Optics Ant. Seg. Imaging Flashcards
As a sound source vibrates, it creates regions of high pressure known as ____________.
Compressions
Where particles are pushed together.
As a sound source vibrates, it creates regions of low pressure known as ____________.
Rarefactions
Where particles are pulled apart.
Ultrasonography uses ___________ sound waves.
High-frequency
Ultrasonography is generated by ______________ acting as emitter.
Piezoelectric element
Biometry is important when planning in what surgery?
Cataract
Application of an electrical current to Piezoelectric crystals causes it to vibrate and generate ___________.
Ultrasound waves
Reflected sound waves hit the piezoelectric crystals causing it to vibrate and generate electrical current that is analyzed by _____________.
Ultrasound machine
Average sound velocity in the cornea.
1641 m/s
Average sound velocity in the Lens.
1641 m/s
Average sound velocity in the Aqueous humor.
1532 m/s
Average sound velocity in the Vitreous humor.
1532 m/s
Average sound velocity in a Phakic eye.
1550 m/s
Average sound velocity in an Aphakic eye.
1532 m/s
Average sound velocity in a Psuedophakic eye.
1532 m/s + correction factor for IOL material
A-Scan, A = __________.
Axial
A-Scan provides a _______ dimensional depth plot.
1-D
With A-Scan, time of flight is converted to ________.
Distance
Axial distances in A-Scan are plotted along the ____________.
X-axis
Amplitude of the reflected wave is the ________ axis in the A-scan.
Y-axis
A high-quality contact A-Scan of a Phakic eye consists of:
5 high-amplitude spikes
Steeply rising retinal spike and resolution of separate retinal and scleral spikes.
A-Scan and axial resolution is wavelength dependent. Smaller wavelength = __________ resolution.
Better
Why does Ultrasonography require physical contact and a gel/liquid?
Because of the strong air-corneal reflection signal.
Immersion coupling significantly reduces the __________ reflection signal.
Air-cornea
Immersion coupling causes the spike separation of?
Probe and cornea
With immersion coupling how does the corneal spike appear?
Demonstrates 2 small peaks, representing the epithelium and endothelium.
Is immersion coupling more accurate than contact biometry?
Yes
Is the cornea compressed with immersion coupling?
No
Eyes measured by immersion coupling method are _________ mm longer than with contact method.
0.1-0.3 mm
Is immersion coupling a slower or faster method than contact technique?
Faster
With probe orientation to visual axis, when will the spikes produced be maximum?
When the probe/sound beam is incident parallel and coaxial to the visual axis.
If the probe is oriented obliquely to the visual axis, how will this affect the spikes produced?
Spikes will be compromised.
How would a smooth macula affect spike amplitude?
Cause a high amplitude spike.
How would an irregular macular surface affect spike amplitude?
Cause lower amplitude spikes.
Mediums that have greater densities such as a cataract, can affect absorption and cause produced spikes to appear in what way?
Spikes that have less amplitude.
How can Corneal compression affect ACD measurement in A-Scan?
Compression can cause ACD to appear as if it is shallower.
How would high myopia and posterior staphylomas affect A-Scan measurement?
Sloped retinal surface, poor retinal spike, variable readings.
Gain is the _________ of the ultrasound signal.
Amplification
Higher gains = ________ amplitude and __________ resolution.
Increased amplitude
Poor resolution.
Would an Aphakic eye require less gain or more gain to be used?
Less gain
When gain is too high, the retina and sclera appear as a __________ spike with a ________ peak.
Thickened spike with a wide flattened peak.
Ultrasound produces ______ - _____ MHz sound waves.
8-20
Is ultrasound a contact method?
Yes
Does ultrasound provide a 2-D map?
No, 1-D
Is ultrasound reliable peripherally?
Not reliable peripherally.
Is ultrasound accurate for edematous corneas?
No
Pros of ultrasonography
Penetrates through opaque ocular media, portable, fast, simple, common clinically.
Cons of ultrasonography
Repeatability, not reliable peripherally, risk of corneal abrasion, requires contact.
Acoustical modalities require ____________.
Immersion coupling (contact method)
Do Optical modalities require contact?
No, does not require immersion coupling.
In Optical Low-Coherence Reflectometry, time of flight is measured by _________.
Interferometry
Interferometry uses __________ to extract information.
Interference of waves
Low-coherence interferometry uses light with a short coherence length instead of a __________.
Laser (high-coherence)
With Optical Low-Coherence Reflectometry, is there potential for sublayer pachymetry?
No, limited potential if any.
UBM
ultrasound biomicroscopy (B-Scan)
B-scan provides a _________ dimensional plot.
2-D plot
Primary use of A-Scan.
Distance/thickness measurement.
Primary use of B-Scan.
Structural imaging.
Resolution is dependent on ____________.
Wavelength
The higher the frequency the better the ___________.
Resolution
High gain = _________ signals displayed.
Weaker
Low gain causes ________ signals to disappear and allows for ?
Weak signals to disappear and allows for better resolution of strong signals.
What is the correct frequency to use for B-Scan when evaluating the anterior segment?
25-50 MHz
What is the correct frequency to use for B-Scan when evaluating the Posterior segment?
15-20 MHz
What is the correct frequency to use for B-Scan when evaluating the orbit?
10 MHz
Longitudinal B-Scan.
Probe marker is placed perpendicular to the limbus at any clock hour.
Axial B-Scan.
Sound beam directed such that it passes through the center of the lens and intersects the Optic Nerve.
Transverse B-Scan.
Probe marker parallel to the limbus at any clock hour.
UBM employs ultra-high frequency which allows for better resolution at the ____________.
Anterior chamber
UBM uses a probe stylus and requires ___________ and _____________.
Immersion coupling and applanation.
UBM provides better resolution at the expense of ________.
Penetration
Is UBM suitable for detailed corneal pachymetry?
Yes
How does Arc-Scanning Ultrasound work?
Moves in an arc, perpendicular to the curvature of the anterior ocular surface to map the corneal layers.
Confocal microscopy uses a laser to excite _________________
Fluorescence from fluorophores.
Confocal microscopy uses a dichroic mirror that does what?
Reflects certain wavelengths of light while transmitting others.
5 parts of Confocal Microscopy.
- Laser Excitation Source
- Fluorescence Dichroic Filters
- Pinhole
- Stepper Motors
- Objective
The Pinhole is an essential component of confocal setups as it acts as a spatial filter by preventing any light that is not ___________ to the objective focal plane from interfering with the image.
Confocal
With Confocal Microscopy, long working distances are required for __________ specimens and __________ imaging/optical sectioning.
Thick specimens and 3D imaging/optical sectioning.
Confocal microscopy helps to maintain tight focus through ___________ structures.
Corneal
Confocal microscopy has high-resolution with _______________.
Sublayer pachymetry.
Does Confocal Microscopy cause good penetration of opacities?
No, slow and poor penetration of opacities.
