principle of ophthalmic ultrasound mainly B sacn

1. Ultrasound in Ophthalmology

2. • Safe
• Non – invasive
• Instant feedback
• Mostly useful in presence of opaque ocular
media

3. Basic physics
• Frequency - above the audible range of 20 kHz.
higher the frequency, more the resolution, lesser the
penetration
• Transducer - a piezoelectric crystal produses micro pulses
• Acoustic density
• At every interface, some of the echoes are reflected back
to the transducer, according to acoustic density.

4. • physical laws of acoustic energy:
reflection, refraction, and absorption.
• The angle of incidence
Needs to be directed perpendicular to the desired
structure.
oblique angle of incidence result in the reflection sound
beams causing a weaker signal.
• An irregular surface also causes loss of echo strength due to
reflection.

5. A-scan
• One-dimensional
• Vertical spikes correspond to acoustic density.
• Two types of A-scan
biometric
diagnostic

6. Biometric A-scan
• Optimized for axial length.
• Frequency used - 10–12 MHz and a linear amplification curve.
• The primary function – IOL calculation.

7. Standardized A-scan
• Frequency - 8 MHz and an S-shaped amplification curve - logarithmic
amplification and higher sensitivity.
• designed to scale acoustic density of retina 100% when the sound is
perpendicular. choroid and sclera also produce 100%
• Allows tumor cell structure to be evaluated and differentiated.
• In combination with B-scan, helps in the differentiation of
vitreoretinal membranes

8. B-scan
• Mostly contact
• Two-dimensional
• Display echoes using both the horizontal and vertical orientations to
show shape, location and extent.
• Strength of the echo is determined by the brightness.
• Mostly frequency is near by 10 MHz and uses logarithmic
amplification.

9. • evaluation of static B-scan images can lead to misdiagnosis. It is a
dynamic process requiring attention to the mobility of echoes.
• Three basic B-scan probe orientations are:
axial, transverse and longitudinal
immersion B-scan
• It is valuable in the evaluation of pathology near the ora - an area that
is too anterior for contact B-scan and too posterior for UBM (40 –
80Mhz)

10. Color Doppler ultrasonography
• Simultaneously allows B-scan and evaluation of blood flow.
• The red end of the spectrum - flow moving towards the transducer
and the blue end of the spectrum - flow is moving away.
• effective in the detection of ocular and orbital tumor vasculature,
carotid disease, central retinal artery and vein occlusions and non-
arteritic ischemic optic neuropathy

11. 3D ultrasonography
• Multiple consecutive B-scans are utilized to create a 3D block.
• The probe is held fixed, and serial images are rapidly obtained as the
transducer rotates.
• Useful in estimating the volume of intraocular lesions and for
evaluation of retro-bulbar optic nerve.

12. Axial resolution
• The axial resolution, is related to
frequency, piezoelectric crystal shape and the damping material
attached to the crystal.
• The damping material serves to shorten the pulses.
The shorter the pulse, the better the axial resolution.
• The concave shape of the crystal focuses the sound. The focused
sound increases not only axial, but also lateral resolution.

13. Amplification Curves
• The receiver processes echoes by
amplification, compression, compensation, demodulation and
rejection.
• Amplification –
linear, logarithmic or S-shaped
• Type of amplification curve affects the dynamic range - the range of
echoes that can be displayed (labeled in units dB).

14. • Linear curve amplifiers - small dynamic range, sensitive to minor
differences in the density
• logarithmic amplifiers - large dynamic range, lesser sensitive
• S-shaped amplifiers - offers the sensitivity of linear amplification
and the dynamic range of logarithmic amplification.

15. Gain
• The amplification of echoes are adjustable by adjusting the gain (dB).
• Lowering the gain :
decreases the depth of penetration and increases resolution.
• The choroid, sclera and orbital structures are usually best examined
at a low gain.

16. • At a high gain –
weaker echo sources are detected, but resolution is lost.
• Vitreous opacities and thin vitreous membranes are best examined at
high gain.
• Time gain compensation control (TGC)
Amplifies weaker echoes from deeper tissues more than those
from superficial, thus equalizing the echo strength from similar
tissues located at varied distances from the transducer.

17. patient preparation
• Ideally reclined position.
• Display and patient’s head should be parallel and in close proximity
• topical anesthesia
• methylcellulose-based gel as coupling agent
• both eyes be opened and gaze in the direction being imaged.
• B-scans through closed eyelids
1. Ultrasound waves are attenuated due to the soft eyelid
2. Difficult to determine the exact position of the probe on eye.

