Physical Optics

Question 1

What are FOUR clinical uses of Polarized Light?

Answer 1

1. Haidenger Brush 2. Titmus Test 3. Polarized Microscope 4. Polarized Sunglasses

Question 2

What is a Haidinger’s Brush?

Answer 2

It’s an entopic phenomenon seen when a polarizing filter is rotated in front of a blue background; looks like a propeller.

Question 3

What is Polarized microscopy?

Answer 3

1. Crossed polarizers in path of light - field looks black to observers.
2. Object of interest placed between polarizers
3. If object changes axis of polarization (BIREFRINGENCE) some light will get through and be visible to the observer.

Question 4

What is Titmus stereo testing?

Answer 4

1. Polarized lenses allow different images to pass to each eye
2. Disparity between eyes converted to depth by brain.

Question 5

What are FOUR applications of Interference?

Answer 5

1. Antireflection coating 2. Interference filters (FA) 3. Interference fringe potential acuity device

Question 6

What is INTERFERENCE?

Answer 6

Occurs when 2 light waves overlap.

Constructive vs Destructive

Question 7

What is COHERENCE?

Answer 7

Ability of two waves to interfere with each other.

Question 8

How does OCT use COHERENCE?

Answer 8

Use interference to detect change in coherence of light passing through the layers of the eye.

Question 9

What is DIFFRACTION and give an example?

Answer 9

1. Light waves bend (spread) slightly when they encounter an aperture.
2. The smaller the aperture, the greater the diffraction
3. Example: The pupil (Pupil aperture of less than 2.5 mm begins to limit acuity) and an AIRY DISC

Question 10

What is SCATTERING and give an example?

Answer 10

1. Light interaction with particles of similar wavelengths.
2. BLUE scatters more (since SHORTER wavelength=higher scattering)
3. Wider, irregular spacing or larger particles scatter all visible wavelengths
4. Example: clouds, CORNEAL EDEMA; Asteroid Hyalonosis

Question 11

What is REFLECTION and give an example?

Answer 11

1. Ex: Asteroid Hyalosis

Question 12

What is PIN HOLE Occluder and example of and how big is it?

Answer 12

1. Diffraction

2. 1.2 mm - optimal size (balances effectiveness vs diffraction -diffraction occurs when PH <1.2)

Question 13

What is the refractive index of water?

Answer 13

1.33

Question 14

What is the refractive index of Aqueous?

Answer 14

1.336

Question 15

What is the refractive index of vitreous?

Answer 15

1.34

Question 16

What is the refractive index of cornea?

Answer 16

1.376

Question 17

What is the refractive index of crystalline lens?

Answer 17

1.42

Question 18

What is critical angle and what is an example?

Answer 18

Angle at which light is bent exactly 90 away from the normal.
Example: glass/air interface = 41 degrees.

Question 19

What is total internal reflection and give examples?

Answer 19

1. Angle of incidence exceeds the critical angle.

Example: Gonioscopy, fiber optics, indirect ophthalmoscope eye pieces.

Question 20

YAG laser is a example of?

Answer 20

Photodisruption

Question 21

Excimer laser is an example of?

Answer 21

Photoablation - carbon-carbon, carbon-nitrogen bonds are directly broken and tissue is vaporized.

Question 22

Pinhole acuity is limited to what range of refraction?

Answer 22

-5 to +5

Question 23

What is TEMPORAL coherence?

Answer 23

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.

Question 24

What is the refractive index of silicone?

Answer 24

1.438

Question 25

Eximer laser in refractive surgery falls in what part of the light spectrum?

Answer 25

Ultraviolet