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OCULAR ULTRASONOGRAPHY(A-SCAN AND B-SCAN)

Dr. S. Rasaily

RESIDENT

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INTRODUCTION

Ultrasound is defined as sound that is beyond the range ofhuman hearing

Ultrasonography uses high frequency sound waves to

produce echoes as they strike interfaces between acousticallydistinct structures

Non-invasive ,efficient & inexpensive diagnostic tool to detect

& differentiate various ocular & orbital pathologies

Demonstrates morphology, characterises tissues & providesdynamic information

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INTRODUCTION

Indispensible tool

- calculation of IOL power, tissue thickness measurements

- evaluation of posterior segment behind dense cataract &vitreous haemorrhage

- diagnosis of complex vitreoretinal conditions

- differentiation of intraocular & orbital masses

- location of intraocular FB

Based on Principle of pulse echo technique andtissue acoustic impedance mismatch.

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History

1956- Mundt and Hughes (1STuse of industrial ultrasound toexamine enucleated eye with intraocular tumor)

1957- Oksala of Finland(1stclinical use of A-scan). 1958- Baum and Greenwood developed the B-scan using the

immersion method(first two dimensional), but the imagewas quite poor.

Purnell and Sokallu described orbital B-Scan evaluation andclassification of orbital disease with its help.

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History 1960- Jansson( Sweden) used USG to measure distance

between structures in the eye. 1970- Coleman and associates 1stcommercially available

immersion B- scan. Later Bronsonintroduced a contact B-scan machine. Ossoinig( Australian Ophthalmologist) -standardized

echography.

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Physics

Ophthalmic Ultrasound = 8-10 MHz( 1 MHz= 1,000,000 cycles/sec) Short wavelength( < 0.2 mm) have smallpenetration(6cm at 7.5MHz) but excellent resolution of smallstructures

Propogated as longitudinal wave consisting of compressions &rarefraction of molecules as the wave passes through themedium, that can propagate within fluid & solid substances

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Reflectivity

-When sound travels from one medium to another mediumof different acoustic impedences, part of the sound isreflected from the interface between those media backinto the probe. This is known as an echo;

Acoustic impedence = sound velocity x density

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The returning echoes are affected by many factors

1. Absorption and refraction

2. Angle of sound incidence

3. Size,Shape and Smoothness of acoustic interfaces

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Angle of Incidence

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Acoustic interfaces

Echoes are created by acoustic interfacescreated at the junction of two media thathave different acoustic impedance

The size shape and smoothness of aninterface play roles in the character ofreturning echoes

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Gain

Represents relative units of the ultrasound intensity(dB)

Adjusting gain does not change the amount of energyemitted from the transducer , it changes only the intensityof the returning echo that is displayed on the screen.

The higher the gain level, the greater the ability of the

instrument to display weaker echoes ( e.g vitreousopacities)

Conversely as the gain is lowered , only the stronger echoeswill continue to be displayed ( e.g retina and sclera)

Many instruments incorporates time gain compensation toenhance weak echoes displayed from deeper tissue layer.

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Pulse echo system

Emits ultrasound wave detects and processes and displaysreturning echoes

The basis of pulse echo system is piezoelectric elementsmade up of ceramic crystals or quartz

Piezoelectric crystals-mechanical vibration-longitudinalultrasound wave pause of several microseconds-allowstransducer rim to receive and process returning echoes

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Probe

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Schematic Diagram of ultrasoundsystem

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A-Scan

One dimensional acoustic display Echoes are represented as vertical spikes from a baseline The distance between any two spike can be calculated by

the formula D= V (velocity) x T (Time) Spikes represents reflectivity, location & size of anatomic

structure The height of the spikes corresponds to the strength

(amplitude ) of the echo. Various types of A-scans :

1. A -scan for axial length measurement2. Vector A -scan that can occur simultaneously on B-scan

echogram3. Standardized A-scan

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Interpretation of normal A-scan

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B- mode (brightness modulation)

Two dimensional acoustic section

An echo is represented as a dot ratherthan a spike

Strength of the echo is shown by thebrightness of the dot

A section of tissue is examined by anoscillating transducer that emits asound beam that slices through thetissue

