VF Interpretation Flashcards
How are fixation losses monitored
Gaze tracking and blind spot monitoring
Gaze tracking
- located at the bottom of the chart
- records deviation from correct fixation as upward deflections
- downward spikes are eyelids or eyelashes interrupting view (blink)
- if the FL rate exceeds 20% it is flagged
Blind spot monitoring
- number of time a patient responds to a target placed in the blind split
- 10% of all stimulus is presented in the blind splint areas
Numeric grid
- ther threshold sensitivities measured at each test point
- indicated in Db
- 0 dB indicates the max brightness target available for that test
- numbers should be the greates in the center, less in periphery
- look for abnormally high or low values
- even if <0 does not mean blind, they couldn’t see that target
Grayscale printout
- appx of field
- patient education
- resembles Isopters in a gray tone
- little clinical relevance
- SHOULD NOT BE USED IN THE ANALYSIS OF THE FIELD
Total deviation plot (dB); upper plot
- appears as numbers and graphics in the central left area of the print out
- represents the difference between the measured threshold of each individual test location and the age corrected normal value for that location
Negative total deviation plot upper plot
Indicate sensitivities which are below the median age corrected sensitivities
Positive values for the total deviation plot upper plant
Indicate sensitivities which are above the medial age corrected sensitivity
Total deviation plot; lower plot
- plots the significance of deviations found in the upper plot
- using a small dot for a point within the range of 95% of the normal values or with a shaded box (outside of 95% of normal values indicating suspicion for abnormality)
- see p value
Most common reasons for overall reduction or generalized depressions in the total deviation plot
Cataracts
Incorrect trial lenses
Poor test takers
Pattern deviation plot
- takes the total deviation plot and adjusts it upwards to downwards to screen out generalized depression
- highlights only significant localized visual field loss
- uses ther same symbols as the total deviation plot to show points which are significantly worse than normal (p value)
- single most useful analysis on the SFA printout
- highlights subtly, but significant localized variations that might otherwise be masked
- early defects show up sooner on pattern probability map than on grayscale
Total deviation vs pattern deviation
- if total deviation plot and pattern deviation plot are about the same, the there is little to no generalize loss
- if abnormal TD plot and normal PD plot=cataract, incorrect Rx, etc
- if abnormal TD plot and abnormal PD plot=trigger happy. Abnormally high sensitivity
P value (probablitle plots)
-sensitivities are worse then those found in 5%, 2%, 1%, and o.5% of normal patietns with the same age as the patient being tested are highlighted with corresponding symptoms
Glaucoma hemififled test
- compares pattern deviations probability scores in 5 zones in the upper field to mirror image zones in the lower field
- sensitivity differences between upper and lower hemiofields are a hallmark of glaucomtous field loss
Language classifications of threshold
- outside normal limits
- borderline
- generalized depression of sensitivity or abnormally high sensitivity
- within normal limits
Glaucoma respects the ____ midline
Horizontal
Neuro probs respect the ______ midline
Vertical
Outside normal limits in GHT
Sensitivities in one or more Tom the five zones in the upper half of the field are significantly different from the sensitivities measured in corresponding zones int he lower half of the field
P=0.5
Means there is a 95% confidence
GHT: borderline
- zone pairs differ by an amount greater than what is seen in most normal patietns (P<0.03)
- does not reach the levels required for outside normal limits
GHT: generalized depression of sensitive or abnormality high sensitivity
-best test point locations are either so low or so high that those levels are only see in 0.5% of normal patietns
Withint nornal limits on GHT
Pretend when none of the above limits are reached
Global indices on VF printout
- found on the lower right hand corner printout
- single number representations of the VF
- mean deviation
- pattern standard deviation
- short term fluctuations
- corrected pattern standard deviation
Mean dedication
- shows how much on average the whole field departs from normal
- zaverage departure (+ or -) of each test locatio nfro mthe age corrected nornal value (+MD=Better than average, -MD=less than average)
- abnormal = P<0.5%
- less than 0,5% of the population has a mean deviation larger than the value found on the test
- height of hill of vision compared to age matched normals
