ultrasonographty in ophthalmology

7/29/2019 Ultrasonographty in ophthalmology

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ULTRASONOGRAPHY INOPHTHALMOLOGY

B-SCAN

UBM


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INTRODUCTION

One of the commonest non invasiveimaging investigative procedures

Complementary to CT & MRI

Cheaper, can be done in office setting

Done by Ophthalmologist with a dedicatedophthalmic US

All types of USG useful Wide range of applications

Particularly helpful in opaque media


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HISTORY

Mundt & Hughes (1956): A scan to evaluateintraocular tumour Oksala et al: A scan for diagnosis of intraocular

disorders / Data of sound velocities of variouscomponents of the eye

Baum & Greenwood (1958): B scan for Ophthalmicuse Jansson et al(1960): Used US to measure the

distances between different structures of the eye Coleman et al(1970): 1st commercially available

immersion B Scan Bronson: Contact B scan for Ophthalmic use Ossoinig (1960): Standardization of instrumentation

& technique Standardized Echography /Meticulous examination techniques


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ULTRASOUND

Acoustic wave of frequencies >20kHz

Diagnostic US in Ophth : 8-10 MHz

Higher frequency Better resolution Lower frequency Deeper penetration

Velocity depends on the medium

Longitudinal waves behave like light Refraction & Reflection property makes US

useful for diagnostic purpose


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B - SCAN

Brightness mode 2 Dimensional acoustic section where

echoes are plotted as dots Brightness of dots Strength of received

echo Uses focused beam from an oscillating

transducer that slices through tissue Useful in evaluation of intraocular structures

with opaque media & of orbital lesions Biggest advantage: Dynamic Echography


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Rapidly repeating short bursts ofultrasonic energy are beamed intoocular & orbital tissue.

Multiple short pulses of ultrasoundenergy are produced with a briefinterval between the pulses that

allows for the returning echoes to bedetected, processed & displayed.

Pulse-Echo Technque:


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ECHOES

Echoes are produced by interfaces

created at junction of 2 media ofdifferent acoustic impedances

Ac. Impedance = Velocity x Density

Greater difference in Impedance Stronger reflection (Echo)


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Medium 1 Medium 2

Medium 1 Medium 3

ACOUSTIC IMPENDANCE


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Returning of Echoes

Angle of sound incidence

Size, shape & smoothness of acousticinterfaces

Absorption

Scattering Refraction


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Different Types of Acoustic Interfaces


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Schematic Diagram of Ultrasound System

Transducer


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Probe / Transducer

(10 MHz) The part of US system where the US is

produced & through which the echoes arereceived

When stimulated by electric energy,Piezoelectric crystal located near the face ofthe probe undergoes mechanical vibrationproducing US in pulses.

The vibration of the echo produces anelectric signal that is transmitted to thereceiver, which is then processed.


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B-Scan Transducer


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Signal Processing

Electric Signal produced by returningecho is initially received as a very

weak RF signal which undergoes acomplex processing comprising of :

# Amplification

# Compensation

# Compression

# Demodulation

# Rejection


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DISPLAY MODES:

The processed signal is desplayed oncathode ray tubes in one two modes-

Ascan or Bscan.


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Concept of B-scan

interpretation: Real time- images can be visualised at

approx.32/sec,allowing motion of

globe & vitrious. Gray scale-returning echoes are two

dimensional images.

strong echoes-brightWeak echoes- lighter shades of gray.


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B - SCAN


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B-Scan Exam Techniques

for the Globe

Transverse

Longitudinal

Axial

Ant Segment : Contact

Post Segment : Immersion

SCANS:


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Transverse Scans


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Longitudinal Scans


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Axial Scans

Probe face centered on the cornea withpatient in primary gaze

Sound attenuation & refraction from thelens hinder resolution of the posteriorsegment

