Ultrasonography: Principle, Methods & Detection of various Ocular Disease

1. ULTRASONOGRAPHY:
Principle, Method & Detection of
Various Ocular Disease
Sarmila Acharya
B. Optometry
18th Batch

2. Presentation layout
 Introduction
 History
 Physics
 Principles & instrumentation
 Terminologies
 Indications & contraindications
 Methods
- A-Scan
- B-Scan
 Interpretation

3. Introduction
 Sound has been used clinically as an alternative to light in
the diagnostic evaluation of variety of conditions
 Advantage of sound over light is it can pass through
opaque tissue
 An important tool in terms of diagnosis and management
 Is a non-invasive investigation of choice to study eye in
opaque media

4. Definition
Ultrasound Waves are acoustic waves that have
frequencies greater than 20 KHz
The human ear can respond to an audible frequency
range, roughly 20 Hz - 20 kHz

5. History
• In 1956
• First time: Mundt and Hughes, American Oph.
• A-scan (Time Amplitude ) to demonstrate various ocular
disease
• Oksala et al in Finland
• Ultrasound Basic Principle (Pulse-Echo Technique)
• Studied reflective properties of globe
• In 1958, Baum and Greenwood
• Developed the first two-dimensional(immersion) (B-scan)
ultrasound instrument for ophthalmology
• In the early 1960s, Jansson and associates, in Sweden,
• Used ultrasound to measure the distances between
structures in the eye

6.  In the 1960s, Ossoinig, an Austrian ophthalmologist
First emphasized the importance of standardizing
instrumentation and technique
Developed standardized A-scan
 In 1972, Coleman and associates made
First commercially available immersion B -scan
instrument
Refined techniques for measuring axial length, AC
depth, lens thickness
 Bronson in 1974 made contact B scan machine

7. Advantages of USG
 Easy to use
 No ionizing radiation
 Excellent tissue differentiation
 Cost effectiveness

8. Primary Uses In Ophthalmology
Posterior segment evaluation in hazy media / orbit
Structural integrity of eye but no functional integrity
Detection and differentiation of intraocular and orbital
lesions
Tissue thickness measurements
Location of intra ocular foreign body
Ocular biometry for IOL power calculations

9. Physics
 Ultrasound is an acoustic wave that consists of an
oscillation of particles that vibrate in the direction of the
propagation
 Longitudinal waves
Consist of alternate compression and rarefaction of
molecules of the media
Oscillation of particles is characterized by velocity,
frequency & wavelength

10. VELOCITY
Velocity=wavelength*frequency
v=λ * μ
Depends on the density of the media
Takes 33 micro sec to come back from posterior pole
to transducer
About 1500 m/sec average velocity in phakic eye and
1532 m/sec in aphakic eye

11. Sound wave velocities through various media
Medium Velocity (m/sec)
Water 1,480
Aqueous/ Vitreous 1,532
Silicon Lens 1,486
Crystalline Lens 1,641
PMMA Lens 2,718
Silicon Oil 986
Tissue 1,550
Bone 3,500

12. Frequency
Ophthalmic ultrasonography uses frequency ranging
from 6 to 20 MHz
High frequency provide better resolution
8 MHz in A scan
10 MHz in B scan
Low frequency (1-2 MHz)used in body scanning gives
better penetration

13. Wavelength
Wavelength is approx. 0.2mm
Good resolution of minute ocular & orbital structures
f α1/λ α resolution α 1/penetration
FREQUENCY VS
PENETRATION

14. Reflectivity
 When sound travels from one medium to another medium of
different density, part of the sound is back into the probe
 This is known as an echo; the greater the density difference
at that interface
- the stronger the echo, or
- the higher the reflectivity

15. In A-scan USG echoes are represented as spikes arising from
a baseline
The stronger the echo, the higher the spike
In B-scan USG echoes of which are represented as a
multitude of dots that together form an image on the screen
The stronger the echo, the brighter the dot

16. Absorption
Ultrasound is absorbed by every medium through which it
passes
The more dense the medium, the greater the amount of
absorption
The density of the solid lid structure results in absorption
of part of the sound wave when B-scan is performed
through the closed eye thereby compromising the image
of the posterior segment

17. B-scan should be performed on the open eye unless
the patient is a small child or has an open wound
When performing an USG through a dense cataract,
- more of the sound is absorbed by the dense cataractous
lens
- less is able to pass through to the next medium
- resulting in weaker echoes and images on both A-scan
and B-scan
The best images of the posterior segment are obtained when
the probe is in contact with the sclera rather than the corneal
surface, bypassing the crystalline lens or IOL implant

