Lec.5: Visual Fields Flashcards
in VF perimetry where does the blind spot sit?
15 degrees temporally
(T/F) nerve fibers from the superior retina cross over to the inferior retina and vice versa?
False (nerves respect the midline
what parameters detect a weak stimulus (dim light)?
low threshold and high sensitivity
what parameters detect a strong stimulus (bright light)?
high threshold and low sensitivity
in HFA II what is the distance between the eye and field of view?
30 cms
which phenomenon states that moving targets are more visible than non-moving targets?
Riddoch phenomenon
what happens to intensity as the decibel value increases?
higher the decibel value (40 dB) the lower the intensity of the stimulus
what represents the intensity that is just marginally visible (patient will perceive light 50% of the time)?
threshold
how is the isopter determined?
moving a stimuli from a region in the periphery where it is infra threshold to a region where it is supra threshold.
what are some reasons for using brighter light in VF testing?
testing peripheral retina, or testing damaged retinal tissue
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?
troxlers effect
what is the gold standard in VF test?
24-2 SITA standard
in regards to reaction time, how does a SITA VF differ from older strategies?
speeds up test for fast responder and slows it down if responses are slower
what are the 3 types of catch trials detected by a VF machine?
false positive, false negative and fixation loss
what percentage of stimulus is presented in the Heijl-Krakau blind spot method?
5% of stimulus presented are used to check fixation
and what is the average size of that blindspot?
5 degrees wide by 7 degrees tall
what is it called when a patient responds when no stimulus is present?
false positive
what is it called when patients fails to recognize proportion of visible stimuli?
false negative
what the are acceptable SITA rates?
(T/F) Hippus affects VF results?
false
what size pupil needs to be dilated for a VF test?
do you dilate patients with catarcts prior to running a VF?
yes
what must always be entered before performing a VF test?
patient age and refractive error
what are the type of defects that you can quickly identify in a grey scale image?
central, paracentral, nasal defects and blind spot
are peripheral points of interest in a 30-2?
no, but they are in 24-2
what raw data values would you expect to see centrally? and Peripherally?
centrally= threshold of lower 30's dB peripherally= threshold of upper 20's dB
when examining the total deviation plot, what values can be viewed suspiciously?
what does a p-value of 0.5% mean?
chance that they are normal is less than 0.5%
how does fixation differ in octopus than in humphrey?
in octopus the machine detects a loss of fixation and stops projecting light (automated eye tracking)
how do the humphrey and octopus machines indicate an area where light is not detected?
humprey= assigns a zero value octopus= assigns a black square
how are defects represented in a humphrey and in an octopus reading?
humphrey= negative value octopus= will give you a positive number
what global indices in HFA and octopus mean the same thing?
mean deviation= mean defect
pattern standard deviation= loss of variance
when examining the pattern deviation what are the p-value criteria for a cluster of 3 or more points?
all must be depressed at a p
can the 2-3 cluster points be in opposing hemifields?
NO, they must all be in the same hemifield
when staging glaucoma based on a MD score: better than -6 dB
mild
when staging glaucoma based on a MD score: worse than -6 dB but better than -12 dB
moderate
when staging glaucoma based on a MD score: worse than -12 dB
severe
when staging glaucoma based on the Brusini graph, what is plotted along the y-axis and what is plotted along the x-axis?
y-axis is PSD
x-axis is MD
what classifications of defects does the Brusini graph allow you to identify?
localized defect, mixed defect or generalized defect
in early glaucoma, does the VF defect tend to remain steady?
no it tends to fluctuate
what represents a worse mean defect result in HFA?
negative number
what correlates with a worse mean defect result in octopus?
larger (positive) number
what may lead to errors during a VF test?
miosis, lens opacities, uncorrected refractive error, ptosis, inadequate adaptation, lenses too far way from the eye
what is percentage of M cells?
10%
what is the percentage of P cells?
80%
what is the percentage of K cells?
9%
what are the names of cells that make the magno system?
Parasol, Palpha, M or MC, phasic or broad band
what are the names of cells that make the parvo system?
Midget, Pbeta, P or PC, tonic or color opponent
what FDT (frequency doubling technology) screening test allows you to test functioning of M-cells?
low spatial frequency sinusoidal grating (greater spacing between the bars)
what are the advantages of N-30-5 screening test?
only take 1 min 15 secs and has a 5% chance that a normal person has an error