Helpful for lesions in relation to the lens &

optic nerve Can be useful for evaluation of macular

region


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Basic B-Scan Screening

Examinations

Transverse scans of 4 major quadrants

Longitudinal scans along 4 majormeridians

Vertical & Horizontal axial scans

Procedures performed both at high &low gain settings


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Special Exam Techniques

TopographicLocation

Extension

Shape

QuantitativeReflectivity

Internal structure

Sound attenuation Kinetic

Mobility : Aftermovement

Vascularity : Blood Flow


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Topographic Evaluation

Transverse scan Lateral extent

Longitudinal scan Radial extent

Axial scan Relationship of the lesionto anatomical landmark of lens & optic

nerve


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Quantitative Echography

Reflectivity : signal brightnessInternal Structure : echodensity

Sound Attenuation : Progressivedecrease in the strength of echoes,either within or posterior to a lesion


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Kinetic Echography

Used to dynamically assess the motionof or within a lesion

Aftermovement : motion of the lesionechoes following cessation of eyemovement

Vascularity : Spontaneous motion ofechoes


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Evaluation of Vitreous

Normal vitreous : In young, no echo.

In old, scattered echoes of lowreflectivity for opacities & fine thin linefor PVD

Asteroid Hyalosis : Diffuse or focalbright, point like echoes


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Asteroid Hyalosis


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Vitreous Haemorrhage

Fresh & mild : Dots & short lines

Dense : Greater no. of bright dots Organization : Larger interfaces


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PVD

Thin undulating irregular membrane ofirregular echotexture

Kinetic echography: Distinct AftermovementEven in presence of attachment to optic disc

May be focal or extensive

May separate completely from post. pole or

may remain attach to optic disc Challenging to differentiate from RD & CD


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PVD attached to Disc


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PVD with VH


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Endophthalmitis

Very useful for determining the severity &extent of the infection

Irregular low intensity echoes seen as

diffuse fine dots on B-Scan Appreciated only on high gains in early

stage Differentiation from VH :

- Heterogenous (VH : Homogenous)- PVD more extensive in VH- Pseudomembrane more common in VH


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Endophthalmitis


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Retinal Evaluation

Retinal Tears : High reflectivity with slightaftermovement

RD: Bright, Continuous Membrane of

uniform echotexture

: Mobility depends on type of RD &associated findings

: Besides topography, B-Scan is useful indetermination of configuration

: Hole, tear, band should be looked for


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Rheg RD

Membrane of uniform echotexture(even at low gain)

Minimum aftermovement

Flickering movement over themembrane : Diagnostic


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Rheg RD


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Exd RD

Usually Shallow RD

Marked thickening of Chorio-Retinal

Layer Marked Mobility


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Exd RD


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RD vs. PVD

RD PVD

Echotexture Thick, Uniform Thin,Undulating

Aftermovement No or Minimum Free Movement

Attachment toOptic Disc

Smooth Irregular

Reflectivity @low gain

Homogenous Irregular orAbsent

Peripheral

Reflectivity

100% Reduced


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PDR

Demonstrates the nature & extent

Useful in monitoring progression

Helps pre-vitrectomy evaluations

* Timing of surgery

* Planning of Surgery

* Optimal placement of instruments

* Visual prognosis


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PDR

Fibrovascular Membrane

Subhyaloid Hemorrhage

Vitreous Hemorrhage

PVD

TRD

Combined Rheg RD with TRD


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Retinoschisis

B-Scan : Smooth, thin, dome shapedmembrane not inserting to optic disc

Typically located inferotemporally

Differs from RD by its more focal,

smooth & thin character


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Choroidal Evaluation

Choroidal Thickening :

* Edema Highly reflective

* Diffuse inflammatory infiltrationLow to medium reflective

Mildly elevated, diffuse choroidal

tumors can be confused withnonspecific choroidal thickening


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Choroidal Detachment

B-Scan : Smooth, thick, dome shapedmembrane at periphery with little

aftermovement


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Choroidal Detachment


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Evaluation of Sclera

Posterior Scleritis :* Best imaging modality

* Thickened hyperechoeic sclera

* Hypoechoic rim around sclera* T sign : Diagnostic

Staphyloma :Diffuse thinning Coloboma of ON :Defect in post. sclera

Scleral Rupture :Break in sclera, Vitreous Thickened chorioretinal layer incarceration, Hge in Tenons space,


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Intraocular Tumors

The most important noninvasive adjunct toclinical exam even in presence of clearmedia

Standard Echography is valuable inevaluation of intraocular tumors

Provides accurate measurements, thereforevaluable for assessment of tumor growth orregression