18. ECHOLOCATION

19. Ultrasound Echo
 Ultrasound wave
Refraction & reflection
 Echo (reflected portion of wave)
Produced by acoustic interfaces
Created at the junction of two media that have
different acoustic impedances
Determined by sound velocity & density
Acoustic impedance = sound velocity × density

20. Factors influencing the returning echo
( Height in A-Scan & Brightness in B-Scan )
1. Angle of the sound beam
2. Interface
3. Size and shape of interfaces

21.  Angle at which a sound beam encounters an ocular structure
 Sound beam directed perpendicularly to a structure
maximum amount of sound will be reflected back to
the probe
 The farther away from the ideal angle
the lower the amplitude
a) Angle of Incidence

22. Relative difference between various tissues that the
sound beam encounters
Strong or weak echoes due to the significance of tissue
interface
 For example:
- The difference in interface between vitreous and fresh
blood is very slight resulting in small echo
- The difference between a detached retina and the
vitreous is great producing a large echo
b) Interface

23. Smooth surface like retina will give strong
reflection
Smooth and rounded surface scatters the
beam
Coarse surface like ciliary body or
membrane with folds tend to scatter the
beam without any single strong reflection
Small interface produces scattering of
reflection
c) Texture and Size of Interface

24. Principle
Pulse- Echo System
Emission of multiple short pulses of ultrasound waves with
brief interval to detect, process and display the turning Echoes
ELECTRIC CURRENT
TRANSDUCER
US WAVE
SURFAC
E

25. Ophthalmic USG uses high-frequency sound waves
transmitted from a probe into the eye
 As the sound waves strike intraocular structures,
they are reflected back to the probe and converted
into an electric signal
The signal is subsequently reconstructed as an
image on a monitor

26. Emitted Sound Beam
 Used in A scan echography
 Beam has parallel border
Non-focused Beam Focused Beam
 Used in B scan
 Examination takes place in a
focal zone
 The beam is slightly diffracted

27. 1. Probe
 Consists of piezoelectric transducer
 Device which converts electrical energy to sound energy
[Pulse ] and vice versa [Echo]
 Basic Components :
Piezoelectric plate
Backing layer
Acoustic matching layer
Acoustic lens
Instrumentation

28. Piezoelectric Element
Essential part generates ultrasonic waves
Coated on both sides with electrodes to which a voltage
is applied
Oscillation of element with repeat expansion and
contraction generates a sound wave
 Most common: Piezoelectric ceramic ( Lead zirconate,
titanate)

29. Planer crystal
- Produce relatively parallel sound beam (A- Scan)
Acoustic lens
- Produce focused sound beam (B-scan)
- Improves lateral resolution
Shape of the Crystal

30. Backing Layer
(Damping material: metal powder with plastic or epoxy)
 Located behind the piezoelectric element
 Dampens excessive vibrations from probe
 Improves axial resolution
Acoustic Matching Layer
 Located in front of piezoelectric element
 Reduces the reflections from acoustic impedance between
probe and object
 Improves transmission

31. (longitudinal resolution or azimuthal resolution )
 Resolution in the direction parallel to the ultrasound
beam
 The resolution at any point along the beam is the same;
therefore axial resolution is not affected by depth of
imaging
 Increasing the frequency of the pulse improves axial
resolution
Axial Resolution

32.  Ability of the system to distinguish two points in the
direction perpendicular to the direction of the ultrasound
beam
 Affected by the width of the beam and the depth of imaging
 Wider beams typically diverge further in the far field and
any ultrasound beam diverges at greater depth, decreasing
lateral resolution
 Lateral resolution is best at
shallow depths and worse
with deeper imaging
Lateral Resolution

33. Receives returning echoes
Produces electrical signal that undergoes complex
processing
Amplification, Compensation, Compression,
Demodulation and Rejection
2. Receiver (computer unit)

34. Gain
Relative unit of Ultrasound intensity
Expressed in Decibel (db)
Adjust of gain doesn't change the amount of energy
emitted by transducer but change in intensity of the
returning echoes for display
Higher the gain – Greater the sensitivity of the instrument
in displaying weaker echoes (i.e Vitreous opacities)
Lower the gain – Weaker the depth of sound penetration
Terminologies

35. Acoustic impedance mismatch
- Resistance of tissue to passage of sound waves
- Difference of two tissues at the interface
Homogeneous (Vitreous)- Sound passes through tissue
with no returning signal
Heterogeneous (Orbital Fat) - Different levels of
acoustic impedance mismatch within tissue

