AB scan technique

A-scan Technique

Positioning the probe:-

Principle:

Anesthesia

Touch cornea

A-scan
Immersion Techniques

How does an A- scan become a B- scan

A-scan is a time amplitude. The first structure the sound wave hits is the cornea, thus generating the first spike. Then tow spikes for anterior and posterior len capsules. There is no spike in the normal clear vitreous. And then spikes for the retina and choroid and sclera posteriorly.

Hundred of A scans are aligned together along the posterior retina and then taken at 90 degrees. By joining the dots and 2D B-scan is generated.

The vector line: represents the one A-scan, at that position, that is displayed at the bottom of the screen.

A- scan Vector line

It represents the one A- scan, in that site, at that position,
that is displayed at the bottom of the screen

The greater the perpendicularity, the more steeply rising the spike is from baseline and the higher the spike.

B- scan Technique

Positioning the probe:

Probe mark
Gel
Eyelid (beginners)
Image structures inside
Probe Mark (upper screen)
Other side of probe (screen bottom)
Tilt probe
Examine all quadrants
Probe position

Identify the probe mark (dot or line).
Put sterile gel.
Put probe on upper eyelid (no need for anaesthesia).
You can identify structures (vitrous, retina, choroid, fat, muscle)
Probe mark represent top of screen (echogram), other side represent the lower screen.
Tilt probe forward and backward to see about 6 cock hours.
This shows the inferior view of retina.
Repeat for all quadrants.

Anaesthetize eye if using conjunctival approach.

Put Gel.

Locate probe mark .

It always represents upper screen.

Orientation of probe

vTransverse

The mark is at the side of the probe.
Mark is either superiorly or nasally.

vLongitudinal

The mark is pointing toward the limbus.

Transverse position

(Parallel) to limbus

Longitudinal position

(Perpendicular) to limbus

Transverse position (Parallel) to limbus

Mostly used position beside axial scan. Basic screeing.

Right eye. Patient looks down.

Probe in superior limbus.

Mark: nasally, horizontally.

Locate optic nerve.

Scan inferior retina.

Lateral extent of pathology

Repeat for other gazes.

It demonstrate the lateral extent of the pathology.
Inferior retina (infero-nasal and infero-temporal).

Home madeB-scan

LE (O.N. nasal)
Inferior retin
Transverse position

Transverse position (Parallel) to limbus

Patient looks nasal.

Probe in lateral limbus.

Mark pointing superiorly (Vertical position).

Locate optic nerve.

Sweep probe horizontally to see nasal retina.

6 clock hours

It encompases 6 clock hours (3 clocks above lesion and 3 clocks below lesion).
E.g. superior mark pointing at 12 O’clock represent (3 O’clock at center of echogram, 12 O’clock at top and 6 O’clock at bottom).
To see supero-nasal and infero-nasal retina.
Sweeping from limbus to fornix allows examination from posterior pole to periphery (anteriorly).