18. B-scan probe
• Have a marker along the side indicating the top of the display
• Probe tip - the white line on the far left side of display.
• Echoes to right of this line - ocular structures opposite the probe tip.

19. Probe Positions
• Transcorneal scans
Axial scans

20. • Sound attenuation and refraction - crystalline lens - diminished
resolution.
• Pseudophakic - intense sound reverberation echoes
• Evaluation of macula, Tenon’s space, and the optic nerve.
Para-axial scans
• Peripapillary fundus.
• Sound attenuation not as marked as with the axial scan.
• Peripapillary mass lesions

21. Trans-scleral scans
• Longitudinal and transverse
• Bypass the crystalline lens - better resolution
• Patients are more cooperative.
• The patient’s gaze should be directed in the direction of the area to
be examined.
• anatomical references - optic nerve and extra-ocular muscles.
• Posterior pole - The macula is only evident when thickened.
• Optic disc is used as the reference center of the posterior segment.

22. L
T

23. • Five scan screening - four transverse and one longitudinal B-scan - the
entire posterior segment can be well imaged.

24. Diagnostic features for assessing intraocular lesions.
Topographic Quantitative Kinetic
Location Reflectivity Mobility
Shape Internal structure Vascularity
Extent Sound attenuation Convection movement

25. Topographic ultrasonography
• To determine location, shape and extent of the lesion.
• A transverse scan performed first to determine the maximal height
and lateral basal dimension of the lesion
• A longitudinal B-scan is performed next to evaluate the anterior to
posterior topographic features of the lesion

26. Compilation of topographic B-scan images to differentiate membranes. Transverse B-scan
showing a slightly rope-like, elevated membrane. Corresponding longitudinal B-scan at the same
clock hour showing a V-shaped elevated membrane inserting into the disk. Mental compilation
of scans into a three-dimensional image differentiates membrane as an open funnel-shaped
retinal detachment.

27. Quantitative ultrasonography
• Reflectivity - height of the spike on A-scan.
A-scan probe sh’d be calibrated for tissue sensitivity
sound directed perpendicular to the lesion
Internal structure - homogeneous - little variation in spikes
heterogeneous - marked variation
• Sound attenuation (acoustic shadowing) - Calcification, foreign
bodies and bones

28. (reflectivity). Arrow represents the path of sound beam used to generate the A-
scan. Diagnostic A-scan of the solid fundus mass shows high reflectivity of the
retina (arrow) and low to medium internal reflectivity of the mass lesion
(arrowheads).

29. Sound attenuation. Transverse B-scan shows an irregularly shaped lesion with
highly reflective areas (arrow) causing shadowing of the orbital structures
(asterix).

30. Angle kappa - greater the attenuation of sound, greater the angle kappa

31. Kinetic ultrasonography
• motion of a lesion
• within a lesion - mobility, vascularity, and convection movement
Mobility
• change in gaze
• Posterior vitreous detachments, retinal detachment, and choroidal
detachments all exhibit distinctive patterns of mobility

32. Vascularity
• Fast, low-amplitude flickering
• Detected on both B-scan and A-scan.
• Probe and patient’s gaze are held stationary
• Graded mild, moderate, or marked, corresponding to the intensity

33. Convection
• Slow, continuous movement - secondary to convection currents -
blood, layered inflammatory cells, or cholesterol debris
• Probe stationary and the patient’s gaze fixated.
• Long-standing vitreous hemorrhage that has settled beneath a tight
retinal detachment.
• Differentiation of settled debris and or intraocular solid mass lesions.

34. Vitreo-retinal Disease

35. Fresh vitreous hemorrhage
showing diffuse low to medium
echoes
Pseudomembrane representing
the organization of blood
moderately dense vitreous
hemorrhage

36. Subhyaloid hemorrhage Layered vitreous hemorrhage
mimics retinal detachment

37. Vitreous hemorrhage in a
vitrectomized eye in high gain,
arrowheads – vitreous skirt
Same patient on low gain. VH is
not visible as it does not
organize in a vitrectomized eye.
Discontinuities vitreous skirt

38. PVD

40. Total open funnel RD. B-scan at low gain shows open funnel
configuration and optic disc attachment. A-scan shows 100%
peak corresponding to the RD S – sclera, V – vitreous, R –
retina.

41. Thin posterior vitreous
detachment (arrows) tent-like
tractional retinal detachment
(arrowheads).
multiple intraretinal macrocysts in a
chronic retinal detachment.

42. B-scan shows PVD (arrow), choroidal detachment (arrowhead), and
vitreous hemorrhage (VH). A-scan shows the characteristic double
peak on initial spike The probe must be perpendicular to see the
double peak

43. Serous choroidal detachment. Two
choroidal detachments with
echolucent subchoroidal serous fluid
(SF).
Hemorrhagic choroidal detachment.
“kissing” choroidal detachment with
dense opacities in the suprachoroidal
space indicative of hemorrhage (SH).

44. Retinal tear (T) with the edges of the
retina (arrowheads) folded
posteriorly. PVD (arrow) can be seen
connected to the folded retina.
Pigment epithelial detachment

45. Echographic elongation of the
vitreous cavity by silicone oil and
limited visibility of posterior ocular
structures
Following removal of silicone oil. few
droplets of oil that remain in the eye are
visible as highly reflective surfaces
(arrowheads) B – scleral buckle

46. Intra-ocular Tumor

47. Classic presentation of retinoblastoma. External photograph showing right-sided
leukocoria B-scan revealing an intraocular calcified mass

48. Diffrrential diagnosis of white reflex

49. Conditions associated with intraocular calcification
Retinal and retinal pigment epithelium (RPE) lesions
• Retinoblastoma
• Astrocytic hamartoma
• Chronic retinal detachment
• RPE metaplasia
• Cysticercosis

50. Choroidal lesions
• Choroidal osteoma
• Sclerochoroidal calcification
• Choroidal granuloma
Others
• Optic nerve head drusen
• Scleral calcification (Cogan’s plaque)
• Phthisis bulbi

51. Persistent fetal vasculature (PFV). Taut,
thickened vitreous band adherent to the
slightly elevated optic disc

52. Circumscribed choroidal hemangioma. Axial B-scan showing dome-shaped mass
OCT shows anterior bowing of the retina due to underlying choroidal
hemangioma but the retinal architecture is normal

53. B-scan demonstrating that nevus less than 1 mm height. A-scan with
high internal reflectivity. OCT showing minimal choroidal thickening and
drusen

54. Choroidal melanoma. Clinical photograph showing large, partially amelanotic
dome-shaped choroidal mass. B-scan reveals a mushroom-shaped choroidal mass
that has broken through Bruch’s membrane (arrows) touching the posterior
surface of the lens

55. Choroidal melanoma with extrascleral extension. A-scan shows medium to high
internal reflectivity of the choroidal lesion (arrows–A) and high internal
reflectivity of the extraocular extension (arrows–B)

57. Astrocytic hamartoma. Clinical photograph of peripapillary calcified astrocytic
hamartoma. B-scan demonstrating calcification near optic disc (arrow).

58. Choroidal metastasis. B-scan demonstrating a total retinal detachment, diffuse
choroidal thickening (arrowheads), and extraocular extension (arrows) near the
retrobulbar optic nerve

59. juxtapapillary
choroidal
osteoma (A).
B-scan shows
calcification with
shadowing.
A-scan - high internal reflectivity (C). OCT (D) reveals thickened retina presence of
a subretinal neovascular membrane and faint outline of the choroidal osteoma

60. Occular Inflammatory Diseases

61. Ant. Vitritis Mild to moderately dense, vitreous opacities anterior to the posterior
vitreous detachment (arrows) and very mild subhyaloid opacities

62. B-scan in a patient with chronic uveitis at a low gain showing marked thickening
of the macular area (arrowhead) and moderate scleral thickening with a thin
band of low reflectivity in Tenon’s space (arrow) OCT of the macular area in the
same patient showing marked macular elevation with cystic spaces

63. Toxocariasis. Transverse B-scan demonstrating a taut membrane extending
across the vitreous and adherent to an irregularly shaped, highly reflective
granuloma that is causing shadowing of the orbit (arrowhead).

64. Toxoplasmosis. Marked vitreous haze with toxoplasmosis lesions of the fundus. B-
scan at a low gain demonstrating a posterior vitreous detachment (arrowhead)
and a dome-shaped, elevated lesion of the fundus (arrow).

65. Vogt–Koyanagi–Harada syndrome. Axial B-scan showing marked choroidal
thickening (arrow) and a serous retinal detachment (arrowhead).

66. Axial B-scan at a low gain showing
marked thickening of the posterior
fundus (arrows).
Transverse B-scan at a high gain showing
dense, clumped vitreous opacities
adjacent to the thickened choroid
(arrows)

67. B-scan demonstrating marked, diffuse
thickening of the posterior fundus and
sclera (arrows) with a thin band of low
reflectivity in Tenon’s space (black
arrows) indicative of posterior scleritis.
Diagnostic A-scan showing highly
reflective thickening of the posterior
fundus and sclera

68. bullous choroidal detachments (arrows) with moderate, clumped opacities
beneath on transverse B-scan of the peripheral fundus and corresponding fundus
photograph

69. “T-sign” in posterior scleritis. Axial B-scan shows posterior scleral thickening and low reflective infiltrate behind the
peripapillary sclera and optic nerve creating the classical “T-sign” (arrows). Axial B-scan showing marked thickening
of the sclera with only a very thin band of low reflectivity behind the peripapillary sclera (arrows).

70. Endophthalmitis. Transverse B-scan showing marked membrane formation
(arrow) throughout the vitreous space and marked, irregular fundus thickening
(small arrows)

71. Orbital myositis. External photograph demonstrating exotropia of the left eye. B-
scan shows marked enlargement of the medial rectus muscle (arrow) and its
inserting tendon (small arrow),

72. Optic Nerve Diseases

73. Large optic disc cup. B-scan demonstrates corresponding
concave bowing of the optic disc.

74. Normal retrobulbar optic nerve measurements
• Measured in two locations
• 3 mm posterior to the nerve head and
• as close as possible to the orbital apex
• Normal - 2.2 to 3.3 mm - variation can occur
• A difference of ≥0.5 mm may indicate an abnormal thickness in one
• No significant changes when measured in Trendelenburg or reverse
Trendelenburg position as compared with the supine position

75. Papilledema
30° test
• Increased subarachnoid fluid can be differentiated from thickening of
the parenchyma or perineural sheaths
• perineural sheaths measured anteriorly and posteriorly
• In primary gaze
• 30° lateral gaze
• A decrease in diameter of >10% in lateral gaze - a positive 30° test -
increased subarachnoid fluid.

76. Papilledema. Fundus photographs (A, right eye; B, left eye) show marked elevation of the optic disc that obscures
clarity of the retinal vessels at the optic disc nerve head margin (arrowhead).

77. Transverse B-scan - marked
elevation of the optic disc.
a cross section of the retrobulbar optic
nerve and crescent-shaped echolucent
area behind the nerve indicative of
increased subarachnoid fluid

78. Positive 30° test with diagnostic A-scan while the eye is in primary gaze with an
enlarged retrobulbar optic nerve (4.8 mm) When the eye is fixated 30° laterally, a
marked decrease in the size of the retrobulbar optic nerve (3.5 mm)
4.8 3.5

79. • Blaivas performed a prospective observational study on patients
suspected of having raised ICT (adults)
• Patients having raised ICT were predicted correctly by optic nerve
sheath diameters of >5 mm.
• The ultrasonographic measurements were correlated more closely to
the intracranial pathology than the clinical examination.
• Mean optic nerve sheath diameter for those not meeting CT criteria
for raised intracranial pressure was 4.4 mm.

80. • Kimberly also correlated optic nerve sheath diameters with directly
measured intracranial pressure
• In an adult, optic nerve sheath diameters >5 mm correlated with
intracranial pressure >20 cmH2O, with sensitivity of 88% and a
specificity of 93%.
• In children sheath diameter of greater than 4 mm in infants and of
greater than 4.5 mm in children age 1 to 15 years should be
considered abnormal.

81. Buried optic nerve head drusen. Fundus photograph shows optic nerve head
elevation and absence of optic cup mimicking papilledema.
B-scan shows highly calcified, round drusen at the with shadowing
Diagnostic A-scan shows normal retrobulbar optic nerve diameter measuring 3.2
mm
Pseudopappiledema
3.2

82. Optic disc coloboma. Fundus photograph and Longitudinal B-scan. Note
vitreous hemorrhage, a shallow retinal detachment (arrow) and coloboma at
the inferior portion of the optic nerve head (arrowhead)

83. Fundus photograph showing congestion and elevation of the right optic disc
Normal contralateral left optic disc

84. Diagnostic A-scan shows thickening
of right optic nerve with retrobulbar
diameter of 4.50 mm. 30° test was
negative for subarachnoid fluid
A-scan of normal left optic nerve with
retrobulbar diameter of 2.32 mm
4.5 2.3

85. B-scan right showing enlargement of optic nerve and Coronal MRI (T1 fat
suppression) showing thickening and enhancement of optic nerve sheath with
compression of optic nerve.