36. Anechoic : No Echo
Attenuation : Sound is absorbed & scattered
Shadowing : Sound is strongly reflected, nothing passes
through it (drusen of optic nerve head, air)
Reverberation : Collection of Reflected sounds bouncing
back and forth between tissue boundaries
(foreign body in eyeball )

37. Indications of Ocular B Scan

38. Enophthalmos
Unilateral or Bilateral
Exophthalmos
Globe Displacement
Lid Abnormalities -Ptosis,
Retraction, Swelling, Ecchymosis
Palpable or Visible Masses
Chemosis
Motility Disturbances;
Diplopia
Pain
Indications of Orbital B Scan

39. Contraindications
 Obvious or suspected globe rupture
 Significant peri-orbital injuries
 Suspected clinically significant retrobulbar
hematoma

40. Display Modes
Modes
M-
Mode
A-
Mode
B-
Mode

41. 1. A-mode Display
 Time amplitude USG
 One dimensional acoustic display
 Tissue boundary
- displayed graphically as function of distance along a selected
axis
 Spacing of the spike
- time taken for the sound beam to reach the given interface
and its echo to reach the probe

42.  Amplitude of echo on the display is proportional to the
sound energy reflected at specific tissue boundary
 8 MHz
 Probe emits unfocused beam
The term “A-Scan” is often used to describe this
mode, but it is not an appropriate term, since the
transducer is fixed in one position during biometric
procedure and is not scanning

43. Uses
 Axial length measurements
 Intraocular and intraorbital pathologies
Detection
Differentiation
Localization

44. A-mode USG Biometry
 Axial length measurement
 To obtain the power of IOL
 Calculation of the total refracting power of the eye

45. Probe position
Just touch the cornea
Aligned with optical axis of eye
- aimed towards the macula
Corneal compression
- A 0.4mm compression causes 1 D error in the calculated
IOL power
- Contact Vs immersion method

46.  Tall echo – cornea, one peak – contact probe, double
peak – immersion probe
 Tall echoes – ant. & post. lens capsules
 Tall sharply rising echo – retina
 Medium tall to tall echo – sclera
 Medium to low echoes – orbital fat
A Scan Characteristics

47. 2. M-mode Display
Motion mode or time motion mode
Dilation and constriction of blood vessel
Accommodation fluctuation
Vascular pulsation in ocular tumor
Motion of detached retina
- PVD vs RD

48. 3. B-mode Display
Intensity modulated USG
B Stands for Brightness modulation
Presents a cross sectional or 2D image
True scanning
Probe emits focused beam
10 MHz
Each echo
o Represented as a dot on display screen
o Strength of the echo brightness of the dot

49. Normal B-scan
• Initial line on left: probe tip
• Right side: fundus opposite to
probe
• Upper part: portion of the globe
where probe marker is directed
Interpretation
 Based upon three concepts
 Real Time
 Gray Scale
 Three-Dimensional analysis

50. Real Time
 Images can be visualized at approximately 32 frames/sec,
allowing motion of the globe and vitreous to be easily
detected
 B scan allows real time evaluation of any ocular
pathology
 Real time ultrasonic information frequently aids in
vitreoretinal surgery

51. Gray Scale
 Displays the returning echoes as a 2D image
 Strong echoes are displayed brightly at high gain and
remain visible even when the gain is reduced
 Weaker echoes are seen as lighter shades of gray that
disappear when the gain is reduced
 Comparing echo strengths during examination is the basis
for qualitative tissue analysis

52. Three-Dimensional Analysis
 Developing a mental 3D image or anatomical map from
multiple 2D B-scan images is the most difficult concept
to master
 This is essential, because it provides
the vital architectural information that
is the basis for B-scan diagnosis
 Especially important in the preoperative evaluation of
complex retinal detachments and intraocular or orbital
tumors

53. Examination Techniques For The Globe-B
scan
Axial Transverse Longitudinal
Probe Orientations

54. Axial
Probe directly over cornea and directed axially
Pt. fixating in primary gaze
Posterior lens surface and optic nerve head are placed in
the centre of the echogram
Optic nerve head is used as an echographic centre section
Easiest to perform

55.  Mainly two varieties of axial scans
Horizontal axial scan
 Marker at 3 0’clock RE and 9 0’clock LE
 Macular region is placed just below the optic disk
Vertical axial scan
 Marker at 12 0’clock
 Macula is not seen in this scan
Oblique axial scan
 Marker always superior
 Sections of all other clock hours
can be performed

57. Points to be noted
 Higher decibel gain levels are needed to show structures at
the posterior segment
 Because of scatter and strong sound attenuation created by
the lens
- In pseudophakia strong artifacts created by the lens
implant hampers the adequate visualization
Significance
Easy orientation and demonstration of posterior pole lesions
and attachments of membranes to optic nerve head

