Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Optometric theory and techniques > Lensometry, prism, and hand neutralization > Flashcards

Lensometry, prism, and hand neutralization Flashcards

1
Q

Where is the far point for a myopic eye?

A

before the cornea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where is the far point for a hyperopic eye?

A

after the retina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Primary focal point

A

object-space focus. Distance from the optical surface to the primary focal point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Primary focal point for a plus lens

A

point from which light must originate to emerge parallel from the lens. Image is at infinity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Primary focal point for a minus lens

A

Point towards which the incident light must be directed in order for the image rays to emerge parallel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

collimated

A

rays are parallel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

secondary focal point

A

image-space focus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

secondary focal point for a plus lens

A

parallel rays from a distant point object are rejoined to form an image at that point.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

secondary focal point for minus lens

A

diverging rays seem to come from, after a parallel bundle of rays are refracted by a negative lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Plus lenses

A

magnify

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

minus lenses

A

minify

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

lensometer

A

lensmeter/focimeter/vertometer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does a lensometer measure?

A

sphere, cylinder, axis, add power, prism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Down stream vergence

A

P/(1-[t/n2)P

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

lens power

A

(n’-n)/r

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Approximate power

A
  • P1+P2.
  • Matches closely with back vertex power of minus lens.
  • matches closely with thin lens
  • cannot be used for manufacturing because error in app can be significant
  • convenient/simple
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Front vertex power

A

also called the neutralizing power.
=P2/(1-[t/n2]P2) + P1
Used in hand neutralization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Back vertex Power

A

Badal
Standard spectacle lens correction
Used for specifying power of spectacle lenses
=P1/(1-[t/n2]P1) +P2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

equivalent power

A

P1 + P2 + (t/n2)P1P2

Different lenses with the same EP can provide differring corrective powers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Effective power

A

P/(1-[t/n2]P)

  • used for things at a distance, needs to be addressed when RXing CL
  • the further away, the more power is needed
21
Q

Why is effectivity important?

A

accomodative demand
CL calculations
Refractive surgery calcs

22
Q

Practice problem in this slide show

A

do it

23
Q

astigmatism

A

common vision condition that causes blurred vision. It occurs when the cornea is irregularly shaped or sometimes because the curvature of the lens in the eye

24
Q

spherecylindrical lenses

A

axes cannot exceed 180

25
Q

How does the angle increase for cyl

A

from patients left to right

26
Q

lensometry

A
  • measures back vertex power in diopters

- uses a standard lens of known power

27
Q

What is the effect of prism?

A
  • deviation of light rays towards the base of prism

- the image will appear to move towards the apex of the prism

28
Q

where does the image appear to move towards in a prism?

A

the apex

29
Q

magnification

A

m=-i/o

30
Q

Abbe number

A
  • constringence or V-number
  • transparent material’s chromatic dispersion
  • shows the variation of refractive index versus the wavelength
  • High Abbe, Low dispersion
31
Q

what can affect refractive index?

A

wavelength and temperature

32
Q

what color has the lowest index of refraction?

A

red

33
Q

what color has the highest index of refraction

A

violet

34
Q

How do you measure prism?

A

1 prism diopter creates a deviation of 1cm at 1 m

5 prism diopters creates a deviation of 5cm at 1m

35
Q

describe orientation of image in BI

A

image goes out

36
Q

describe orientation of image in BO

A

image goes in

37
Q

describe orientation of image in BU

A

image goes down

38
Q

describe orientation of BD

A

image goes up

39
Q

amount of prism

A

prism=P x d (in cm)

40
Q

prentice’s rule

A

prims=P x d (in cm)

41
Q

hand neutralization for minus lens

A

with motion
upright
minified

42
Q

hand neutralization for plus lens

A

against motion
inverted
magnified

43
Q

How do you find front vertex?

A

hand neutralization

44
Q

how do you find back vertex?

A

lensometer

45
Q

What is the back surface power of first lens equal and opposite to in thick lens?

A

the neutralizing power in the second lens

46
Q

On a thick lens, if the unknown lens is placed in back…

A

you are determining the neutralization power of the unknown lens using the back vertex power of the known lens

47
Q

in thick lens, if the known lens is placed in back, you are determining…

A

the back vertex power of the unknown lens based on the neutralization power of the front lens (which might be different than the known back vertex power

48
Q

spherocylindrical

A

turning this type of lens gives a scissors motion

Optometric theory and techniques (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions