The document presents an in-depth overview of ophthalmic ultrasonography, including its historical development, principles, and clinical applications in ophthalmology. Key topics discussed include A-scan and B-scan techniques, advantages of using ultrasound in eye examinations, and the physics underlying ultrasound wave behavior. It also covers the factors influencing echo generation, various imaging techniques, and the instrumentation used, alongside indications for use and common sources of error in procedures.

1. Maharajgunj Medical
Campus, Nepal
Bikash Sapkota
B. Optometry
16th 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.  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
DEFINITION

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
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

8. 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
8

9. 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

10. 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

11. 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

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

13. 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

14.  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

15. 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

16.  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

17. ECHOLOCATION

18. 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

19. 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

20. ANGLE OF INCIDENCE
 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

21. INTERFACE
 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

22.  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
TEXTURE AND SIZE OF
INTERFACE

23. 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
SURFA
CE

24.  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

25. EMITED SOUND BEAM
NON-FOCUSED BEAM
 Used in A scan echography
 Beam has parallel border
FOCUSED BEAM
 Used in B scan
 Examination takes place in a
focal zone
 The beam is slightly diffracted

26. 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
INSTRUMEN
TATION

27. 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)

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

29. 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

30. Axial Resolution
(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

31. Lateral Resolution
 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

32. RECEIVER (computer unit)
 Receives returning echoes
 Produces electrical signal that undergoes complex
processing
 Amplification, Compensation, Compression,
Demodulation and Rejection

33. 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
TERMINOLO
GIES

34. 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

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

36. Indications of Ocular B Scan

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

39. DISPLAY
MODES
Modes
M-
Mode
A-
Mode
B-
Mode

40. 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
 Amplitude of echo on the display is proportional to the sound
energy reflected at specific tissue boundary
 8 MHz
 Probe emits unfocused beam
40
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

41. USES
 Axial length measurements
 Intraocular and intraorbital pathologies
 Detection
 Differentiation
 Localization

42. A-MODE USG BIOMETRY
 Axial length measurement
 To obtain the power of IOL
 Calculation of the total refracting power of the eye

43. 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
43

44. 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

45. 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

46. 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
oRepresented as a dot on display screen
oStrength of the echo brightness of the dot

47. 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

48. 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

49. 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

50. 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

51. EXAMINATION
TECHNIQUES FOR THE
GLOBE-B SCAN
Axial Transverse Longitudinal
Probe Orientations

52. 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

53.  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

55. 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

56. 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

57.  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

59. 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

61. 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)

62. 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

63. LOCALIZATION OF
MACULA
Macula
Localization
Vertical
Horizontal
Longitudin
al
Transverse

64. 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

65. 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

66. 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

67. LONGITUDINAL
Probe held on sclera, bypassing crystalline lens
Optic nerve is seen at the bottom with macula just
above

68. 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

69. 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

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

71. 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.

72. ANTERIOR SEGMENT
EVALUATION
Immersion
Technique
High Resolution
Technique

73. 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

74.  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.

75. Immersion B-scan image of an iris
melanoma extending into the ciliary body
High-resolution B-scan images of
an iris melanoma.

76. 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

77. OCT vs UBM

78. 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

79. 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

80. INTERPRETATIONS
AND
CLINICAL EXAMPLES

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

82.  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

83. 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

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

85. PVD RD CD
Topographi
c
Smooth, with or
without disc
insertion
Smooth or folded
with disc insertion
Smooth without
disc insertion
Quantitati
ve
< 100 % spike 100 % spike Double 100 %
spike
Kinetic Marked Moderate None

86. 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

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

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

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

90.  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

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

92. 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

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

94.  Posterior Staphyloma in High Myopia
 Shallow excavation of posterior pole
 Smooth edges

95. 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