58. Transverse
 EYE – looking in the direction of observer’s interest
 PROBE –parallel to limbus and placed on the opposite
conjunctival surface
 Probe Marker
superior (if examining nasal or temporal) or nasal(if examining
superior or inferior)
 6 clock hrs examined at a time
 Limbus-to-fornix approach is used to detect from posterior
pole to periphery
 Quadrant examination
 Gives lateral extent of the lesion

59.  The clock hr which the marker faces is always at the top
of the scan
 The area of interest in a properly done transverse scan
is always at the centre of the right side of scan
Nasal
Bridge

61. Longitudinal
 EYE - looking in the direction of observer’s interest
 PROBE – perpendicular to the limbus and placed on the
opposite conjunctival surface
 PROBE MARKER - directed towards the limbus
 Optic nerve shadow always at the bottom on the right side
 1 clock hr per time examination
 Determines the antero-posterior (axial) extent of the lesion
 Significance
- Best for peripheral tears and documentation of macula
Nasal
Bridge

63. Examination Procedure
Positioning the patient
Topical anesthesia
Techniques
Contact Technique
o Probe is placed directly
on the globe
Immersion Technique
oMethylcellulose - a
coupling medium (B-
Scan)

64. Sources of Error in contact technique
Corneal compression (Shorter Axial length)
- 1mm error in Axial length – 2.5 to 3.0 Ds error in IOL
Power
Misalignment of sound beam
Source of error in immersion technique
Small air bubbles in the fluid gives falsely long AL
measurement

65. Localization Of Macula
Macula
Localization
Vertical
Horizontal
Longitudinal
Transverse

66. Horizontal
Probe placed on the corneal vertex
Marker nasally (as with a horizontal axial scan)
The probe should be aimed straight ahead to center the
macula
The macula will be centered to the right of the
echogram, with the posterior lens surface centered to
the left

67. Vertical
Probe placed on the corneal vertex
Marker is in the 12-o'clock position
The nerve will not appear in these scans because this
is a vertical (instead of horizontal) slice of the macula

68. Transverse
Patient fixes slightly temporally
Probe on nasal sclera with marker at 12’o clock
Optic nerve as the centre of imaged clock macula is
at 9’o clock in right eye and 3’o clock in left
Bypasses the lens

69. Longitudinal
Probe held on sclera, bypassing crystalline lens
Optic nerve is seen at the bottom with macula just
above

70. Orbital Screening
Orbit highly reflective owing to heterogeneity of
orbital fat which produce large acoustic interface
B scan- bright zone
A scan- highly packed tall spike fading from left to right
 Three major portions
Orbital soft tissue assessment
Extraocular muscle evaluation
Retrobulbar optic nerve examination

71. Two Approaches
 Transocular (through the globe)
- For lesions located within the posterior & mid
aspects of the orbital cavity
 Paraocular (next to the globe)
- For lesions located within the lids or anterior orbit

72. Three methods: Axial, transverse & longitudinal
Transverse Longitudinal

73. A-SCAN B-SCAN
AMPLITUDE MODULATION SCAN. BRIGHTNESS MODULATION SCAN.
FREQUENCY OF ULTRASOUND IS 8
MHERTZ.
FREQUENCY OF ULTRASOUND IS 10
MHERTZ.
ONE DIMENTIONAL IMAGE OF
SPIKES OF VARYING AMPLITUDES
ALONG A BASELINE.
TWO DIMENTIONAL IMAGING OF
SERIES OF DOTS AND LINES THAT
FORM THE ECOGRAM.
EMITS UNFOCOUSED BEAM. EMITS FOCUSED BEAM.
PROVIDES QUANTITATIVE
INFORMATIONS.
PROVIDES TOPOGRAPHIC
INFORMATIONS.
IS A BASIS OF OCULAR BIOMETRY. ALLOWS REAL TIME EVALUATION OF
ANY OCULAR PATHOLOGY.

74. Anterior Segment Evaluation
Immersion
Technique
High Resolution
Technique

75. Immersion Technique
 Examining the anterior segment with a standard 10
MHz contact probe can be accomplished only with the
use of a scleral shell
 This shifts the anterior segment to the right and into
the area of focus of the sound beam, improving
resolution of anterior segment pathology
 The shell is filled with methylcellulose or some other
viscous solution to a meniscus, avoiding air bubbles
within the shell

76.  The probe is placed on top of the shell
 This produces an echolucent area on the left side of the
echogram corresponding to the shell and methylcellulose
 Diagnostic A-scan also can be performed through the shell,
directly over the lesion, for tissue differentiation.

77. Immersion B-scan image of
an iris melanoma extending
into the ciliary body
Modified immersionB-scan. Immersion

78. Immersion/normal
AC, anterior chamber;
C,cornea; F, fluid in scleral
shell; I, iris; L, lens.
Lens/cataract.
AC, anterior chamber;
arrow, lenticular opacities;
C, cornea; F, fluid; L, lens.

79. High Resolution Technique
Ultrasound biomicroscopy
Probes ranges from 20MHz to 50
MHz, with penetration depths of
about 10 mm to 5 mm respectively
The zone of focus is quite small
Scleral shell technique is used
Image quality far superior to
immersion technique
High-resolution B-scan images
of an iris melanoma

80. OCT vs UBM

81. Normal USG Characteristics
Lens : Oval highly reflective structure
Vitreous : Echolucent
Retina , Choroid , Sclera : Each is single highly
reflective structure
Optic Nerve : Wedge shaped acoustic void in
retrobulbar region
Extra ocular muscles : Echolucent to low reflective
fusiform structures
- The SR- LPS complex is the thickest, IR is the
thinnest
- IO is generally not seen except in pathological
conditions
Orbit : Highly reflective due to orbital fat

82. Normal B Scan

83. Topographic Echography
 Point-like e.g. fresh V.H
 Membrane-like e.g. R.D
 Mass-like e.g. choroidal melanoma
 Opacities produce dots or short lines
 Membranous lesions produce an echogenic line

84. Interpretations
And
Clinical Examples

85.  Fresh:
oDot-like: Echolucent or low reflectivity
 Old:
oMembrane-like: Varying reflectivity & dense
inferiorly
Fresh VH Old VH

86.  Multiple, densely packed, homogeneously distributed
echodense dots of medium to high reflectivity with a clear
preretinal space suggestive of Asteroid Hyalosis
 AH is highly ecogenic,they are still visible when the gain setting
is reduced upto 60dB whereas VH which usually disappears by
60 dB

87. PVD at high gain (90dB)
PVD (arrowheads) and
retina (arrow)
PVD at low gain (39 dB)
As the gain is reduced, the PVD
(arrowheads) disappears in contrast to the
retina (arrow), which remains visible even
at low gain settings

88. Posterior Vitreous Detachment

90. KISSING CHOROIDALS
 Smooth, dome shaped,
thick, less mobile with
double high spike
suggestive of Choroidal
Detachment

91. PVD RD CD
Topographi
c
Smooth, with or
without disc
insertion
Smooth or folded
with disc insertion
Smooth without
disc insertion
Quantitativ
e
< 100 % spike 100 % spike Double 100 %
spike
Kinetic Marked Moderate None

92. Differentiating Features of RD
Rhegmatogenous RD Tractional RD Exudative RD
Convex elevation ,
Undulating folds, PVR
Concave
elevation,Fibrous
tractional band
Convex elevation,
Shifting fluid changes
Configuration with
postural change

93. Total retinal detachment

95. PHPV: Longitudinal B-scan demonstrates taunt, thickened
vitreous band adherent to the slightly elevated optic disc

96. Globular/Oval echoic structure in posterior vitreous signifying
a Dislocated Lens

97. Retinoblastoma: Transverse B-scans demonstrate a large,
dome- shaped lesion with marked internal calcification

98.  Extremely thin IOFBs (< 100 mm) can be differentiated, localized
 Metallic IOFBs are echo dense—even at low gain settings—and
often produce shadowing of intraocular structures and the orbit

99. Transverse B-scan shows marked vitreous opacities and
membrane formation consistent with endophthalmitis

100. Panophthalmitis

101. Papilloedema
Transverse B-scan shows marked
elevation of the optic disc
Optic Disc Drusen
Longitudinal B-scan shows
highly calcified, round drusen
at the optic nerve head with
shadowing

102.  T sign collection of fluid in subtenon space suggestive of
Posterior Scleritis
 High reflective thickening of retinochoroid layer and sclera

103.  Posterior Staphyloma in High Myopia
 Shallow excavation of posterior pole
 Smooth edges

104. Anophthalmos Microphthalmos with cyst

105. Phthisis

106. Conclusion
 Knowledge about the anatomy, pathology and
ultrasound signs together with systemic and ocular
approach can provide useful diagnostic
information.

107. References
 Clinical Procedures in Optometry by J. D. Barlett, J. B.
Eskridge & J. F. Amos
 Ophthalmic Ultrasound: A Diagnostic Atlas by C. W.
DiBernardo & E. F. Greenberg
 Internet
 Previous presentations