Date post: | 23-Jan-2018 |
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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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