Brainscape's Knowledge GenomeTM

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


See full index

Optics Block 8 > Subjective And Objective Refraction > Flashcards

Subjective And Objective Refraction Flashcards

1
Q

The patient makes a judgment of the correct focus

A

Subjective techniques

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

An instrument makes a judgement of the correct focus

A

Objective techniques

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

The half width of the diffraction limited PSF is 3.23. If the spherical aberration of 0.5 microns is added to this PSF, what would happen to the PSF

A

Increase

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

Calculate the strehl ratio, if the maximum light level of the diffraction limited PSF is 65 lumens, and the maximum light level of the aberrated PSF is 40 lumens

A

40.65=0.6

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

What gets transferred in a grating

A

Contrast (modulation)

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

How do you measure MTF

A

A’/A

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

Which of the following aberrations decrease in amplitude and experience transverse shift

A

Coma

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

The spatial freqqucny at which MTF goes to 0 is called as

A

Resolution limit

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

Devices that control the focus of the retinal image for the purpose of measuring the power of the eye are called

A

Optometers

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

What is the root name for the profession of optometry

A

Optometer

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

When are optometers subjective

A

If the patient judges the clarity of the retinal image

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

When is an optometer objective

A

If a machine or the examiner does it

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

What does a simple optometer consist of

A

Moveable target and a fixed positive power lens placed at its focal distance away from the eye

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

Advantages of simple optometer

A

Allows both positive and negative vergences

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

Disadvantages of simple optometer

A

Target vergence and angular size varies inversely with the target distance

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

What are the 3 draw backs of not using instruments in optometry

A
  • increases target vergence
  • object looks magnified (increase in angular size)
  • no 0 or + vergence, only negative vergence
17
Q

How did badal optometer overcame the challenges of simple optometer

A

Moveable auxiliary lens

18
Q

Badal principle

A
  1. Auxiliary lens (minus) placed in between the target and the badal lens
  2. Eye is placed at the back focal point of the badal lens (plus)
  3. Then the target vergence and angular size of the perceived object remains independent of the target distance allowing for both positive and negative vergence
19
Q

Four advantages of the badal optometers

A
  • linear power scale
  • uniform sensitivity
  • irradiance of the eye
  • constant focus: (accommodation)
20
Q

How is power related to the actual target distance

A

Power is linearly related to the actual target distance

-power increases as target distance increases

21
Q

What happens to the angular size with badal optometer

A

Remains unchanged

22
Q

Irradiance of the eye in the badal optometer

A

The irradiance of the source at the eye is constant for any distance of the target

23
Q

Focus and the badal optometer

A 
Constant focus (accommodation)
-the apparent position of the eye will be at optical infinity for all position of the target
24
Q

Laser speckle optometer

A

Laser light reflected from a matte surface or transmitted through a diffuser causes an interference pattern at the retina that was perceived by an observer as a speckle pattern

25
Q

Laser speckle optometer for myopic eye

A

The speckle pattern appears to move in the same direction as the moving screen

26
Q

Laser speckle optometer for a hyperopic eye

A

The speckle pattern appears to move in the opposite direction of motion is observed

27
Q

How does the emmetropic eye see the laser speckle optometer

A

As a “boiling” pattern

28
Q

Newtons relationship for the speckle laser optometer

A

xx’=ff’

29
Q

What is the vergence for the speckle laser optometer

A

V=1/x’=x/ff’

30
Q

Application of the speckle laser optometer

A
  • measurement of subjective refractive error in dim conditions
  • investigation of aspects of accommodation, like determining the resting place of accommodation
31
Q

Eye focuses when there is nothing to focus on

A

Resting place of accommodation

Optics Block 8 (9 decks)

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