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Interpretation of normal B-scan

At high gain reveals 2 echographic areasseparated by an echo free area

Echographic area at beginning of scan-

reverberations at tip of probe If good resolution- posterior convex

structure of crystalline lens

Large echo free area vitreous cavity

Echogenic area after vitreous-

retina,choroid,sclera & orbital tissues Retina seen as a concave surface proximally

Optic nerve shadow triangular shadowwithin orbital fat

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Techniques

It is best to begin with maximum gainon B scan

Patient is kept in a reclined positionrather than sitting position

Patients head and instruments aresituated close together so that probeposition and screen may be viewedsimultaneously

Methylcellulose applied to the face ofthe B-scan probe as a couplingmedium

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Techniques

Probe is placed directly on the eye (i.econjunctiva or cornea) opposite to the areaexamined

Marker on the probe act as the orientationpoint

Topical anaesthetic drops are applied to the

eye before examination

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Contact Techniques

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Immersion Techniques

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Techniques used for evaluation

1. Transverse Scans Shows lateral extent of the lesion Sound beam oscillates back and forth across the opposite

fundus producing a circumferential slice

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Techniques used for evaluation

1. Transverse Scans Horizontal transverse: Evaluate superior and inferior fundus

and marker is oriented towards nose Vertical transverse: Evaluate the nasal and temporal fundus

and marker is oriented superiorly Oblique transverse: Evaluate the pathology not located at

major meridians(3,6,9,12 oclock) and marker is orientedsuperiorly

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Techniques used for evaluation

2. Longitudinal Scans Sound beam sweeps along the meridian opposite the probe

rather than across the meridian.

Shows AP extent rather than a lateral extent.

Echogram- Optic disc and posterior fundus displayed on thelower portion of the screen

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Techniques used for evaluation

2. Longitudinal Scan

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Techniques used for evaluation

3. Axial techniqueHorizontal: marker towards the nose( macular region just below the optic disc).

Vertical: marker oriented superiorly

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A systematic approach to

Echographic examination is

recommended

1. Screeningfor lesion detection.

2. Topographic examinationie, shape, border and locationof lesion.

3. Quantitative echography, ie reflectivity, sound,

attenuation & internal structure of lesion.

4. Kinetic echography, ie mobility, vascularity, consistency

of lesion.

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1. Basic screening examination

To detect lesions in the posterior segment.

Both B-scan and A-scan can be used.

B-Scan screening technique:

Transverse and longitudinal scans of four major

meridian and axial scan High settings to detect vitreous opacities and gross fundus lesions

low settings to detect relatively flat fundus lesions.

A-scan screening technique:

At tissue sensitivity decibel (24db) setting.

Performed in 8 meridians - limbus to fornix,

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B-Scan screening

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3.Quantitative echography

1. Reflectivity : is estimated according to size,configuration,thickness ,density.

Comparision of spike height on A scan and signal

brightness in B scan2 Internal structure : degree of variation inhistologic architecture within a masslike lesion

a.Regular- little or no variation in height and

length of spikes on A-scan whereas uniformappearance of echoes on B-scan

b.Irregular- marked differences in echoes

appearance

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3.Quantitative echography

Sound attenuation :

-Sound energy is absorbed, scattered orreflected by a given medium

-Evaluated on both B- and A-scan

-Progressive decrease in strength of echoes

either within or posterior to a lesion

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3.Kinetic echography

1. Assess the motion of orwithin a lesions

Aftermovement -non solidslesion like vitreous membraneor retinal detachment

Vascularity fastspontaneous motion ofechoes on screen

Convection-slowspontaneous motion ofechoes seen(cholesteroldebris )

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BRIEFLY ULTRASOUND FINDINGS OF DIFFERENT

VITREORETINAL DISEASES

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Vitreous Haemorrhage

Pattern depends upon density, location, extent &associated fibrous changes

A-scan:

In fresh, mild with dispersed RBC -a chain of low

amplitude spikes

More dense haemorrhage- high reflectivity

If blood organizes larger interface - even higher

reflectivity(60-100%)

