What are FOUR clinical uses of Polarized Light?
- Haidenger Brush 2. Titmus Test 3. Polarized Microscope 4. Polarized Sunglasses
What is a Haidinger’s Brush?
It’s an entopic phenomenon seen when a polarizing filter is rotated in front of a blue background; looks like a propeller.
What is Polarized microscopy?
- Crossed polarizers in path of light - field looks black to observers.
- Object of interest placed between polarizers
- If object changes axis of polarization (BIREFRINGENCE) some light will get through and be visible to the observer.
What is Titmus stereo testing?
- Polarized lenses allow different images to pass to each eye
- Disparity between eyes converted to depth by brain.
What are FOUR applications of Interference?
- Antireflection coating 2. Interference filters (FA) 3. Interference fringe potential acuity device
What is INTERFERENCE?
Occurs when 2 light waves overlap.
Constructive vs Destructive
What is COHERENCE?
Ability of two waves to interfere with each other.
How does OCT use COHERENCE?
Use interference to detect change in coherence of light passing through the layers of the eye.
What is DIFFRACTION and give an example?
- Light waves bend (spread) slightly when they encounter an aperture.
- The smaller the aperture, the greater the diffraction
- Example: The pupil (Pupil aperture of less than 2.5 mm begins to limit acuity) and an AIRY DISC
What is SCATTERING and give an example?
- Light interaction with particles of similar wavelengths.
- BLUE scatters more (since SHORTER wavelength=higher scattering)
- Wider, irregular spacing or larger particles scatter all visible wavelengths
- Example: clouds, CORNEAL EDEMA; Asteroid Hyalonosis
What is REFLECTION and give an example?
- Ex: Asteroid Hyalosis
What is PIN HOLE Occluder and example of and how big is it?
- Diffraction
2. 1.2 mm - optimal size (balances effectiveness vs diffraction -diffraction occurs when PH <1.2)
What is the refractive index of water?
1.33
What is the refractive index of Aqueous?
1.336
What is the refractive index of vitreous?
1.34
What is the refractive index of cornea?
1.376
What is the refractive index of crystalline lens?
1.42
What is critical angle and what is an example?
Angle at which light is bent exactly 90 away from the normal.
Example: glass/air interface = 41 degrees.
What is total internal reflection and give examples?
- Angle of incidence exceeds the critical angle.
Example: Gonioscopy, fiber optics, indirect ophthalmoscope eye pieces.
YAG laser is a example of?
Photodisruption
Excimer laser is an example of?
Photoablation - carbon-carbon, carbon-nitrogen bonds are directly broken and tissue is vaporized.
Pinhole acuity is limited to what range of refraction?
-5 to +5
What is TEMPORAL coherence?
When one part of a beam of light is able to interefere with the same beam of light. This is how LASERS amplify their energy.
What is the refractive index of silicone?
1.438
