A Scan Ultrasonography - Basic for Lens

1. A Scan Ultrasonography
Presenter : Dr Samuel Ponraj
Moderator : Dr PRR

4. Physics of Ultrasound
• Ultrasound passes through the tissue , part of the
wave is reflected back towards the probe
• Echoes formed at -- acoustic interfaces that are
created at the junction of media with different
sound velocities.
• The greater the difference in sound velocities of
the media at the interface, the stronger is the
echo.

5. Instrumentation
• Pulser
• Reciever
• Display System

7. A Scan Mode

8. GAIN
Highest gain widest sound beam
Highest penetration Max Spike Height
(Visualisation of Weak Signals)-PVD,Vitreous Opacities
LOWEST GAIN WEAKEST PENETRATION
DECREASED SPIKE HEIGHT (RETINA , SCLERA )

9. Indications
• To detect ,measure and differentiate tumours
and follow up.
• Biometry for accurate Axial length
measurement for IOL calculation.
• Morphological characteristics – AC depth,
Corneal thickness,Lens thickness and relative
position.

10. ADVANTAGES
• Easy to use
• No Ionizing radiation
• Excellent Tissue Differentiation
• Cost Effectiveness

11. Interpretation
a: Initial spike (probe tip and cornea)
b: Anterior lens capsule
c: Posterior lens capsule
d: Retina
e: Sclera
f: Orbital fat

14. Topographic Echography
Category Point-like Membrane-like Space-occupying
Echogram Single spike Single spike or
chain of spikes
Chain of Spikes
Differential
diagnosis
Foreign body Retinal
detachment
Melanoma
Vitreous opacities Choroidal
detachment
Retinoblastoma
Vitreous
membranes
Hemangioma
Tumor surfaces Vitreous
Haemorrhage
Assessment of shape, location and elevation of lesions

15. Quantitative Echography
1. Internal Structure Reflectivity
(Size & Arrangement of interfaces)
- Regular low – Melanoma
- Regular High – Haemangioma
- Irregular – Metastatic Carcinoma

16. 2. SOUND ATTENUATION
Scattering,absorption or reflectivity of
Sound energy
Steeper the Kappa
angle
Greater the Sound
attenuation
(Bone, Foreign Body)

17. KINETIC ECHOGRAPHY
Kinetic Echography
(Low gain)
Spontaneous
movements
(Stationary eye ) –
vascular lesion
After movements
{ Following Cessation of
Eye Movements }
- PVD,RD

18. Common Ocular Pathologies
VITREOUS
FLOATER
VITREOUS
HAEMORRHAGE

19. ENDOPHTHALMITIS
POSTERIOR
VITREOUS
DETACHMENT

20. RETINAL
DETACHMENT
Intra Ocular Lens

21. CHOROIDAL MELANOMA
CHOROIDAL HEMANGIOMA
METASTATIC CARCINOMA

22. RETINOBLASTOMA
CHOROIDAL
DETACHMENT

23. DISLOCATED LENS INTO
VITREOUS
APHAKIC EYE

24. CONTACT TECHNIQUE

26. IMMERSION TECHNIQUE

27. Immersion B-scan/vector A-scan
technique

28. Adjustments to UltraSound Velocity
settings
OCULAR
MEDIA
ULTRA SOUND
VELOCITY
THICKNESS CORRECTION
FACTOR
CORNEA 1641 M/SEC +0.55 +0.04 mm
AQUEOUS 1532 M/SEC
LENS 1628 + 4.72 +0.28 mm
VITREOUS 1532 M/SEC
TRUE AXIAL LENGTH = AAL 1532 + 0.04 mm + 0.28 mm
= AAL 1532 + 0.32 mm

29. COMPARISON BETWEEN CONTACT
TECHNIQUE AND IMMERSION
TECHNIQUE OF BIOMETRY
Contact technique Immersion technique
Patient is in a more comfortable
position, sitting
Patient is in a supine or reclining
position
Variability from one test to next is
present due inconsistent corneal
compression
No variability since probe does not
come in contact with cornea
Axial length measured is shorter by
an average of 0.24 mm
Axial length measured is closer to
the true value

30. Limitations and Pitfalls
• Multiple Artifacts
• Attenuation Artifacts
• Low reflective Spike
• Small tumours with False Negatives
• Intraocular foreign body
• Contact technique problem
• Misalignment

31. MISALIGNMENT
SILICON OIL
GLOBE