm
- Requirement of immersion technique and an experienced operator to perform the scan
- Inability to perform UBM on eyes with an open corneal or scleral wound
- Requires contact, hence not useful in eyes with an open corneal or scleral wound, infections, and postoperative patients
- Need for the patient to lie in supine position while performing the scan
- Difficulty to perform UBM in children
- Possibility of causing injury to cornea with the eyecup, while performing UBM.
Even though newer techniques such as anterior segment optical coherence tomography and Pentacam have the added advantage of being noncontact with better resolution of anterior structures, UBM still stands superior because of the deeper penetration and better visualization of ciliary body, zonules, and lens. The future prospect of three-dimensional-UBM imaging system to generate volumetric images of ocular structures, which is currently being developed, looks promising.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
| References | | |
| 1. | Pavlin CJ, Harasiewicz K, Sherar MD, Foster FS. Clinical use of ultrasound biomicroscopy. Ophthalmology 1991;98:287-95.  |
| 2. | Ishikawa H, Schuman JS. Anterior segment imaging: Ultrasound biomicroscopy. Ophthalmol Clin North Am 2004;17:7-20. |
| 3. | Kapetansky FM. A new water bath for ultrasonic biomicroscopy. Ophthalmic Surg Lasers 1997;28:605-6. |
| 4. | Bhat DC. Ultrasound biomicroscopy: An overview. J Clin Ophthalmol Res 2014;2:115-23. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
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