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Vitreous Haemorrhage

B-scan:- Appears as small white echoes

With greater density of vitreous haemorrhage - greater opacitiesFresh, diffuse & unclotted haemorrhage - very little or no echoes- Vitreous haemorrhage may be confined- within PVD

Thick inferiorly and thin superiorly

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Asteroid Hyalosis

A-scan -

multiple spikes of medium to high reflectivity

B-scan - Appears bright point like echo sources

opacities exhibit distinct movement on

movement of the eye

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Posterior Vitreous Detachment

A-scan:Tall single spike but not as tall as in RD

Reflectivity is low(5-10%) if post. vitreous layer is thin & high(80-90%) if

thick or lined by RBC

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Posteiror Vitreous Detachment

B-scan:

Appears as an undulating membrane in front of the retinochoroidal layerMay remain attached to optic disc or separated completely from the post. pole

Height of A-scan spike & brightness of B-scan of PVD reduces as gain is

reduced

Kinetic echography typically shows a very fluid ,undulating after movement of

PVD-this characteristics differentiates PVD from retinal and choroidal

detachment

l d h

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A-scan : Single, steeply rising, extremely high(100%) & moderately

thick retinal spike when sound beam is perpendicular toretinal surface

Lower & wider spikes with 2 or more peaks - oblique beam

Long chain of low to medium high spikes -tangential beam

Distance between the retinal spikes and the ocular wallspikes in a given beam direction is equal to the degree ofelevation.

Presence of signals between retinal & scleral spike-

indicative of exudative or hemorrhagic RD

Retinal detachment

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B-scan:

- Appears as a bright, continuous, somewhat foldedmembrane

Attached to optic nerve & ora serrata

Recent RD- mobile retina & translucent subretinal space

i l i l d h

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Tractional retinal detachment

Common in vascular retinopathies

Caused by strong adhesion of vitreousmembrane, bands or the post. hyaloid

face to retina & subsequent traction

Adhesion could be focal causing a tent

like, or broad-causing table top traction

of retina

Detached retina- concave configuration

Retinal tear

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Retinal tear Large are visualized easily & smaller ones require

meticulous examination

If fresh vitreous haemorrhage due to the retinal tearobscures the fundus view-mostly located in upper half ofretina

A-scan:

appears as a highly reflective tissue separate from the other fundusspikes

B-scan:

breach of tissue

Giant retinal breaks with detachments appear as rolled out tissue with

clear breach of tissue

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Evaluation of choroid

Retinochoroidal layer:

A-scan- tall spike

B-scan- smooth concave configuration

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Choroidal detachment

A-scan:A thick steeply rising 100% high spike just behind theretinal spikeOn lowering the gain the spike is double peaked

If choroidal haemorrhage- low to medium spikes insubchoroidal spaceIf choroidal effusion- echofree space

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B-scan:

Smooth, dome-shaped, thick membranous structure notinserted to the optic nerve

localized or involve entire fundus- kissing choroidaldetachment

little or no after movement on

kinetic scanning

Nature of Suprachoroidal fluid

In serous detachment- echolucent

Haemorrhagic - echodense

Diff ti ti f PVD RD d

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Differentiation of PVD ,RD and

Choroidal detachment

technique PVD RD Choroidaldetachment

topographic Smooth, open

funnel with orwithout disc or

fundus insertion

Smooth or folded,

open or closedfunnel with disc

insertion

Smooth ,dome or

flat ,no discinsertion

quantitative Variable spike

height < 100%

Steeply rising 100%

high spike

Steeply rising ,

thick, double

peaked 100% highspike

Kinetic (after

movement)

Marked to

moderate

Moderate to none Mild to none

E d hth l iti

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Endophthalmitis

A-scan:

Multiple echospikes with low to medium reflectivity(10-60%)With organization & membrane formation reflectivity increases

Chain of low amplitude spikes

B-scan:

Opacities are seen

Membrane formation - in severe cases

Choroidal thickening,choroidal detachment, RD, retained IOFB -

possible associated findings

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Di l t d l

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Dislocated lens A-scan:

- 2 smooth and high reflective surfaces spikes in front of ocular spike

B-scan:

- round or oval globular structure in the post. Vitreous

- strands of vitreous may be attached to dislocated lens

Acoustic shadowing is seen, implying that the lens could be cataractousor calcified

