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| COMMISSIONED ARTICLE |
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| Year : 2014 | Volume
: 2
| Issue : 2 | Page : 115-123 |
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Ultrasound biomicroscopy: An overview
Deepak C Bhatt
UBM Institute, Mumbai, Maharashtra, India
| Date of Submission | 31-Jul-2013 |
| Date of Acceptance | 10-Oct-2013 |
| Date of Web Publication | 11-Apr-2014 |
Correspondence Address:
Deepak C Bhatt
UBM Institute, A/1 Ganesh Baug, 214 Bhalchandra Road, Matunga, Mumbai- 400 019, Maharashtra
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/2320-3897.130549
Ultrasound biomicrosopy (UBM) is a technique used to visualize the anterior segment of the eye using high frequency ultrasound. It uses 35-50 MHz probe which has a resolution of 40 microns and a depth of penetration of 4 mm. UBM is used to study the status of desment's membrane in cases of corneal edema when slit-lamp examination cannot see the desment's clearly. In open angle glaucoma, UBM does not have any significant role. In closed angle glaucoma, UBM helps to rule out occludable versus nonoccludable angles. UBM plays a major role in diagnosis of plateau iris configuration and malignant glaucoma. UBM helps to visualize the tract and bleb in cases of failed trabeculectomy and also helps in ruling out episcleal scarring or tenon's cyst. UBM is the only modality which can easily diagnose pars plannits or cyclitic membranes noninvasively. In cases of unexplained hypotony, UBM helps to diagnose ciliary body atrophy or traction on the ciliary body. In cases of trauma, it helps to rule out angle recession or cyclodialysis cleft. UBM can assess the extent of damage to the zonules in cases of trauma and also sees the integrity of posterior capsule. This article is a short overview and an introduction to the use of UBM in the evaluation of anterior segment pathologies and usefulness in treatment management. Keywords: Angle evaluation, anterior segment evaluation, ultrasound biomicroscopy
How to cite this article:
Bhatt DC. Ultrasound biomicroscopy: An overview. J Clin Ophthalmol Res 2014;2:115-23 |
Ultrasound biomicroscopy (UBM) is a technique used to visualize the anterior segment with the help of high frequency ultrasound transducer. The transducer used for posterior segment evaluation (B-scan) has a frequency of 10 MHz. Ten MHz frequency probe has a depth of 4 cms and a resolution of 940 microns. Therefore, this frequency is ideally suited for the posterior segment as all the structures imaged in the posterior segment have a thickness of more than a millimeter. The anterior segment has a depth of 4-5 mm and the structures are close to each other so we require a higher frequency probe. UBM (anterior segment ultrasonography) is performed with a 35 and 50 MHz probe. The resolution of 50 MHz probe is 40 microns and the depth of penetration is 4 mm. The purpose of this article is to write the basics of UBM and provide some images of important conditions.
| History | |  |
Dr. Charles Pavlin and Prof. Stuart Foster developed UBM at the Princess Margeret Hospital at Toronto, Canada in 1989. They developed three probes-50, 80, and 100 MHz for clinical trials. [1] 80 and 100 MHz probes were used to see the cornea and the anterior chamber (AC), as the depth of penetration is only 2 mm. They reached to a conclusion that a 50 MHz is an ideal compromise between depth and resolution to visualize the entire anterior segment.
| Normal anatomy | | |
Images produced by UBM have a resolution of 40 microns; hence, they are seen similar to those seen on a low power microscope. [2]
The cornea is the first structure seen on UBM [Figure 1]. The corneal layers are well-differentiated. The Bowman's membrane is seen as a first dense echo. The stroma shows low irregular reflectivity. The desment's membrane is seen as a dense highly reflective line. The corneoscleral junction can be differentiated because of the lower internal reflectivity of the cornea compared to the sclera.
The AC is seen as an echo poor area between the cornea and the iris. The AC depth can be measured from the posterior surface of the cornea to the anterior capsule. The normal AC depth is 2.5-3.0 mm.