Helpful in detecting extrascleral extension


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Detection of Tumors

At least 0.8mm elevation forultrasonographic detection

2-3mm height required for effectivequantitative evaluation

Solid Tumors :

No aftermovement of surface

Presence of internal echoes


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Choroidal Melanoma

B-Scan

Dome or Collarbutton shaped

Uniform iso orhypoechoic texture

Highly vascular :

Fast flickeringmovement


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Choroidal Melanoma


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Retinoblastoma

Irregular dome shaped mass lesionwith broad base over the retina

Calcification when present : Diagnostic Mixed Echotexture

Normal Axial Length

High Irregular Reflectivity

Distal Shadowing


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USG in Traumatized Globe

Great value, specially in trauma by missiledFB

Lid swelling : Exam through closed lids Any open wound should be repaired prior to

examination

Very high gain settings when examined

through closed lids Knowledge of various post traumatic ocular

changes is necessary


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IOFB

Dense short linear echo

Distal shadowing

Spherical FB : Dense echogenic distalshadow

Freely floating FB : No distal shadow

May get masked by associated VH


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Freely Floating IOFB


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USG in Post Op.

Dropped Nucleus / Lens / IOL

Scleral Buckle

Intraocular Gas

Silicon Oil

Suprachoroidal Hemorrhage


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USG Orbit

Orbital Soft Tissue Assessment

Extraocular Muscle Evaluation

Retrobulbar Optic Nerve

Examination


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Orbital MassDifferentiation

Topographic : Location, Shape,

Borders, Contour abnormalities Quantitative : Internal reflectivity,

Internal structure, Sound attenuation

Kinetic : Consistency, Vascularity,Mobility


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Evaluation of EOM

Effective in subtle & early muscle sizechange

Useful to differentiate various causesof muscle enlargement

Less echo-dense than orbital soft

tissue on B-Scan


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Evaluation of Rectii

Medial Rectus : Primary gaze, Probeon temporal equator

Lateral Rectus : 10Temporally,Probe placed medially

Inferior Rectus : 10Inferiorly, Probeplaced superiorly on the upper lid

SR & LPS : Primary gaze / Slightlysuperiorly, Probe inferiorly


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Evaluation of Obliques

SO Tendon : Horizontal transverse scanthrough the superior orbit

SO Belly : Oblique transverse scan throughthe superonasal orbit

IO Tendon : Oblique transverse scanthrough inferotemporal orbit

IO Belly : Difficult to display. Whenthickened : Horizontal transverse scanthrough most ant. aspect of inf. orbit


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Optic N Evaluation

B-Scan can evaluate topography &relationship of ON

Usually performed in medium gainAxial, Longitudinal & Transverse scan


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Optic Disc Evaluation

B-Scan can demonstrate excavation,elevation & drusen of Optic Disc

Axial, Longitudinal & VerticalTransverse approaches are useful

A-Scan useful in assessing reflectivity

& height of certain lesions of OD

UBM


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UBM High frequency US : 35-100 MHz

Provides near microscopictwodimensional gray scale images of

anterior segment Extensive use in Glaucoma

Also useful in ant. segment disorders

including cysts & tumors with cloudy /opaque cornea, blunt trauma,canalicular imaging etc.

P i i l


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Principle:

There are wide range of frequenciesranging from10- 20000Hzto>10/12Hz.

Resolution is related to full widthof US beam at half max amplitude(FWHM)=cf/vd=wavelengthC-speed of sound.

F- focal length of transducer.V-frequency.D-diam of transducer.Incresed resolution is accompanied by

loss of penetration.

D i f UBM


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Design of UBM

Scanner detected signals aredigitalised.

Transducermade up of pizoelectricpolymer PVDF & copolymer PVDF.Itachieves highest resolution & good

depth of focus.

I t t ti


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Instrumentation:

Front panel consists of large highresolution LCD screen.

Rear panel which plugs for connectionto probe,monitor & power connector.

HF Probe which are light weight accept35-50 MHz transducer & scan at 38 or20 degree scan angles at 15 mm maxscan depth.

Immersion cup

35 MHz transducer offer 70 of axial

resolution & 50 MHz offer 50.