I t l f ig b d

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Intraocular foreign body

A-scan:

Steeply rising spike with extremely high reflectivity(100%)Reflectivity remains same with lower gain

Can also detect radiolucent FB missed on x-ray

Small spherical FB-pellet-shows high echospike followed by a long chain of

echospikes of decreasing height

Large FB has ant. & post.echospike- thickness can be measured

B-scan:

Metallic FB produce very bright signals

Shadowing artifact on the adjacent orbit

Round metallic FB-reverberation artifact behind FB

B-scan showing the intravitreal foreign body

P t i gl b t

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Posterior globe rupture

Breach of sclera & choroidal tissue with associated choroidal thickening

Associated findings:

-Vitreous haemorrhage

-Retained intraocular or intraorbital FB

-RD

O ti l i

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Optic nerve avulsion

Seen secondary to trauma and is rare

Vitreous hemorrhage may be present & actual peripapillary scleral break maybe seen; in long standing cases- proliferative tissue at optic disc

Optic disc dr sen

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Optic disc drusen

Calcified nodules seen echographically with high reflectivity at or within the

optic nerve head

Best seen with - transverse or longitudinal B-scan approach which bypasses

the lens

Evaluation of intraocular tumors

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Evaluation of intraocular tumors

Display different acoustic characteristic on USG due

to vast difference in histologic composition

B- scan: topographic features as shape, location, &extension

A- scan: structure, reflectivity, vascularity,& height

Serial USG: measures height & growth of tumor overa period of time

choroidal melanoma

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choroidal melanoma

Collar-button shaped choroidal melanoma indicating that tumor hasbroken through bruchsmembrane. A-scan pattern typical of melanoma,

with the high retinal spike on the surface of the lesion but low-to-mediuminternal reflectivity within the lesion. The sclera and orbital tissues are seenas spikes to the right of the lesion.No after movement of spikes- solid consistencyLow reflective spikes behind the sclera.

Choroidal hemangioma

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Choroidal hemangioma

Choroidal hemangioma with an associated exudative retinal

detachment. This lesion is composed of tightly compacted blood

vessels and, therefore, demonstrates high, regular internal reflectivity

on both B-scan and diagnostic A-scan.

Metastatic choroidal lesion

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Metastatic choroidal lesion

Metastatic choroidal lesion from the breast. The lesion has rather irregularborders, with medium-high, irregular internal reflectivity on both B-scan anddiagnostic A-scan(high internal reflectivity-60 to 80%)

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D/D of ocular melanoma

lesion location shape reflectivity structure vascularity

melanoma Choroidal/

Cil. body

Collar

button

Low-

medium

regular +

Metastatic

carcinoma

Post.

choroid

Diffuse/

irregular

Medium-

high

irregular _

Choroidal

hemangioma

Post.

choroid

dome high regular _

Choroidal

nevus

choroid dome high regular _

Choroidal

hemorrhage

choroid dome variable variable _

Retinoblastoma

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Retinoblastoma A-scan:

Irregular acoustic structure with high internalreflectivity(70-100%)

Spontaneous movement of lesion spikes

evidence of vascularity Axial length measured - normal or decreased

Depends upon size, degree of tumors, calcification

& necrosis

Retinoblastoma

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Retinoblastoma

B-scan:

If large- irregular echogenic mass involving vitreous, retina,

subretinal space

Area of calcification - high echogenicity- strong sound

attenuation-

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Choroidal Osteoma Very echo dense lesion

irregular surface contour shadowing of scleral and

orbital echoes

A scan- very highly

reflective broad spike fromthe lesion with markdecrease in height oforbital spike

Pthisis bulbi

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Pthisis bulbi

Globe is atrophic and shrunken, intraocular contents

are disorganized & intraocular calcification may bepresent

A-scan: Irregular pattern of high & low reflective

echospikes fill the globe

High reflective echospikes may be due to ossification Short axial length

B-scan: Multiple echogenic vit. opacities choroidal thickening calcification of ocular coats Absence of orbital echospikes

Posterior staphyloma

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Posterior staphyloma

Shallow excavation of the posterior pole with

smooth edge in high myopia

Lateral rectus muscle

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Lateral rectus muscle

Posterior scleritis

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Posteriorscleritis

Nodular posterior scleritis with fluid in the Tenon capsule. Thescan on the right demonstrates a positive T-sign at the insertionof the optic nerve

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Thyroid-related orbitopathy

Enlargement of the extraocular muscle belly. The tendinous insertion

of the extraocular muscle at the globe is not thickened, which is

characteristic of thyroid-related orbitopathy.