PSD on VF printout
- measures the extend to which the threshold determinants at different locations differ from each other
- does not change with media (cataract)
- the higher the PSD, the more irregular the pattern
- high PSD-more localized defects-more indicative pathology
- indicates the shape of the hill of vision
VF I
Age corrected assessment, expressed as a percentage
100%=periemtricallt normal, 0%=perimetrically blind
Used for progression analysis
Artifacts to look out for
Eyelid and brow ptosis
Incorrect refractive error
Eyelid and brow ptosis
This can cause a dense superior fdefect along the superior edge points. Pateitns with visual significant ptosis may bee fit from having their eyelids taped for testing
Incorrect refractive error
This can lead to a generalized depression in sensitivity that may mimic that of a cataract
- high refractive error can create a magnification or minification effect and require proper vertex distance calculations
- using the wrong lens power sign or not using the new refractive erro after a patient has cataract surgery are two common errors
Rim artifacts
The position of the trial lens holder can lead to a rim artifact if it is too far from the patietns eye, creating a full or partial ring scotoma
Patient fatigue artificial
- this may manifest with longer test times, high false negative value or preferentially abnormal peripheral senestivityy
- lobular ring or cloverleaf pattern
Interpretation and report and VF
- look at both fields together
- look at field in relation to other clinical findings, does this info make sense
- evaluate reliability: make sure the data is trustworthy
- evaluate defect; type of defect
- repeatability of any defect
- probably diagnosis
Recognizing VF defects
Graysascel not appropriate For making Dx, must concentrate on -deviation plots -global indices -attention to Raw (threshold) data
Documetniaon of VF
- make statements referencing reliability
- make statement regarding pattern, depth, and size of VF loss
- make statements which correlates other exam findings with the VF
- always remember to write signature next to statements
Reliable baseline
Establish a reliable baseline VF is cructoal in the manangemt and future monitoring for possible progression of a VF defect
Clinicians should obtain at least _____ repordubule basleine VF to detect smaller increments of change
Two
Evaluating change in VF allows the practitioner
To determine if the condition is stable, progressing or improving
VF and assessment and plan
Statistically and clinically significant changes on the VF allow the practictional to make the necessary changes to the patietns treatment and management plan
Follow up and VF
Use the same test strategy and pattern to allow easier comparison and monitoring and progression
Evaluating the VF involves determine whether the field is normal or if ant progression/improvement has occurred between ______ fields
Two or more
Standard printouts should include
- the pattern and strategy utilized
- pt name, DOB, date of exam, pupil diamter, VA, correction used
- size of stimulus used, fixation target (central versus diamond patter), testing time, fixation losses
- false positive and negative repsosne, degree of response fluctuations
STATPAC
- computerized analysis package with the HVF
- simplifies field interpretation by differentiating between nornal and abnormal fields
- determines if a patietns field results fall within the range or normal for his/her age
- compares test results with the patients own baseline from earlier test to determine if the observed change I’d larger than typically seen on follow testing
STATPAC single field analysis (SFA)
- compares the results of a single threshold test with age corrected normative data
- highlights any sensitivity values of patterns that deviate significantl from normal
- presents patietns demographic data, indices of test reliability and raw test results
HVF: interpretation and report
- reliability parameters
- raw test results
- deviations plots
- GHT
- global indices
Where are the realizability parameters found
Found in the upper left hand corner of the printout
- fixation losses: FL
- false positive errors: FP
- false negative errors: FN
False positives
- refers to the number of times a patient responds and no target is presented
- flagged if it exceeds 33%
- theses patients are also identified as abnormally high sensitivity message on GHT
- note: if the false positive erro exceeds 15% the field is considered unrealized and should be re run
False negatives
- refers to the numbers of times a pateitn fails to repsosnd to a suprathreshold target placed in a seeing area of the VF-pateitn does not respond to a stimulus that is brighter than what they have already seen
- flagged if it exceeds 33%
