Confrontational Visual Fields Flashcards
Define the visual field. What is the best way to test this? What part of the visual pathway does it test?
The total area in which objects can be seen in the side (peripheral) vision as you fixate on a central point
Easier and better to test health by testing function (VF) rather than appearance (BIO)
Visual field tests the entire visual pathway instead of just testing the superficial layer
What is the extent of the VF?
60 superiorly and nasally
70 to 75 inferiorly
90-100 temporally
Binocularly extends 180 side to side
Area of vision common to both eyes extends 60 on either side of nose
Why is Visual acuity not a good indicator of the retina?
Can have extensive retinal damage close to fovea or mid-periphery without vision acuity loss
Define static perimetry.
The position and size of stimulus (target) is held constant while the stimulus intensity (brightness) is varied
Define kinetic perimetry.
The intensity and size of the stimulus are held constant while the stimulus is moved from one location to another
Ex: Goldman visual field analyzer
Test different isopters where the size, color, and intensity of the stimulus varied
Ex: bjerrum/tangent screen
Compare central and peripheral field.
Central- portion of the visual field within 30 of fixation
Peripheral- from 30 outwards
Define scotoma.
A localized defect or depression in the visual field
The normal blind spot is an absolute scotoma
Define absolute defect.
A field defect that persists when the maximum stimulus of the testing apparatus is used
Define relative defect.
A field defect that is present to weaker stimulus but disappears when tested with a brighter stimulus
Compare the sensitivity of the fovea compared to the peripheral retina.
Fovea- greatest sensitivity to light (lowest threshold), can see weakest or smallest stimulus
Peripheral retina- less sensitivity to light (higher threshold) needs stronger stimulus
Describe the blind spot on the optic nerve. What is its location?
Insensitive to light (absolute defect)
Optic nerve is nasal to fovea (temporal on VF chart)
Blind spot is on right ride for OD and left side for OS
15.5 temporal to fixation and 1.5 below the horizontal
7.5 and 5.5 (vertical and horizontal dimensions)
What 3 methods can be used to measure confrontation visual fields?
Finger counting
Finger wiggle
Kinetic red
Describe extinction phenomenon.
Patients may have normal VF when single target is presented but when multiple target are present, one of the two stimuli is not detected
Describe finger wiggle to measure CVF.
Two finger are presented on either side of vertical meridian (20 eccentric to fixation in superior and inferior quadrants)
Patient is asked to report which finger wiggled (they should not be oscillated more than 5)
Does have extinction phenomenon
Describe kinetic Red.
No extension phenomenon
5mm diameter red pin is moved inwards
Ask when patient first perceives pin as red
No color vision (cones) in periphery
Which CVF is best to perform? Which is the worst?
Kinetic red is best
Kinetic red and finger wiggle if performing 2
Finger counting is worst (worst sensitivity and specificity)
Where should the target be placed for all CVF tests?
Target should be halfway between practitioner and patient
What is the purpose of the amsler grid? To what extent does the grid test?
To test the integrity of the central visual field (macula)
Test at 30cm where each small square corresponds to 1 degree, so card tests 10 degrees away from fixation in all directions
What is the procedure for amsler gird?
Habitual near Rx
Uniform illumination
Monocular
What do we ask the patient?
Do you see a dot in the center of the grid?
As you look at central dot are you aware of all four corners?
As you look at dot in center, are you aware of all the lines going up and down and side to side?
Are any lines missing, wavy or distorted?
Are any of the lines blurry?
What should we do if patient cannot see center dot on amsler grid?
Switch to dark grid with x going across
Ask patient to fixate where they think the center of the X is
Define metamorphopsia.
Portion of the grid may appear smaller or larger than another portion of the grid or the entire grid may appear smaller or larger when compared to the other eye
Define micropsia.
Portion or entire grid appears smaller
Due to fluid that may spread apart the photoreceptors
Ex: macular edema
Define macropsia.
Portion of the grid or entire grid appears larger
Due to abnormal compression on the photoreceptors
Ex: tumor or mass
What are the effects of ARMD on the amsler grid?
Distortions
Macropsia
What do we record as results for the amsler grid?
No defect noted
If defect found, record size and quadrant, and abnormality
Note any metamotphopsia
Can have patient mark
How can we test a larger portion of the central VF using Amsler grid?
Repeat the amsler grid test, with the patient fixating on the bottom right, left and top right and left corners
This tests 20 degrees away from fixation in all directions
