A scan ultrasonography

A Scan Ultrasonography - Basic for Lens

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

2. 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.

3. Instrumentation Pulser Reciever Display System

4. A Scan Mode

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

6. 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.

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

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

9. 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

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

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

12. KINETIC ECHOGRAPHY

13. Common Ocular Pathologies VITREOUS FLOATER VITREOUS HAEMORRHAGE

14. ENDOPHTHALMITIS POSTERIOR VITREOUS DETACHMENT

15. RETINAL DETACHMENT Intra Ocular Lens

16. CHOROIDAL MELANOMA CHOROIDAL HEMANGIOMA METASTATIC CARCINOMA

17. RETINOBLASTOMA CHOROIDAL DETACHMENT

18. DISLOCATED LENS INTO VITREOUS APHAKIC EYE

19. CONTACT TECHNIQUE

20. IMMERSION TECHNIQUE

21. I mmersion B-scan/vector A-scan technique

22. 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

23. 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

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

25. MISALIGNMENT SILICON OIL GLOBE