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Ophthalmics > Absorptive Lenses > Flashcards

Absorptive Lenses Flashcards

1
Q

UVA wavelength

A

320-380 nm

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2
Q

UVB wavelength

A

290-320 nm

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3
Q

UVC wavelength

A

200-290nm

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4
Q

Visible spectrum wavelength

A

380-760nm

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5
Q

Infrared spectrum

A

760nm - 1mm

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6
Q

What 3 factors determine light transmission through a lens?

A

1)percentage of light lost by reflection-front surface
2)percentage of light lost by absorption
3)percentage of light lost by reflection-back surface

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7
Q

What is the equation to find the amount of light reflected by a lens surface? (Reflection Equation)

A

Amount of light reflected = (n’ - n)^2 (I) / (n’+n)^2

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8
Q

What is the equation to find the amount of light that is transmitted through a lens?

A

Transmission= Incident Light - Absorption - Reflection

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9
Q

What does Lambert’s law of absorption say? What factor represents this?

A

For an absorptive material, layers of equal thickness absorb equal quantities (percentages) of light regardless of the intensity of the light.

Transmittance factor (q)

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10
Q

How do you find Transmission when incident light and transmittance factor is given?

A

Transmission= incident light (%) x transmittance factor (q) (number of thicknesses)

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11
Q

How do you find ultimate transmission?

A

individual transmissions multiplied by the others if it passes through more than one lens.

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12
Q

What is opacity? Equation?

A

Reciprocal of transmission

Opacity= 1/Transmission

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13
Q

How do you find ultimate opacity?

A

Opacity multiplied by other opacities.

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14
Q

How do you find optical density?

A

Optical density= -log(transmission)

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15
Q

How much transmission is normal for plastic sunglass lenses?

A

15-30%

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16
Q

How much transmission is normal for general-purpose lenses?

A

8%-40%

17
Q

What do photochromic glass lenses contain that allows them to change color?

A

silver halide crystals.
Turns into silver and halogen atoms with UV.

18
Q

What do corning photochromic filter (CPF) lenses look like? What are they used for?

A

Appear orangish.
They filter out the shorter wavelengths like blue in order to relieve glare for patients with severe light sensitivity.

19
Q

What molecule is found in plastic transition lenses that allow them to change color?

A

Spiro-Oxazine molecule

20
Q

What is meant by an imbibed photochromic lens (transition lens)?

A

The lens darkens evenly across the lens regardless of prescription. The transition layer is on the outside surface of the lens only.

21
Q

What is meant by an In-mass photochromic lens (transition lens)?

A

The transition molecules are found throughout the whole lens. They darken up to 50% in the car. Scratches do not affect performance. The transition molecules never wear out.

22
Q

What transition lenses do not change behind a car windshield?

A

Transition Signature Lenses GEN 8

23
Q

What transition lenses DO change and have moderate activation behind a car windshield?

A

Transition XTRActive Lenses New Generation
Transition Drivewear Lenses

24
Q

What is a concern with transition motorcycle visors?

A

Whether or not they can change quick enough if they were to go under a tunnel.

25
Q

What are the 4 types of glare?

A

Distracting Glare
Discomfort Glare
Disability Glare
Reflected Glare

26
Q

What type of glare is caused by lens reflections?

A

Distracting glare

27
Q

What type of glare is caused by stray light that causes visual discomfort but does not interfere with resolution?

A

Discomfort glare

28
Q

What kind of glare makes objects appear like they have lower contrast than they would without the glare. It increases the brightness of the background and lowers the brightness of the nearby object?

A

Disability glare

29
Q

What kind of glare is caused by reflected light sources and known as ‘blinding glare”?

A

Reflected glare

30
Q

Axis that blocks all polarized light incident at that axis

A

Absorption axis

31
Q

Axis that transmits all polarized light incident at that axis

A

Transmission axis

32
Q

What direction of light is mostly reflected off a horizontal surface like a body of water?

A

Horizontal light waves

33
Q

What materials polarize light the best?

A

Nonconducters, dielectrics, glass, pavement, sand, snow

34
Q

The angle where all the light reflected off a dielectric is completely polarized

A

Brewster/s Angle

35
Q

How do you find Brewster’s Angle?

A

Tan(i) = n’

i= angle of incidence
n’= index of the medium

36
Q

How to solve for i in brewster’s angle equation

A

i= tan^-1 (n’)

37
Q

What does malus’s law determine? What is the equation?

A

Determines the intensity of light that passes through two perfect polarizers.

Io = I cos2 θ

I= initial intensity
Io= intensity after two polarizers
θ= angle betweeen transmission axis of the polarizers

38
Q

What percent of transmission must aviation glasses have?

A

At least 15% of transmission

Ophthalmics (7 decks)

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