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Examnation Technique:

Patients:supine with eye fixated at ceiling. Topical anaesthesia-immersion cup is placed

with lips of cup under the lids.

Fluid coupling medium instilled. Transducer have no membrane cover&

moves at the rate of 8passes/sec.It isplaced opposite the area of intrest.

Pt. is asked to look away from site ofpathology to bring pathological area into ex.Position.


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Probe orientation

Transverse Scan

Longitudinal scan

Axial Scan.

M t f l


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Measurment of ocularstrucure:

Depends on speed of a sound instructure.

It consists of time required for soundto traverse the tissue & return totransducer.

Mainly 1550m/sec speed of sound isused which increases accuracy tomeasure AC depth,iris thickness,C.B.


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Mesurment modes:

Vector 1550-linear measurement

Callipers-pairs of linear cursor for

linear measurment.Angle Measure

Biometry -accurate dist. Measurement

in ant .seg. Along optical axis.


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Normal ocular structure:

Cornea: layers appreciated

epi.-smooth surface line.

Stroma-reveals internalreflectivity.

B.M.s-highly reflective line.

AC-Its easy if internal corneal surface&ant surface of lens is clearlyapreceatd.


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Angle region: probe is oriented in radialfashion above the limbus.

Scleral spur is reffering pt. for measuringangle.

TrabecularIris angle:bet. Apex of irisrecess & arms passing through the

meshwork 500 m from scleral spur & thept. of iris perpendicularly ,opposite ismeasured.N-30 +/- .


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ZONULES & LENS:Ant zonules Iris:Thickness& curvature of iris is measured

highly reflective layer on post. Surface helpsin differnciating intra-iris lesion from thelesion behind iris.

Cilliary body: shows configurations of cilliaryprocesses & vallies bet. them

dist. Bet. Ant. Trabecular meshwork & cilliaryprocesses is measured & ant lens surface canbe seen.


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Quantitative Measurments:

AOD: bet. TM & IRIS at 500m ant toscleral spur.

TIA:ang of iris recess. ID1:iris thickness at 500m ant to s. spur.

ID2: iris thickness at 2 mm from iris route

ID3: Max iris thickness near pupillary edge

TCPD;bet TM& C.P. at 500m ant to s.spur.

ICPD; bet iris & CP. Along the line of TCPD.


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IZD:Bet iris & zonules Along the line ofTCPD.

ILCD: Contact dist. Bet iris & lens Iris lens ang: ang . Near pupillary

edge.


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CLINICAL USES:

Cornea: conj. Mass lesion

pre PK evaluation of ant seg

corneal thickness


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Glaucoma: evaluate post op shallow AC

malignant glaucoma

plateau iris

PDSiridozonular contact

bleb evaluation

cyclodylasis cleft


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Lens: zonular inttegrityPC integrityHaptic position

Uvea:Parsplanitis in media opacityscleritis

Vitrioretinal diseases:sclerotomy sitepars plana FB

Peripheral VR disMas lesions: iris & CB cyst, umors& lid lesions


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The sclera is imaged as a highlyreflective structure compared to thecornea. One can generally differentiatethe sclera from overlying episclera and

underlying ciliary body and retina


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Scleral thinning can be imaged and thethickness of residual sclera quantified


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Scleritis shows relatively low reflectiveregions within the sclera likely representingedema and inflammatory infiltrates.


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The anterior zonule can normally be clearlyimaged. Disruption will result in absentzonules, increased lens sphericity, andincreased distance of the lens margin from

the ciliary body.


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Cyclodialysis shows completedisinsertion of the ciliary body fromthe scleral spur accompanied by a 360

degree supraciliary effusion


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Anterior segment foreign bodies can belocalized. They generally present as areflective lesion with shadowing of

structures behind the foreign body.

IRIDOCILLIARY
http://www.nyee.edu/images/ubm9.jpg


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IRIDOCILLIARYCYST

Ciliary Body or

Iris Tumor

Accommodation and Iris
http://www.nyee.edu/images/ubm10.jpghttp://www.nyee.edu/images/ubm9.jpg


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Accommodation and IrisConfiguration
http://www.nyee.edu/images/ubm15.jpg


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ultrasonographty in ophthalmology

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