Lec.5: Visual Fields

Question 1

in VF perimetry where does the blind spot sit?

Answer 1

15 degrees temporally

Question 2

(T/F) nerve fibers from the superior retina cross over to the inferior retina and vice versa?

Answer 2

False (nerves respect the midline

Question 3

what parameters detect a weak stimulus (dim light)?

Answer 3

low threshold and high sensitivity

Question 4

what parameters detect a strong stimulus (bright light)?

Answer 4

high threshold and low sensitivity

Question 5

in HFA II what is the distance between the eye and field of view?

Answer 5

30 cms

Question 6

which phenomenon states that moving targets are more visible than non-moving targets?

Answer 6

Riddoch phenomenon

Question 7

what happens to intensity as the decibel value increases?

Answer 7

higher the decibel value (40 dB) the lower the intensity of the stimulus

Question 8

what represents the intensity that is just marginally visible (patient will perceive light 50% of the time)?

Answer 8

threshold

Question 9

how is the isopter determined?

Answer 9

moving a stimuli from a region in the periphery where it is infra threshold to a region where it is supra threshold.

Question 10

what are some reasons for using brighter light in VF testing?

Answer 10

testing peripheral retina, or testing damaged retinal tissue

Question 11

what effect occurs when one fixates at a particular point and after about 20 secs a stimulus away from the fixation point (periphery) starts to fade and disappear?

Answer 11

troxlers effect

Question 12

what is the gold standard in VF test?

Answer 12

24-2 SITA standard

Question 13

in regards to reaction time, how does a SITA VF differ from older strategies?

Answer 13

speeds up test for fast responder and slows it down if responses are slower

Question 14

what are the 3 types of catch trials detected by a VF machine?

Answer 14

false positive, false negative and fixation loss

Question 15

what percentage of stimulus is presented in the Heijl-Krakau blind spot method?

Answer 15

5% of stimulus presented are used to check fixation

Question 16

and what is the average size of that blindspot?

Answer 16

5 degrees wide by 7 degrees tall

Question 17

what is it called when a patient responds when no stimulus is present?

Answer 17

false positive

Question 18

what is it called when patients fails to recognize proportion of visible stimuli?

Answer 18

false negative

Question 19

what the are acceptable SITA rates?

Question 20

(T/F) Hippus affects VF results?

Answer 20

false

Question 21

what size pupil needs to be dilated for a VF test?

Question 22

do you dilate patients with catarcts prior to running a VF?

Answer 22

yes

Question 23

what must always be entered before performing a VF test?

Answer 23

patient age and refractive error

Question 24

what are the type of defects that you can quickly identify in a grey scale image?

Answer 24

central, paracentral, nasal defects and blind spot

Question 25

are peripheral points of interest in a 30-2?

Answer 25

no, but they are in 24-2

Question 26

what raw data values would you expect to see centrally? and Peripherally?

Answer 26

``` centrally= threshold of lower 30's dB peripherally= threshold of upper 20's dB ```

Question 27

when examining the total deviation plot, what values can be viewed suspiciously?

Question 28

what does a p-value of 0.5% mean?

Answer 28

chance that they are normal is less than 0.5%

Question 29

how does fixation differ in octopus than in humphrey?

Answer 29

in octopus the machine detects a loss of fixation and stops projecting light (automated eye tracking)

Question 30

how do the humphrey and octopus machines indicate an area where light is not detected?

Answer 30

``` humprey= assigns a zero value octopus= assigns a black square ```

Question 31

how are defects represented in a humphrey and in an octopus reading?

Answer 31

``` humphrey= negative value octopus= will give you a positive number ```

Question 32

what global indices in HFA and octopus mean the same thing?

Answer 32

mean deviation= mean defect | pattern standard deviation= loss of variance

Question 33

when examining the pattern deviation what are the p-value criteria for a cluster of 3 or more points?

Answer 33

all must be depressed at a p

Question 34

can the 2-3 cluster points be in opposing hemifields?

Answer 34

NO, they must all be in the same hemifield

Question 35

when staging glaucoma based on a MD score: better than -6 dB

Answer 35

mild

Question 36

when staging glaucoma based on a MD score: worse than -6 dB but better than -12 dB

Answer 36

moderate

Question 37

when staging glaucoma based on a MD score: worse than -12 dB

Answer 37

severe

Question 38

when staging glaucoma based on the Brusini graph, what is plotted along the y-axis and what is plotted along the x-axis?

Answer 38

y-axis is PSD | x-axis is MD

Question 39

what classifications of defects does the Brusini graph allow you to identify?

Answer 39

localized defect, mixed defect or generalized defect

Question 40

in early glaucoma, does the VF defect tend to remain steady?

Answer 40

no it tends to fluctuate

Question 41

what represents a worse mean defect result in HFA?

Answer 41

negative number

Question 42

what correlates with a worse mean defect result in octopus?

Answer 42

larger (positive) number

Question 43

what may lead to errors during a VF test?

Answer 43

miosis, lens opacities, uncorrected refractive error, ptosis, inadequate adaptation, lenses too far way from the eye

Question 44

what is percentage of M cells?

Answer 44

10%

Question 45

what is the percentage of P cells?

Answer 45

80%

Question 46

what is the percentage of K cells?

Answer 46

9%

Question 47

what are the names of cells that make the magno system?

Answer 47

Parasol, Palpha, M or MC, phasic or broad band

Question 48

what are the names of cells that make the parvo system?

Answer 48

Midget, Pbeta, P or PC, tonic or color opponent

Question 49

what FDT (frequency doubling technology) screening test allows you to test functioning of M-cells?

Answer 49

low spatial frequency sinusoidal grating (greater spacing between the bars)

Question 50

what are the advantages of N-30-5 screening test?

Answer 50

only take 1 min 15 secs and has a 5% chance that a normal person has an error