Perimetry Fundamentals

Question 1

Kinetic Perimetry (moving target)

Answer 1

A measure of the perimeter (outermost) area of VF within a test spot of constant luminance and size.
“Look straight ahead and let me know when you see a stimulus move into your periphery.”

Question 2

Static perimetry

Answer 2

A measure of the increment threshold luminance for a spot of constant size at different VF locations. Spot will change luminance automatically. Flashing target. Like at ECP

Must be brighter in periphery

Question 3

Normal limits of monocular VF

Answer 3

100 degrees temporal
60 degrees nasal
60 degrees superior
75 degrees inferior

Question 4

Where is blind spot located at on VF

Answer 4

Blind spot is on the same side of the VF as he eye being tested. Blind spot on right, looking at the right eye.

Question 5

How to present VF?

Answer 5

Always present visual field with RT eye on right side of diagram and left eye on left side of diagram.

Question 6

Which is larger? Binocular VF or monocular VF?

Answer 6

Monocular

Question 7

The normal VF is most sensitive to detecting a difference between the target luminance and background luminance at the fovea. Abnormal reduction in sensitivity of an area can be called a

Answer 7

Depression

Question 8

Constriction/contraction of VF

Answer 8

Means field is not as wide in the periphery in one direction

Question 9

Isopter

Answer 9

The actual perimeter of the observers VF as measured using:
a single stimulus
Specific size
Constant illuminance
Under specific viewing conditions

Perform kinetic perimetry from all different areas of peripheral field and measure where patient could first detect target.

Question 10

Isopter size normally increases with

Answer 10

Brightness or larger stimuli.

EX: Bringing a basketball into periphery vs a marble.

Question 11

How can you change the intensity when measuring Isopters?

Answer 11

In the settings, 1-4 represents 0.5 log unit change
a-e represents 0.1 log unit change.

More than 100 combinations possible. Only a few are clinically needed. Generally, want to use a smaller target to be more accurate.

Question 12

Intensity for plotting Isopters is measured in

Answer 12

Apostilbs. (Candella/ pi m^2)

Simplifies calculations involving circular stimuli.

Question 13

Islands or “Hills” of vision based on static perimetry.

What do these hills look like under photopic (white background) and scotopic (Black background) conditions?

Answer 13

Photopic: Best sensitivity at the fovea. Sensitivity declines quickly in surrounding retina. Cone shape.

Scotopic: Rods are much better at capturing light in the dark. Overall hill of vision is higher, with a crater at the fovea since no rods are present there. Looks like a square with a chunk taken out in the top center where fovea is.

Question 14

Under photopic conditions, peripheral targets require more luminance contrast between the target and background for detection than do central targets. Why?

Answer 14

Because ganglion cells in the periphery have larger receptive fields than those in central retina.
A target that fills the center of the RF for a central ganglion cell would elicit the best response. This target may not fill the center of a peripheral GC receptive field.

Question 15

Webers constant vs size

Answer 15

A large stimulus presented under photopic conditions to the fovea stimulates several ganglion cell receptive fields. Results in a flat contour.

A smaller stimulus results in a steep contour at the fovea.

Webers constant on Y, Eccentricity on X.

Question 16

A longer stimulus duration (up to critical duration) will result in (better or worse) thresholds

Answer 16

Better!

Question 17

The best stimulus duration should be ___ than saccadic eye movement latency and ___ than the critical duration for complete temporal summation.

What is usually used?

Answer 17

Shorter (S for saccadic)
and longer

200ms usually used.

Question 18

The inverted log Db (decibel) scale used to measure the sensitivity of “hill” vision relative to the brightest stimulus that the perimeter can produce.
What does 0 db mean? What about 50(max) db mean?

Answer 18

0 db means that the patient is unable to detect the brightest spot that the machine could produce.

50 means that the patient was able to detect the dummest light that the machine could produce.

Question 19

Difference between relative and absolute scotoma?

Answer 19

Relative: Pt sensitivity in that area is decreased, but still measurable.

Absolute: NLP

Question 20

Positive scotoma vs negative scotoma

Answer 20

Positive scotoma; Pt is aware in Foss of sensitivity

Negative: Pt is unaware of loss in sensitivity. EX: blind spot

Question 21

How are we entirely unaware of our blind spots existence?

Answer 21

Even monocularly, our brain fills in the blind spot in our VF with whatever colors, textures, or contours are present in the surround. This also occurs with natural and long standing blind spots/lesions.

Question 22

Visual neglect: Perceptual and motor

What are these usually related to?

Answer 22

Perceptual: Failure to attend to or represent sensory info from 1 side of the body or VF

Motor: Failure to execute movements fully towards one half of the VF.

usually related to contralateral lesions that are important for visually guided behavior.

Question 23

Visual extinction

Answer 23

Parietal lobe damage. The sensory deficit (visual neglect) only emerges when stimuli are presented simultaneously to the left and right sides.

Ex: RT parietal lobe lesion. When stimuli are presented simultaneously to the left and right sides, pt will ignore stimulus presented in the left.

Question 24

Useful VF

Answer 24

Central and peripheral vision used to multitask. Ex: Texting and driving.

Very restricted compared to normal VF.