The iris is seen as a flat uniform echogenic area [Figure 2]. The iris and ciliary body converge in the iris recess and insert into the scleral spur. The area under the peripheral iris and above the ciliary processes is defined as the ciliary sulcus. In general, the iris profile is straight in contrast to anterior bowing in pupillary block glaucoma and posterior bowing in pigment dispersion glaucoma. | Figure 2: Angle evaluation: Down arrow shows the sclera spur and up arrow the iris
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The angle can be studied in a cross-section by orienting the probe in a radial fashion at the limbus. The scleral spur is the most important landmark in the angle on UBM. The scleral spur is seen as small echogenic dot when the line between the sclera and ciliary body is traced to the AC. The ciliary body can be clearly defined by UBM from the ciliary processes to the para plana [Figure 3]. The ciliary processes vary in appearances and configuration [Figure 4]. The axial view of the ciliary processes is seen when taking a section of the angle. The individual processes are better seen in a transverse section through the ciliary processes. The posterior ciliary body tapers off toward the para plana.  | Figure 3: Ciliary body region: Up arrow shows the ciliary processes and down arrow the ciliary body
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The anterior zonular surface can be consistently imaged by UBM [Figure 5]. The zonules are seen as a medium reflective line extending from the ciliary processes to the lens surface.
The peripheral retina and pars plana region can be visualized as far peripherally as the probe can be moved before eyecup prevents the movement of the transducer. The retina in this region is thin and generally is imaged as a single line that cannot be differentiated from the retinal pigment epithelium unless detached. The composite image of the anterior segment on UBM can be seen as a transverse section between one ora serrata to opposite ora serrata [Figure 6]. | Figure 6: Cross section of anterior segment from one ora to opposite ora serrata
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| Indications for UBM | | |
- Glaucoma: UBM helps to study the angle in great detail. The exact configuration of the iris, ciliary body, and processes can be defined. These structures can be seen in the presence of an opaque media. The angle can be quantified and the values can be followed up after treatment. [3]
- Uveitis: UBM is helpful in the study of anterior uveitis. The presence of pars planitis, supraciliary effusion, cyclitic membranes, and ciliary body detachments can be visualized on UBM.
- Trauma: Anterior segment trauma is usually associated with hyphema. In presence of hyphema, it is difficult to visualize the iris and lens. UBM is helpful to study the position of the lens, the status of the iris, ciliary body, and the configuration of the angle. Angle recession and cyclodialysis cleft can be evaluated on UBM.
- Opaque media: In presence of dense corneal opacity, UBM is helpful to study the anatomy of the anterior segment before surgical intervention.
- Tumors: UBM is helpful to quantify the characterize tumors in the anterior segment and to study the entire extend of the tumor.
- Scleritis: UBM helps to differentiate scleritis from episcleritis and also helps to differentiate the various types of scleritis. It is also helpful to study the extent of scleritis and to rule out the involvement of the ciliary body and choroid.
| Limitations | | |
The most important limitation of UBM is depth. UBM cannot visualize structures deeper than 4 mm from the surface. The other limitation of UBM is that it cannot be performed in presence of an open corneal or scleral wound.
Anterior scleritis
Inflammation over the sclera warrants two questions to be asked namely whether the inflammation is in the episclera or sclera and what is the type of scleritis? Slip-lamp may not always distinguish between benign nondestructive scleritis and sclera necrosis (especially in presence of severe scleritis). The underlying scleral thickness can be measured and scleral thinning can be ruled out.