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Multiple signals (Reverberations)

Occur between the probe tip and a highly reflective surfaceor between two highly reflective ocular interfaces

May cause error in axial length measurements

Can be distinguished from true echoes by their position inthe echograms as well as by their more pronouncemovements

Calcified lens, intraocular implants, foreign

bodies, scleral buckles , air bubbles common producers

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f f

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Refraction Artefacts

The high lenticular propogation velocity canproduce apparent abnormalities of the posterior

pole that resembles tumor formation or

thickening of the choroid( Baums Bumps)

b / h d ff

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Absorption/ Shadowing effect

Blockage of sound wave transmission by a highly reflectiveinterface. This appears as a hypointense area behind abright echo.eg calcium, glass, bone, air, metal.

fl k

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Low reflective spikes

Seen in front of the retinal spike when performedat high gain

This is because the lateral portion of the ultrasoundbeam reaches the concave retina earlier than thecentral portion

ffi i fl id li

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Insufficient fluid coupling

Entrapment of air

between probe and the

eye

Display bright echoes

that represents multiple

signals between probeand entrapped air.

T

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Tumors

To detect the acoustic structure its thickness

should at least be 2mm Tumors located at the orbital apex are difficult to

recognize because of the attenuation of the soundand confluence of Optic Nerve and Muscles that

are inseparable ultrasonically.

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I l f i b di

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Intra ocular foreign bodies

If IOFBs surface is less than 1mm2ORif it isembedded in the sclera

Wooden FB initially be highly reflective butits decrease reflectivity makes difficult tolocalise

Small air bubbles may mimic IOFB but usuallydisappear within a day or two.

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If the sound beam is misaligned at an angle through the lens

and is not in the visual axis ,the posterior and or the anterior

lens spike is not of high amplitude

The posterior lens spike may be slightly shorter than anterior

lens spike because of its greater curvature however, if the

posterior lens spike is more than 10 percent shorter than the

anterior onemeans the sound beam is misaligned.

Corneal compression in the contact technique yields shorter

axial length.

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Ult d bi i

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Ultrasound biomicroscopy

Uses To evaluate ant. segment anatomy in eyes with corneal scars

before penetrating keratoplasty

To delineate the extent of iris & ciliary body tumors

To understand the pathology - mechanism of various types of

glaucoma

To locate ant. segment FB Measures anterior chamber depth.

Measures corneal thickness

C l D l Ult g h

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Color-Doppler Ultrasonography

Use of B-scan with color Doppler

Non-invasive approach to measure and visualize blood flow

in orbital vessels and tumors.

To evaluate many ocular disorders including glaucoma,

hypertension & ocular ischemia

Colour Doppler imaging of the

ophthalmic artery

RECENT ADVANCES

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RECENT ADVANCES

Recently used Power Doppler (PD) has three times the

sensitivity of conventional Color Doppler in detecting blood

flow & very useful in imaging of vascular lesions of the globe

and orbit

Recently, Silverman and colleagues developed a high-

frequency annular array transducer with higher depth of field

Other promising new developments in the field of diagnostic

ultrasound include tissue characterization and Echo contrast

agents (gas microbubbles)

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Three-dimensional (3D) ultrasound- 3-D image is constructed from a

series of ordered B-scan planes that are processed by special

software

Other promising developments in ultrasound in general include

refinement in transducer's material and technology, leading to

improvements in sensitivity and bandwidth

Reference

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References

1.Ultrasound of eye and orbit- Sandra Frazier Byrne

Ronald L. Green

2.Ultrasonography of the eye and orbitD. Jackson coleman

3.American Academy of Ophthalmology- Optics- 2013-2014

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Thank You