Visual Fields Flashcards
Do you do VF dilated or undilated?
Undilated
Indications for a visual field
- performed as part of a comprehensive eye exam
- examination may not have access to a perimetric instrument
- perimetry is reserved for selected patients
Advantages of confrontational visual fields
- simplicity
- flexibility
- requires no specialized instrumentation
Disadvantages of confrontational visual field
- can not determine the exact size of field loss (QUALITATIVE)
- Lack of standardization
- not sensitive enough to detect subtle defects
How does the computer present stimuli in static perimetry
Random fashion
What us important for the random presentation in the static perimetry
Speed
What does static perimetry allow for
Storage of data
What is the most widely used instrument for VF
Humphrey visual field
What is the gold standard of visual field
Humphrey visual field
What do you do if you get abnormal findings on a patient?
Repeat test 2-3 times to make sure they are accurate
What quantifies the degree of reduction of sensitivity at each point tested
Target presentation: threshold
What is most helpful in following defects over time
Target presentation: Threshold
Provides a detailed map of each eyes deficit
Target presentation: threshold
What are the threshold strategies
- full threshold
- full threshold from prior data
- fast threshold
What is the standard for VF
SITA
This still uses method of determining threshold values for 4 primary points in each quadrant
SITA
These are used to generate starting levels of neighboring points
SITA
The result of this is that threshold determination is reached in a shorter amount of time, but with the same accuracy as a full threshold test, monitors test point results and utilizes a complex statistical technique which assigns a level of confidence for how close each point is
SITA
What is the main difference between SITA standard vs SITA fast
Levels of confidence the program needs to stop testing at a particular point
SITSA standard and certainty
Sets a higher level of certainty whihc requires more trials at a given point thus, it is more accurate
Which is more accurate, SITA standard vs SITA fast
SITA standard
Whihc takes less time, SITA standard or SITA fast
SITA fast
HVF indications
- suspected VF defect
- retinal disease (RP)
- neuro-ophthalmic disease
- glaucoma
What is a good reason to do central 10
Retinitis pigmentosa
Advantages to Humphrey VF
- test administration is more standaradized
- minimizes test variability
- improves readability
Disadvantages to Humphrey VF
- expensive equipment
- very tedious for certain patients (fatigue)
- requires strong knowledge of data interpretation by the examiner
Advantages to automated perimetry: screening
- portable and compact
- affordable
- no trial lens or eye patch
- high level of sensitivity and specificity
- rapid assessment of the field
- reduced learning curve
Disadvantages to automated perimetry: screening Zeiss FDT
- results limited by cataract and pupils < 3 mm
- trouble detecting small scotoms die to the fact that the FDT uses larger test targets
- offers fewer testing points vs HVF
Advantages to Humphrey matrix automated perimetry: screening
- instrumentation occupies less office space
- high level of sensitivity and specificity
- provides a relatively rapid assessment of the field
- target sizes have been reduced to allow for better detection of small scotomas
Disadvantages of Humphrey matrix FDT automated perimetry: screening
Currently all studies are conducting using the HVF-it is still the gold standard in today’s practice
Factors that include VF measurement
- uncorrected refractive error
- pupil size
- media
- facial structure
How do uncorrected refractive error affect VF field measurement
Will reduce threshold sensitivities causing the field to look artificially depressed. The affect of the blur is greater with small stimuli presented centrally than with larger peripheral stimuli
How does pupil size affect VF measurements
Pupil diameter less than 2.5mm can cause a decrease in retinal adaptation and in turn, retinal sensitivity . Will increase the impact of central media opacities
How does media affect VF readings
- cataracts, vitreal, and corneal opacities may decrease the actual light coming in
- results in depression of Isoptera and exaggeration of known defects
How does facial structure affect VF measurement
A drooping eyelid, prominent brow, a large nose can all cause peripheral field defects
What are patient factors that will influence VF measurement
- age/speed of reaction
- attention/fixation
- understanding of test procedures/instructions
- learning curve
- all factors must be considered when choosing a VF testing strategy
How does age/speed of reaction affect VF measurement
- older individuals may respond more slowly to a presented stimulus= high false negative reading
- younger or anxious patients may respond too vigorously=high false positive result (trigger happy)
How does attention/fixation affect VF measurements
- gaze tracking: upward deflections=gazes away from fixation while downward deflections=result of a blink
- cloverleaf=threshold values are normal around the 4 primary points where testing beings, but are greatly reduced at other locations where the threshold is measured later in the test
How does understanding the test procedures/instructions for the patient affect VF results
May result in a patient failing to respond when the stimulus is presented
-may yield high loss of fixation
How does a learning curve affect VF results
May cause initial field to show an overall midperipheral depression or include focal defects all of which resolve on subsequent field testing as the patient gains experience with the test
Supervision during VF testing
- must monitor carefully
- promoting the patient on fixation and attention can greatly improve test reliability and results
If tests are not improved with greater supervision or additional testing
One may consider altering testing strategy
What test is purely qualitative
Confrontation fields
What test is purely quantitative
Automated perimetry
What is the order of tests from purely qualitative to purely quantitative
- confrontational VF
- tangent screen
- Goldman perimetry
- automated perimetry
Advances of tangent screen test
Low cost
Simple to operate
Flexibility
Disadvantage of tangent screen test
- reproducibility
- backlight variability
- does not assess peripheral VF
- difficult to detect fixation loss
When is the Goldmann perimetry helpful
When the visual defect is located or extends beyond the central 30 degrees (peripheral VF defect)
Advantages of goldmann peripmerty
- can rapidly evaluate the peripheral visual field
- useful for localization characterization of neurological defects
Disadvantages of goldmann perimetry
- requires a high level of patient cooperation
- requires a highly trained perimetrist
- perimetrist will affect test results
- may not recognize early field defects
