Midterm 2: Perimetry Flashcards
Region of space where one eye can see but the other can not.
Monocular temporal crescents.
Where FOV does not overlap with both eyes
What did Traquair say about visual field?
- compared it to an island, surrounded by sea of blindness.
- as you get further away from fovea, your sensitivity to seeing the target drops and can’t see it as well.
About how many degrees from the central FOV would you find the blind spot?
about 15-18 degrees
Where is the visual field most sensitive to detecting difference in target luminance and background luminance?
At the fovea
What do you call an abnormal reduction in sensitivity of an area the visual field? Where do people always have a depression?
A depression. Optic nerve because no photoreceptors
What is isopter?
During kinetic perimetry, the isopter is the measured values of their field of view measured by a constant stimulus size and constant luminance.
If you increase the stimulus size or luminance, would this increase or decrease isopter?
Increase
Kinetic perimetry stimulus
Constant luminance and constant stimulus size. Changing the location of the stimulus.
Static perimetry stimulus characteristics
Stimulus is changing luminance, remaining same size at different locations. Wants to find the increment detection threshold for certain parts of the visual field.
On a right eye, would the blind spot be left or right of the central vision?
Right
Binocular visual field in degrees. Horizontal and vertical
Horizontal: 120 degrees
Vertical: 135 degrees
Total visual field in degrees. Horizontal and vertical
Horizontal: 200 degrees
Vertical: 135 degrees
What is an apostilb?
Unit of intensity for Goldmann kinetic perimetry stimuli.
units are candelas/ pi x meter squared
-are in log unit steps
-values 1-4 and 0.5 log steps
Are large or smaller stimulus targets better for detecting the isopter edges?
Smaller targets are better
Is a V4e stimulus large and bright or dim and small?
Largest and brightest possible
What do the Roman numerals mean for the stimulus? What does the “1e, 2e, 3e” mean?
Roman numerals refer to size. Higher Roman numeral = larger stimulus
“1e, 2e…” refers to brightness. Larger number = more bright
Describe x and y axis of the 2-D perimetry hill of vision graph on kinetic perimetry
Y-axis: sensitivity
X-axis: retinal postion
Difference of hill of vision between scotopic and photopic
scotopic graph is much larger but should have a depression in the very center since we have cones in the fovea and they aren’t good in dark.
What background luminance do most automated perimeters use?
10 cd/m^2 or 31.4 asb which is low photopic range
What kind of contour does a large stimulus have on a graph?
Flat. Meaning it stimulates a lot of receptive fields
What kind of contour does a smaller stimulus have?
Steeper. It tests fewer receptive fields so it is more sensitive.
Two factors of stimulus duration of static perimetry
Temporal summation:
- Photopic- only need 10-50 msec
- Scotopic- 100 msec
Saccadic eye movement latency:
-Approx 250 msec. If it stays on at least 250 msec, patient may saccade toward the stimulus.
best duration for stimulus In static perimetry?
longer that critical duration but shorter than saccadic eye movement latency.
-around 200 msec
Does a high number (5) on log asb indicate good or bad sensitivity?
Good
What does it mean if a patient has a sensitivity of 0 decibels?
They were not able to detect brightest stimulus given to them. Does not mean they are blind
What do we define the scotoma by?
By its depth. Relative vs. Absolute scotoma
What is relative scotoma
over threshold but measurable and doesn’t mean total loss of vision
Absolute scotoma
no light perception
Positive scotoma
patient is aware of loss in sensitivity
negative scotoma
patient is unaware of loss of sensitivity
What kind of scotoma is the optic nerve?
negative scotoma. We do not perceive vision is gone due to filling in.
Perceptual visual neglect
failure to attend to sensory information on one side of the body
Motor visual neglect
failure to execute movements to one side of the visual field.
Why does a person usually exhibit visual neglect?
Usually a contralateral lesion in dorsal extra-striate visual pathway
Visual extinction
usually occurs with parietal lobe damage
the visual neglect only emerges when stimuli are presented simultaneously
If pt has right parietal lobe lesion, where will patient ignore stimulus?
patient will ignore left visual field when stimulus is present in both left and right visual fields.
How to perform useful visual field
Having patient focus on object at fixation and present another stimulus in periphery.
Useful visual field on elderly
sometimes restricted even though traditional visual field may be normal
What is flicker defined form perimetry useful for?
Detecting visual field loss in early glaucoma patients
