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clinical skills > Optical intruments 2 > Flashcards

Optical intruments 2 Flashcards

1
Q

What is visual field?

A

the area in space within which the eye can percieve a visual stimulus without altering its position of gaze.

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2
Q

How do you measure visual field?

A

Perimetry

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3
Q

What is the normal monocular visual field?

A

100degs temporally (out towards ear)
60degs nasally
60degs up
75degs down

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4
Q

What is the overall visual field determined on?

A

by facial contours

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5
Q

What does temporally mean?

A

extends out towards ear

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6
Q

What does nasally mean?

A

towards nose

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7
Q

What will the extent of the binocular visual field be?

A

200deg
60deg up
75deg down

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8
Q

What’s the difference between central and peripheral visual fields?

A

d

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9
Q

What does every point in the retina correspond to?

A

a certain direction in the visual field.

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10
Q

What visual field does the nasal retinal area correspond to?

A

temporal (and vice versa)

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11
Q

What visual field does the superior retinal area correspond to?

A

inferior (and vice versa)

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12
Q

What visual field does the temporal retinal area correspond to?

A

nasal

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13
Q

What visual field does the inferior retinal area correspond to?

A

superior

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14
Q

Where does the blind spot occur?

A

in area of visual field which corresponds to projection of optic disc ( also known as optic nerve head)

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15
Q

Why does a blind spot form?

A

there is no photoreceptors (rods and cones) in optic disk

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16
Q

What is the location of a blind spot?

A

centre situated approx 15degrees temporally

1.5degrees below horizontal meridian

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17
Q

Why is it important to know where the blind spot when measuring visual fields?

A

ensure the patient is fixated
so you know where the normal blind spot to check if there are any other problems as if a patient has many blind spots it means that the retina is not stimulated by light in those areas so if you had a retinal defect the visual field would be reduced.

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18
Q

Where is the blind spot located on the right eye?

A

on the right

15degrees temorally and 1.5degrees below horizontal meridian

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19
Q

What is the 2 types of perimetry?

A

kinetic

static

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20
Q

What is kinetic perimetry?

A

moving a target to asses the extent of the visual field and stimulus is a fixed size and moving it from a non-seeing to seeing until is detected by the patient
via e.g gross perimetry and goldmann perimeter

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21
Q

What is static perimetry?

A

targets presented diff points in the visual fields and determine the sensitivity

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22
Q

What is the gross perimetry?

A

it follows facial contours ( judging their eyelids etc)

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23
Q

What is a confrontation?

A

comparing patient visual field with the examiner.

24
Q

Where is static perimetry measured at?

A

the visual field is probed at specific static points and threshold sensitivity is recorded

25
Q

What does every point in the retina have?

A

a certain threshold sensitivity

26
Q

How is the visual field recorded in static perimetry?

A

in decibels or log units

27
Q

What is the maximum stimulus luminance of a perimeter?

A

0dB (the brightest light)

28
Q

What does it mean if the number read of the perimeter is high?

A

the higher the number, the higher the threshold sensitivity and the dimmer the light presenteD

29
Q

Where do you do static perimetry?

A

in pre-screening

30
Q

What is a suprathreshold screening?

A

can see stimuli above a certain threshold

31
Q

What does it mean when a stimulus can not be seen and is not a blind spot?

A

a scotoma

32
Q

What is scotoma?

A

a partial loss of vision

33
Q

What is full threshold?

A

measures the precise threshold sensitivity by varying stimuli intensities

34
Q

What is the difference between suprathreshold and full?

A

faster than full threshold.

35
Q

Where is the peak sensitivity of the visual field / corresponds to?

A

centre of fovea

36
Q

What is the advantages of suprathreshold screening?

A

rapid examination of visual field

37
Q

What are the disadvantages of suprathreshold screening?

A

not as accurate as full threshold perimetry

can miss defects if the threshold is incorrectly estimated

38
Q

What are the advantages of full threshold?

A

more accurate than suprathreshold perimetry
reliability data given
diagnostic info

39
Q

What are the disadvantages of full threshold?

A

slow

40
Q

How is the suprathreshold set up?

A
  1. Age-related strategy- where stimuli set by the instrument at a certain number of decibels higher than age-matched normal (light is higher depending on age)
  2. threshold related strategy- determine the threshold for 4 points within the visual field and then set to next decibel etc
41
Q

What is suprathreshold- two zone?

A

Two zone- which is marked as seen or not seen (the light)

Points missed out twice are marked as blank on the printout

42
Q

Why is two zone not accurate?

A

as it doesnt tell what level the light is seen.

not good to determine a defect.

43
Q

What is suprathreshold- with quantification?

A

If any suprahreshold stimuli are missed, the depth of the scotoma is assessed by establishing the threshold

44
Q

What are the different visual fields test?

A

Henson Visual field analyser- multiple and single stim

Humphrey visual field analyser

45
Q

What does multiple stimulus mean?

A

number of lights shown at the same time

46
Q

What does single stimulus mean?

A

One light shown

47
Q

What are the tests for humphrey machine?

A

Binocular vision

central vision

48
Q

How does the full threshold work?

A

Algorithm- staircase procedure- estimate threshold from ,measuring from a bright light then goes dimmer until the light cannot be seen.

49
Q

What is important to take for the full threshold test on machine?

A

the patients DOB- being used to set the machine, o it runs appropriately.

50
Q

What are the new generation algorithms?

A
  • To make it test faster
  • SITA standard- 50% faster than standard full theshold algorithm
  • SITA fast- 75% faster than standard full threshold algorithim BUT accuracy not as good as standard full threshold algorithm.
51
Q

Summary of suprathreshold single stimulus (Henson) test:

A
  • Fully automatic- no perimetrist required other than patient set-up and instructions
  • -Stimuli presented one at a time- 5dB above a measurement of the patients threshold
  • If missed on both occasions, the stimulus is presented at 8dB then 12dB above the threshold estimate
  • A grey scale indicates the depth of defect- if its darker the light (12dB, the more the defect etc)
52
Q

Summary suprathreshold multiple stimulus (Henson):

A
  • Present 4 lights
  • Patient is asked to report how many dots they saw and where they saw them
  • If any are not seen, position of the unseen stimulus is deduced and recorded.
53
Q

Does a patient need to wear their glasses to do their test?

What do they need to make sure?

A

Yes, their reading glasses if they are presbyopic.

Need to make sure the glasses frame does not obstruct the test.

54
Q

Test: estermann visual field test (Humphrey) :

A
  • Binocular field test - when you test both eyes
  • used for whether you are fit to drive
  • If Rx is needed to test then can use however if not required to function daily then it is not needed.
55
Q

Why is visual field test done one eye at a time?

A

there is an overlap of to fields and could compensate one eye for the other therefore needs to be done separately to test their individual visual test.

56
Q

When do we do a visual field test?

A

Symptoms e.g headaches
family history of glaucoma
IF patient has other signs of glaucoma( high IOP of suspicious optic disk)

clinical skills (13 decks)

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