Ultrasonography of eye

Ultrasonography of eye

By Dr Nikita Jaiswal

2nd year resident

Glossary

O Introduction

O Terminologies

O Probe Positions

O Interpretations

Introduction

O B scan ultrasonography also known as

(brightness scan).

O It utilizes high frequency sound (10-

20Mhz) from a peizoelectric crystal

emitter/receiver that penetrates the tissue

& bounces back.

ULTRASOUND:O It is an acoustic wave that consists of an

oscillation of particles within a medium.

O Ultrasound waves have frequencies greater than

20kHz(i.e. 20,000oscillations/sec).

O Ophthalmic ultrasound is in the range of 8 to 10

MHz

O 1 megahertz=10,00,000 cycles/sec

HistoryO 1956- Mundt & hughes

O 1958-Baum & greenwood

O 1960- Jansson & associates

O In 1960’s ossoing emphasized on standardised

instrumentation ophthalmologist

During examination, the following systematic approach

is

universally recommended:

1. Screening for lesion detection: A+ Bscan.

2. Topographic examination for shape, border, location andextension (if possible) of the lesion: Bscan.

3. Quantitative Echography to know the reflectivity, soundattenuation & internal structure of lesion. It helps indetermining the texture of the lesion: Ascan.

4. Kinetic echography provides information about themobility, aftermovement and vascularity (Valsalvamanoeuvre) on Bscan. It also includes colour Dopplerassessment for blood flow.

Ultrasound Frequency

Abdominal 2-5 MHz

B scan 10 MHz

UBM 20-50 MHz

Media speed

cornea 1641 m/s

Aqueous humor 1532 m/s

lens 1641 m/s

Vitreous humor 1532 m/s

Silicone oil 990 m/s

INDICATIONS:-

O 1.Evaluation of intraocular details obscured

from visualization

by the ocular media opacities.

O 2. Evaluation of retinochoroidal lesions

especially tumors even

with clear media.

3. Differentiation of solid from cystic and

homogenous from

heterogeneous masses.

4. Examination of retrobulbar soft tissue masses and

normally

present orbital structures (to differentiate proptosis

from

exophthalmos).

5. Identification, localization and measurement of

non radioopaque/

radio-opaque foreign bodies. Assessment of

collateral damage in trauma cases.

6. Biometry .

7. Follow up evaluations

Terminologies

O Reflectivity: sound which is emitted by the

probe gets reflected back at the interface

between two media

O Ex: Aqueous & lens, vitreous & retina

forms an echo.

The greater the diff in density between the

structures, the greater will be its echo.

ANGLE OF INCIDENCE: the probe must always be placed

perpendicular to the area of interest to receive greater amount of

signals preventing dissipation.

ABSORPTION: when the ultrasonic waves encounter a dense

medium.,part of its gets reflected & part of it gets absorbed ,greater

the density greater will be absorption.

GAIN: It does not alter the frequency of sound or its velocity but

only changes the display pattern on the screen.

HIGHER GAIN=weaker signal gets dispalyed

LOW GAIN=only the structures with higher reflectivity gets

displayed.

PROBE POSITIONING:

O Transverse

O Longitudinal

O Axial

PROBE:O It has a transducer that moves rapidly back &

forth near the tip.

O Tip of the probe is oval in shape.

O Each probe has a marker.

O Methylcellulose is used as the coupling agent.

O Place to be placed: conjunctiva /cornea

O Over the eyelids it can be placed but avoided.

Bscan probes are thick, with a mark and emit

focussed sound beam at a frequency of 10MHz. Pictures obtained

with Bscan probe are two dimensional as compared to Ascan

probe.

The mark on the Bscan probe indicates beam orientation so that

the

area towards which the mark is directed appears at the top of the

echogram on display screen. Bscan probe can also be put directly

on

the anaesthetized globe after applying eye speculum; but mostly

the

Bscanning is done transpalpebrum with slightly increased overall

gain.

PROBE ORIENTATIONS:

O Transverse

O Longitudinal

O Axial

TRANSVERSE

Transverse section: The mark is kept parallel to

the limbus and probe

is shifted from limbus to the fornix and

also sideways. This scan gives

the lateral extent of the lesion

Longitudinal section: The mark is kept at right angle to the limbus to

determine the antero-posterior limit of the lesion.

Axial section: The patient fixates in the primary

gaze and the probe is

placed on the globe and directed axially. Depending on

the clock hour

location of the marker, axial-horizontal, axial-vertical

and axial oblique

pictures are obtained. These sections demonstrate

lesions at

the posterior pole and the optic nerve head.

3-Limbus 9-Posterior3-Equator 9-Equator3-Fornix 9-Anterior6-Limbus 12-Posterior6-Equator 12-Equator6-Fornix 12-Anterior

Probe position Area screened

INDICATIONS:

O MEDIA OPACITY:

LID ODEMA

CORNEAL OPACITY

KERATO PROSTHESIS

HYPHAEMA

HYPOPYON

SMALL PUPIL

PUPILLARY MEMBRANE

DENSE CATARACT

DENSE VITREOUS HAEMORHAGE

DENSE VITREOUS EXUDATES.

OTHERS:

O Differentiation of serous/haemorrhagic choroidal

detachment.

O Differentiation of rhegmatogenous/exudative

retinal detachment.

O Differentiation of iris from a ciliary body lesions.

O Differentiation of intraocular tumors.

Evaluation:

O Vitreous

O Retina

O Choroid

O Optic nerve

S/O OF PVD

POSTERIOR STAPHYLOMA

CHOROIDAL COLOBOMA WITH RETINAL

DETACHMENT

POST. DROPPED NUCLEUS

OPTIC DISC DRUSEN

Cystecercosis with retinal tear

Post dislocated IOL.

Calcified retinoblastoma

Air in the antetrior

chamber

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