Episcleritis typically shows thickening, low reflectivity, and homogenicity of the episcleral tissue. Below the episcleral margin the sclera is normal [Figure 7]. | Figure 7: Episcleritis: Down arrow shows enlargement of the episclera and up arrow shows the normal sclera
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Episcleral tissue has large amount of ground substance and loosely organized connective tissue. Inflammation can spread rapidly, leading to vessel dilatation, edema, and cellular infiltration. Therefore, the low reflectivity observed in the UBM picture in episcleritis is in agreement with the loose tissue composition seen histologically. [4] In diffuse scleritis, the sclera is diffusely thickened. The inflamed scleral tissue has lower reflectivity with hyporeflective areas [Figure 8]. In nodular scleritis, scleral thickening and hyporeflectivity typically are focal with distinct borders [Figure 9].  | Figure 8: Diffuse scleritis: Left arrow shows marked diffuse thickening of the sclera, up arrow shows marked thinning of the remaining sclera
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 | Figure 9: Nodular scleritis: In nodular scleritis, there is nodular appearance of the sclera with ill-defined margins
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The role of UBM is to monitor the progress of disease and alert the possibility of scleral necrosis. Early necrosis is seen as a low-reflective pockets or more diffuse changes to hyporeflectivity arising within the inflamed sclera. Patients with such hyporeflectivity should be monitored carefully for progression to necrosis. [5]
Occasionally, there may be choroidal thickening, ciliary body thickening, and ciliary membranes associated with scleritis [Figure 10]. These areas may not be visible with any other modality. | Figure 10: Ciliary membranes: Pars planitis or iridocyclitis may lead to formation of cyclitic membranes (up arrow)
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Tumors of the anterior surface of the eye
Tumors and tumor-like conditions over the sclera, conjunctiva, and cornea can be easily diagnosed by direct examination. The role of UBM in anterior surface tumors is to assess the depth of the tumor and study the layer of origin of the tumor. Such assessment by UBM helps in treatment planning of tumors. UBM helps to study the amount of infiltration of the cornea and sclera in limbal tumors. [Figure 11] shows a small corneal nodule. This nodule is well-visualized on slip-lamp, but the role of UBM is to study the base of the lesion. There is no infiltration of the Bowman's capsule by the nodule. [Figure 12] shows a nonresolving scleral nodule for more than a year. Patient had received multiple doses of steroid, but there was no resolution of the nodule. On UBM, the nodule shows a small echogenic area with shadowing suggestive of a small foreign body. The foreign body was removed and the nodule resolved. Hence, UBM is helpful in determining the cause of scleral nodules. [Figure 13] shows a diffuse conjunctival lesion. UBM shows that the lesion is superficial to the sclera and there is no thickening or infiltration of the sclera. [Figure 14] shows a large diffuse scleral nodule with infiltration of the cornea and sclera. | Figure 11: Corneal nodule: Down arrow shows a well-defined corneal nodule with intact bowman membrane
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 | Figure 13: Limbal nodule: Large limbal nodule noted with good plane between the nodule and sclera (down arrow)
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 | Figure 14: Limbal nodule: Large limbal nodule with infi ltration of the sclera and cornea (down arrow)
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Glaucoma
Glaucoma is a progressive optic neuropathy (a disease of the optic nerve) characterized by a specific pattern of optic nerve head and visual field damage.
Glaucoma is broadly classified as open angle and narrow angle glaucoma.
The role of UBM in open angle glaucoma is limited but in narrow angle glaucoma that UBM plays an important role.
Differential diagnosis of the angle-closure glaucomas
Although eyes with angle-closure glaucoma share differentiating features, the classification of this group of disorders is best made according to the anatomic findings that cause the iridotrabecular contact. Forces acting at four anatomic levels may alter the configuration of the AC angle and predispose to angle-closure glaucoma. These include the iris (pupillary block), the ciliary body (plateau iris), the lens (phacomorphic glaucoma), and forces posterior to the lens. This classification facilitates an understanding of the various mechanisms involved in the disease process and permits treatment to be directed at the underlying pathophysiology.
Pupillary block glaucoma
Pupillary block glaucoma is usually diagnosed on indentation gonioscopy.
On UBM, pupillary block glaucoma is seen as classical iris-bombe configuration. The angles are shallow to close. The AC is shallow. There is minimal iris-lens contact. The ciliary sulcus is open and there is no rotation of the ciliary body [Figure 15]. [6]  | Figure 15: Iris bombe: Dome-shaped elevation of the iris causing angle closure (up arrow)
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Plateau iris configuration
Plateau iris configuration results from a large or anteriorly positioned pars plicata that mechanically holds the ciliary body against the trabecular meshwork. The iris root is inserted anteriorly on the ciliary face so that the angle seems crowded and narrow. The AC is usually not shallow and the iris surface seems flat or slightly convex [Figure 16]. | Figure 16: Plateau iris confi guration: Medial rotation of the ciliary body causing peripheral iris elevation and secondary angle closure (up arrow)
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Pseudoplateau iris
In pseudo-plateau iris, the clinical appearance of the AC angle is similar to that seen in plateau iris syndrome. The difference between these conditions is determined by the underlying mechanism that results in the typical appearance of the peripheral iris. In pseudo-plateau iris the anterior displacement of the peripheral iris is not caused by an enlarged or anteriorly positioned ciliary body. Cysts of the iris and/or ciliary body neuroepithelium are most often responsible [Figure 17]. These conditions usually affect one quadrant. Since the pathology is posterior to the iris UBM is the best investigation for this condition. | Figure 17: Iris cyst: A well-defined iris cyst with thin walls and clear fluid in the cyst (up arrow)
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Lens-related angle-closure
Abnormalities in the size or position of the lens can alter the anatomic relationship of the anterior segment structures leading to angle-closure glaucoma. Thus, causing anterior push on the iris centrally leading to secondary angle closure [Figure 18]. These conditions are collectively termed phacomorphic glaucoma. | Figure 18: Phacomorphic glaucoma: Enlarged anteroposterior diameter causing central iris elevation and secondary angle closure (down arrow)
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The lens can be pushed anteriorly secondary to laxity of zonules as in Marfan's syndrome or due to trauma. [7]
Malignant glaucoma
Malignant glaucoma, also known as ciliary block glaucoma or aqueous misdirection glaucoma, is a secondary angle-closure glaucoma characterized by elevated intraocular pressure, shallow AC, patent iridectomy, and normal posterior segment anatomy by ophthalmoscopy and B-scan ultrasonography. This condition is a relatively rare but serious complication of intraocular surgery.
On UBM in malignant glaucoma, there is medial or anterior rotation of the ciliary body and processes. There is anterior rotation of iris-lens diaphragm with shallow AC with complete angle closure [Figure 19]. The closest differential diagnosis to this is complete angle closure glaucoma [Figure 20]. In complete angle closure glaucoma, there is total iris-cornea apposition, but the lens is in normal position with large posterior chamber. | Figure 19: Malignant glaucoma: Malignant glaucoma causing anterior rotation of the iris-lens diaphragm (up arrow)
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 | Figure 20: Synechial angle closure: Synechial angle closure causing anterior iris rotation (up arrow) and intraocular lens is in position (down arrow) with large posterior chamber
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Pigment dispersion syndrome
Pigment dispersion syndrome is caused due to liberation of pigments from the iris epithelium.
On UBM, there is a deep AC with posterior bowing of the iris. There is posterior insertion of the iris root with iris-lens, iris-zonular apposition.
UBM ascertains the areas of iris-lens contact and helps to guide the exact site for iridectomy [Figure 21]. | Figure 21: Pigment dispersion syndrome: Posterior bowing of the iris (down arrow) causing touch between iris and zonules, causing pigment dispersion
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Quantitative angle analysis
The angle can be measured quantitatively using special software [Figure 22]. The angle recess area measured helps to study the exact change in the angle narrowing before and after provocation test.
