Brainscape's Knowledge GenomeTM

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


See full index

My Own Deck > Visual Impairment 3- Near LVAs > Flashcards

Visual Impairment 3- Near LVAs Flashcards

1
Q

Where should an object be placed for parallel lights to emerge?

A

Anterior focal length of lens

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

What is the definition of a magnifier?

A

A plus lns allowing px to obtain increased retinal image size by holding objects closer to eye without extra demands on accommodation

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

How would a hand held mag be calculated?

A

Mag= Feq/4

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

What happens if the is not at anterior focal point?

A

Distance closer= not parallel, need reading add

Dist further= rays converging, image blurred

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

Why does dist between object and mag matter?

A

If there’s no dist= magnification is minimum

Dist increases= magnification increases

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

Why does dist between mag and pxs eye matter?

A

Effects the FOV

Relative distance mag needs to decrease as mag and eye dist increases , otherwise no effect on mag

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

How can we maximise the FOV and factors would reduce the FOV?

A

Increase FOV= Large diameter

Decrease FOV= aberrations and high powers

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

What type of lens may give a increase d field of view with minimal peripheral aberrations?

A

Aspheric lenses

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

Whar is the linear field calculation?

A

FOV= D/ d (dist b/w mag and cornea) x Feq

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

How is FOV increased in a hand held mag?

A

Move closer to lens

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

What image is created at the focal point?

A

Virtual imagev

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

What is required to help magnify an image if the object is closer than focal length?

A

Near add

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

When is illumination added to a mag?

A

If the power increases= the lens diameter decreases= the focal length decreases—– illumination added

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

How is a clear image produced in a stand magnifier news why?

A

The focal length is less than the object dist to len

Better quality image and less aberrations

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

What are the 2 components to a stand magnifier?

A

Magnifier

Reading add lens

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

What is the calculation to the 2 component system?

A

Feq= FM + FA - zFM . FA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the advantages of using a stand magnifier?

A

Accurate WD
Hands free
Internal illumination
Prolog reading

18
Q

What are the disadvantages to a stand magnifier?

A

Special reading specs required
Prevents access
Flat surface
More bulky

19
Q

When will the FOV be effected?

A

FOV will reduce as px moves AWAY from the lens

20
Q

What mag calculation is used in a stand magnifier?

A

Mag= Fequiv/4

21
Q

What ways can the mag be increased in a stand mag?

A

Increase reading add

Decrease separation between Reading add and magn

22
Q

What is the starting point reading add for a spectacle microscope to become considered an LVA and why?

A

+4.00

Why?… standard add as 1/4= 25cm

23
Q

What are the different types of spectacle magnifier?

A 
SV readers
Hyperoculars (12x)
Prismatic half eyes (+12.00D)
Bifocal units 
Clip to lenses (4x)
Head band magnifier (3x)
24
Q

What is the mag calculation used for a spectacle mag?

A

Mag= Fnew/4

25
Q

What are the advantages of a spectacle microscope?

A

Hands free
FOV max as lens close to eye
Similar to conventional specs

26
Q

What are the disadvantages of spectacle microscope?

A 
Reducing WD- writing/sewing 
Postural discomfort 
Illumination difficult 
Convergence demands
More head movement
27
Q

What 3 categories are spectacle mags subdivided into?

A

High read additions
Simple spec mag
Compound spec mag

28
Q

What powers are typically found in high reading adds specs?

A

> +3.00-

29
Q

What mags are typically seen in a simple spec mag?

A

2x- 10x

30
Q

When would a compound spectacle magnifier be useful?

A

When >10x mag required

31
Q

What does a compound spec look like?

A

2 lenses cemented together

Can be mistaken for telescope

32
Q

What is the problem with binocular spec magnifiers?

A

Close WD demand too much convergence

33
Q

If the convergence demand is too much, what rule of thumb is used?

A

Every 1D in reading add= 1 prismD added to each eye

34
Q

At what power and mag does it become difficult to achieve good BV?

A

> +8.00 (2x)

35
Q

What happens to one of the lenses in spec mag if only one lens out of the 2 is being used?

A

A balance, frosted, chavasse or semi opaque tape is used over the lens

36
Q

Which way does a bar magnifier magnify an image?

A

Vz not hz

37
Q

Which way does a flat field magnifier magnify an image?

A

All meridians

38
Q

What are the advantages of a bar/flat field magnifier

A

Self support
Inconspicuous
Light gathering properties
Binocular viewing and normal WD

39
Q

What are the disadvantages of a bar/flat field magnifier

A

No access underneath

Flat surface

40
Q

What do manufacturers give magnification based on?

A

F/4+1

41
Q

What are the advantages of a hand magnifier?

A 
Discrete 
Light
Easy to use 
Inexpensive
Convenience 
Portable and compact 
Used c dist rx
Internal illumination
42
Q

What are the disadvantages of a hand magnifier?

A 
Handling- occupy a hand and steady hand required 
Restrictive field of view 
Can case shadows
Become tired 
Shorter/spotting tasks

My Own Deck (18 decks)

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