ULTRASOUND BIOMICROSCOPY

SIVATEJA CHALLA

LAYOUT

• INTRODUCTION• PRINCIPLE• TECHNIQUE• NORMAL ANATOMICAL STRUCTURES• APPLICATIONS• UBM VS AS OCT• LIMITATIONS

INTRODUCTION

INTRODUCTION

• Ultrasound biomicroscopy (UBM) provides high-resolution imaging of ocular structures anterior to the pars plana region of the eye

• Developed by Pavlin, Sherar and Foster in Toronto in the late 1980s

• Provides exceptionally detailed two-dimensional gray-scale images of the various anterior segment structures and evaluates them both quantitatively and qualitatively

PRINCIPLE

PRINCIPLE

• It acts on a principle similar to that of the B-scan (10Mhz)• Frequency 50Mhz • More frequency, less penetration(5mm) and more

resolution• Limited depth of penetration is also associated with a

smaller angular field (4x4 mm)• addition to the tissues easily seen using conventional

methods (ie, slit lamp), such as the cornea, iris, and sclera, structures including the ciliary body and zonules, hidden from clinical observation, can be imaged and their morphology assessed

TECHNIQUE

TECHNIQUE

There are three main components of the UBM machine.1.Transducer

2. High-frequency signal processing.

3. Video monitor

Transducer 50 MHz

This radiofrequency travels the body tissue and isreflected back to the transducer. The reflectedradio frequency is processed by the signal processing unit.

Signal processing unit

The signal processing unit in UBM is specially designed to handle high frequency signals.

Subtle movements.

Special motion control device.

Mounted on a pulley with the piezoelectric crystal fixed on a large handle

Patient in supine position

Local anesthetic

Eye cup (plastic or silicone) which is used to create a small water bath

Methyl cellulose or normal saline can be used as coupling solution

The reflected signal is best detected when the transducer is oriented so that the ultrasound beam strikes the targeted surface perpendicularly

The crystal of the transducer is placed in saline approximately 2 mm from the eye surface.

(This distance of 2 mm prevents injury to the cornea and also helps as a fluid standoff.)

NORMAL OCULAR STRUCTURES

NORMAL OCULAR STRUCTURES

Epithelium

Bowmanns membrane

Stroma

Endothelium and DM

The Scleral Spur Can Be Identified In The Region Where The Radiopaque Shadow Of The Sclera Merges With The Relatively Radiolucent Shadow Of The Cornea And Is Often Visible As A Change In The Configuration When The Inner Border As The Sclera Merges Into The Cornea.

APPLICATIONS

QUALITATIVE STUDIES AND QUANTITATIVE STUDIES

Quantitative Ultrasound Biomicroscopy

• Quantitative studies includes Simple measurements methods such as a) Distance

b) Angle measurement

Biometry of the Anterior Segment

Corneal thickness Anterior chamber depth Posterior chamber depth IOL thickness Iris thickness Ciliary body thickness Scleral thickness .

Cannot determine lens thickness (cannot penetrate till post capsule of lens)

Measurement of AC angle

Qualitative Ultrasound Biomicroscopy

• Glaucoma• Cornea• Tumors• Trauma• sclera• Intraocular lenses• Ocular adnexa

GLAUCOMA

open-angle glaucoma• can be used to measure the anterior

chamber angle in degrees

• assess the configuration of the peripheral iris

• evaluate the iris insertion in relation to the trabecular meshwork

• see if there is an anterior insertion of the iris or an anteriorly displaced ciliary body

Narrow angles• UBM shows the extent of angle

closure

• depth of the anterior and posterior chambers

• identifies pathologic processes pushing the lens and iris forward.

determine the mechanism of elevated intraocular pressure (angle-closure versus open-angle) by showing the relationship between the peripheral iris and trabecular meshwork.

PUPIL BLOCK GLAUCOMA

(A) The angle shows appositional closure owing to anterior bowing of the iris. (B) The angle is open with a flattened iris after laser peripheral iridotomy.

PLATEAU IRISPlateau iris has been defined based on UBM by Kumaret al if all criteria fulfilled in at least 2 quadrants:

1.The ciliary process was anteriorly directed, supporting the peripheral iris so that it was parallel to the trabecular meshwork.

2. The iris root had a steep rise from its point of insertion, followed by a downward angulation from the corneoscleral wall.

3. Presence of a central flat iris plane.

4. An absent ciliary sulcus.

5. Irido-angle contact (above the level of the scleral spur) in the same quadrant.

Kumar, et al. Prevalence of plateau iris in primary angle closuresuspects, a UBM study. Ophthalmology 2008;115:430-34.

To Determine Occludability of the Angle

• perform dark room provocative testing with the UBM, to study the spontaneous occlusion of the angle under conditions of decreased illumination

• Helps to identify “at risk” population which can then be subjected to a laser iridotomy

• better than dark room gonioscopy because the latter is time consuming and standardization of slit-lamp illumination is difficult

Congenital glaucoma

Common features- • thin stretched out ciliary body, • abnormal tissue at the irido corneal angle• abnormal insertion of the ciliary body

PIGMENT DISPERSION SYNDROME

classical picture• widely opened angle and typical• posterior bowing of the peripheral iris

Peripheral anterior synechiae

• reveal the extent of irido corneal adhesions, even if the cornea is hazy or opaque

Malignant glaucoma

• Extremely shallow anterior chamber,• occluded angle,• forward rotation of the ciliary body• with or without fluid in the suprachoroidal

space.

Functional Status of a Filtering Surgery

• whether the sclerostomy aperture is patent or blocked internally,

• whether the peripheral iridectomy is patent

• whether the filtering bleb is flat, shallow or deep

CORNEA

Graft host junction Epithelial bullae in oedema Corneal dystrophy

Lamellar keratoplasty Stromal scarring Adherent leucoma

Granular dystrophy

TUMOURS

• Iris tumors, ciliary body tumors and anterior choroidal tumors can be imaged

• Borders of the tumor are usually detectable by the change in reflectivity from surrounding structures

CHOROIDAL TUMOUR Irido ciliary cystThe most common clinical presentation of an irido-ciliary cyst is a peripheral iris elevation - the typical UBM finding of a thin walled structure with no internal reflectivity is diagnostic.

TRAUMA

CYCLODIALYSIS

Angle recession is imaged as a tear into the face of the ciliary body. Ciliary body tissue is still imaged attached to the scleral spur.

Zonular rupture

Hemorrhagic cyst within the iris

SCLERA

EPISCLERITIS

INTRAOCULAR LENSES

• Can be helpful in ana lyzing intraocular lens position and determining the source of the problem if all does not go well

• Ante rior chamber depth after surgery can be measured with a high degree of accuracy.

• margins of the optic can be easily imaged and decentration analysed

• Haptic loca tion in relationship to surrounding structures can be determined and, in the case of posterior chamber lenses, one can usually determine if the haptic is in the capsular bag

iris isadherent to a membrane on the surface of the lens

Conjunctival and Adnexal Disease

UBM AS-OCT• contact technique • Non contact technique

• Coupling media used • Not used

• Sound energy used • Light energy used

• Scleral spur less distinct • More distinct

• Posterior lens capsule not seen • Seen

• patient supine, positioning theoretically causes the iris diaphragm to fall back deepens the AC and opens the angle.

• Patient sitting,so no alterations

• pressure on the eyecup used while scanning can influence angle configuration

• Nil

• Only 1 quadrant can be imaged at a time • 4 quadrants can be scanned at once.

UBM AS-OCT• there is no fixed reference point and the angle

region measured is located subjectively as nasal, temporal, superior, inferior, and so forth, not in exact degrees of an arc

• With AS-OCT, keeping the fixation angle (the angle between the instrument’s optical axis and the eye’s line of sight) at 0 degree, finding the exact location of the measured angle in degrees of an arc is possible.

• UBM procedureis more time consuming and requires a highly skilled operator to obtain high-quality precision images.

• No skills required

Limitations• risk for infection or corneal abrasion because of

the contact nature of the examination

• it is contraindicated in suspected open-globe injuries.

Limitations• AS-OCT are that it cannot obtain clear images

through opaque media and is obstructed by the eyelids, making imaging of the superior and inferior angles difficult

• also provides limited visualization of the ciliary body.

LIMITATIONS

• The most important limitation of UBM is depth.UBM cannot visualize structures deeper more that4 mm from the surface.

• The other limitation is that UBM cannot be performed in presence of an open corneal or scleral wound.

THANK YOU