Postglaucoma surgery status
UBM helps to study the exact anatomy of the operative site following trabeculectomy [Figure 23]. The iridectomy, internal ostium, tract, and bleb are well-visualized by UBM. A tenon's cyst is seen as a cystic lesion in the area of the bleb with multiple echoes and blocked external ostium [Figure 24]. Episcleral scarring is noted as dense echoes within the sclera, with no bleb formation and blockage of the external ostium [Figure 25]. [8]  | Figure 23: Normal trabeculectomy: Normal trabeculectomy is seen on ultrasound biomicrosopy well as it shows the tract (up arrow) and iridectomy (down arrow)
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 | Figure 24: Tenon's cyst: An ill-defined cyst is noted in the region of the bleb with multiple internal echoes (down arrow)
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 | Figure 25: Episcleral scarring: Episcleral scarring is noted as multiple dense echoes in the region of the bleb (down arrow)
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Ciliary body and processes
Ciliary body and processes is the area in the eye, which is inaccessible by routine light-based instruments such as the slit lamp.
UBM can directly visualize both the ciliary body and the ciliary processes. Supraciliary effusion is seen as fluid in the supraciliary space with medial rotation of the ciliary body leading to partial angle closure [Figure 26]. [9] UBM is helpful in cases of chronic irido-cyclitis to determine the presence of cyclitic membranes and rule out traction of the ciliary body [Figure 27].  | Figure 26: Supraciliary effusion: Suparciliary effusion is noted at fluid in between the ciliary body and sclera (left arrow)
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 | Figure 27: Cyclitic membranes: Cyclitic membranes are seen as thin irregular membranes in the region of the ciliary body
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IOL position and complications
UBM helps to study the position of the optic and the haptic of the intraocular lens (IOL). [Figure 28] shows the haptic in the capsular bag. [Figure 29] shows haptic in contact with iris and ciliary processes. In patients having recurrent iridocyclitis after cataract surgery, it is important to study the position of the haptics. In majority of these cases, it is possible to show the contact between the haptic and the uveal tissue (iris, ciliary body, or processes). This contract could be the cause of recurrent iridocyclitis or UGH syndrome.  | Figure 28: Normal intraocular lens position: The intraocular lens optic (down arrow) and haptic (up arrow) are seen clearly on Ultrasound biomicrosopy
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 | Figure 29: Position of intraocular lens: In cases of subluxation of the intraocular lens, the haptic position can be noted on ultrasound biomicrosopy. Haptic is seen in contact with ciliary processes
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Cornea
Cornea is usually well-visualized with slit-lamp examination. Whenever there is corneal edema, the desment's membrane cannot be completely visualized and hence desment's detachment cannot be ruled out. [Figure 30] shows marked corneal edema and desment's detachment.  | Figure 30: Descemet's detachment: In cases of thickening of the cornea the desment's detachment can be noted as a thin membrane separate from corneal stroma
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Anterior segment trauma
UBM is performed in cases of anterior segment trauma to study the extent of the trauma. UBM cannot be done in presence of an open wound. Angle recession is seen as deep angle beyond the scleral spur and tear of the ciliary processes [Figure 31]. Cyclodialysis cleft on UBM is seen as communication between the supraciliary space and AC [Figure 32]. The exact extent of zonular dialysis or stretching can be determined by UBM [Figure 33].  | Figure 31: Angle recession: Angle recession can be noted as widening of the angle from sclera spur posteriorly (left arrow)
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 | Figure 32: Cyclodialysis cleft: Cleft is noted as a communication between the anterior chamber and supraclliary space (up arrow)
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 | Figure 33: Zonular stretching: Zonular stretching is noted at thin echogenic lines stretched between the lens and ciliary processes
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| Conclusion | | |
Anterior segment diseases are well visualized by direct examination techniques. UBM plays a role in specific conditions. In cases of scleritis, it helps in differentiation of scleritis from episcleritis and helps in early detection of scleral necrosis.
In anterior segment tumors and tumor-like conditions, UBM helps to study the depth of the lesion and to delineate the layer of origin of tumor. This further helps in treatment planning of the patients. In glaucoma, it plays a role in differentiating various types of angle closure glaucoma and postoperative evaluation. In trauma, it helps to determine the extent of trauma to different anterior segment structure. [10]
| References | | |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23], [Figure 24], [Figure 25], [Figure 26], [Figure 27], [Figure 28], [Figure 29], [Figure 30], [Figure 31], [Figure 32], [Figure 33]
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