Optical intruments 2

Question 1

What is visual field?

Answer 1

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

Question 2

How do you measure visual field?

Answer 2

Perimetry

Question 3

What is the normal monocular visual field?

Answer 3

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

Question 4

What is the overall visual field determined on?

Answer 4

by facial contours

Question 5

What does temporally mean?

Answer 5

extends out towards ear

Question 6

What does nasally mean?

Answer 6

towards nose

Question 7

What will the extent of the binocular visual field be?

Answer 7

200deg
60deg up
75deg down

Question 8

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

Answer 8

d

Question 9

What does every point in the retina correspond to?

Answer 9

a certain direction in the visual field.

Question 10

What visual field does the nasal retinal area correspond to?

Answer 10

temporal (and vice versa)

Question 11

What visual field does the superior retinal area correspond to?

Answer 11

inferior (and vice versa)

Question 12

What visual field does the temporal retinal area correspond to?

Answer 12

nasal

Question 13

What visual field does the inferior retinal area correspond to?

Answer 13

superior

Question 14

Where does the blind spot occur?

Answer 14

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

Question 15

Why does a blind spot form?

Answer 15

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

Question 16

What is the location of a blind spot?

Answer 16

centre situated approx 15degrees temporally

1.5degrees below horizontal meridian

Question 17

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

Answer 17

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.

Question 18

Where is the blind spot located on the right eye?

Answer 18

on the right

15degrees temorally and 1.5degrees below horizontal meridian

Question 19

What is the 2 types of perimetry?

Answer 19

kinetic

static

Question 20

What is kinetic perimetry?

Answer 20

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

Question 21

What is static perimetry?

Answer 21

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

Question 22

What is the gross perimetry?

Answer 22

it follows facial contours ( judging their eyelids etc)

Question 23

What is a confrontation?

Answer 23

comparing patient visual field with the examiner.

Question 24

Where is static perimetry measured at?

Answer 24

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

Question 25

What does every point in the retina have?

Answer 25

a certain threshold sensitivity

Question 26

How is the visual field recorded in static perimetry?

Answer 26

in decibels or log units

Question 27

What is the maximum stimulus luminance of a perimeter?

Answer 27

0dB (the brightest light)

Question 28

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

Answer 28

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

Question 29

Where do you do static perimetry?

Answer 29

in pre-screening

Question 30

What is a suprathreshold screening?

Answer 30

can see stimuli above a certain threshold

Question 31

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

Answer 31

a scotoma

Question 32

What is scotoma?

Answer 32

a partial loss of vision

Question 33

What is full threshold?

Answer 33

measures the precise threshold sensitivity by varying stimuli intensities

Question 34

What is the difference between suprathreshold and full?

Answer 34

faster than full threshold.

Question 35

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

Answer 35

centre of fovea

Question 36

What is the advantages of suprathreshold screening?

Answer 36

rapid examination of visual field

Question 37

What are the disadvantages of suprathreshold screening?

Answer 37

not as accurate as full threshold perimetry | can miss defects if the threshold is incorrectly estimated

Question 38

What are the advantages of full threshold?

Answer 38

more accurate than suprathreshold perimetry reliability data given diagnostic info

Question 39

What are the disadvantages of full threshold?

Answer 39

slow

Question 40

How is the suprathreshold set up?

Answer 40

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

Question 41

What is suprathreshold- two zone?

Answer 41

Two zone- which is marked as seen or not seen (the light) | Points missed out twice are marked as blank on the printout

Question 42

Why is two zone not accurate?

Answer 42

as it doesnt tell what level the light is seen. | not good to determine a defect.

Question 43

What is suprathreshold- with quantification?

Answer 43

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

Question 44

What are the different visual fields test?

Answer 44

Henson Visual field analyser- multiple and single stim | Humphrey visual field analyser

Question 45

What does multiple stimulus mean?

Answer 45

number of lights shown at the same time

Question 46

What does single stimulus mean?

Answer 46

One light shown

Question 47

What are the tests for humphrey machine?

Answer 47

Binocular vision | central vision

Question 48

How does the full threshold work?

Answer 48

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

Question 49

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

Answer 49

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

Question 50

What are the new generation algorithms?

Answer 50

- 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.

Question 51

Summary of suprathreshold single stimulus (Henson) test:

Answer 51

- 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)

Question 52

Summary suprathreshold multiple stimulus (Henson):

Answer 52

- 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.

Question 53

Does a patient need to wear their glasses to do their test? | What do they need to make sure?

Answer 53

Yes, their reading glasses if they are presbyopic. | Need to make sure the glasses frame does not obstruct the test.

Question 54

Test: estermann visual field test (Humphrey) :

Answer 54

- 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.

Question 55

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

Answer 55

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.

Question 56

When do we do a visual field test?

Answer 56

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