Lecture 9: VF/Function Specific Perimetry Flashcards
____ is the central detection and monitoring of visual function in glc
Perimetry
Physiological blind spot is about __ degrees temporal from fixation
15
What is the hill of vision?
- Optic Disc Imaging, RNFL Analysis and Ganglion Cell Analysis
- Axons of the optic nerve fibers are contained in the RNFL
___ is the clincal standard for measuring glaucomatous VF defects
Standard Automated Perimetry (SAP)
- Clinical standard for measuring glc VF defects
- Glaucomatous loss detected/managed more reliably compared to manual perimetry
- Uses static perimetry
- Threshold sensitivity presented in decibels (dB)
- 0 dB = bright intensity
- Values of 30 dB are normal values
- Value are relative and not directly comparable across different makes of perimeters
What is suprathreshold technique
- Relatively quick to administer
- Record whether a location is normal (stimulus seen) or abnormal (not seen)
- Uses a stimulus 4-6dB brighter than expected threshold
- Chooses from age-matched database
- follows expected hill of vision
What is the best technique for glaucoma evaluation? What’s the con of using this test?
Full threshold.. IT TAKES SO LONG to do
- uses 4-2 staircase method
What are the 2 types of full threshold technique? What is the difference between each test?
-
Fastpac
- Reduces test time at the expense of measurement accuracy
-
SITA
- Reduces test time while maintaining standard of accuracy used in 4-2 threshold testing
- Takes about 7 mins per eye
- 2 types: SITA standard & SITA fast
SITA standard is designed for
- Designed for glc - do not use it with other conditions
- Interchanging SITA with conventional full-threshold is not recommended in longitudinal follow up of patients
- SITA is becoming new gold standard for threshold perimetry in glaucoma
- Quicker test is naturally appealing
- Sound research suggests measurement from SITA are in close agreement with full threshold
- SITA defects do appear shallower
SITA FAST is good in subjects who..
have difficulty completeting a long VF test
- Uses larger step sizes
- Makes it even qucker in time
- NOT a great choice for f/u care
- really only use clincailly if pt have difficulty physically/mentally performing standard test
List 5 Patient dependent factors.
What are the other factors? (5)
- Fatigue effect - difficult to control
- Inattentiveness - false negative
- Trigger happy - false positives
- Fixation loss
- Learning Curve
Other factors
- Refractive error
- Trial lens artifact
- Pupil size
- droopy eyelids
- Media opacities/tear film irregularities
Field loss (SAP) is an indicated for what?
advanced disease
If early in disease what test would you order & how often would you repeat testing?
- Baseline 24-2 HVF, consider baseline 10-2
- Repeat at least every 6 months
- Follow the ONH and OCT closely for change
If late in disease what test would you order & how often would you repeating testing?
- Follow the 24-2 VF closely for change
- Repeat at least every 3 months
- May need to follow 10-2 closely as well
- Continue to monitor ONH and OCT
What are the common glaucomatous VF defects?
- Arcuate
- Nasal step
- Paracentral
- Diffuse?
T/F a normal VF does not exclude glaucoma
TRUE, but it does exclude advanced disease
Approximately __ of RGC lost before 5-10DB of VF reduction
40%
fibers from the ___ retina usually most susceptible to damage
temporal
Damaged NFL typically give isolated damage in the ___ areas (__ - __ degrees). Eventually forming ____.
paracentral; 10-20
Arcuate scotomas
Early non-specific changes produces what type of visual field loss?
generalized constriction
Early significant changes produces what type of visual field loss
- Peripheral nasal step
-
Small wing shaped paracentral scotoma
- Within Bjerrum’s area
- Isolated or associated with nasal step
-
Siedel’s sickle-shaped scotoma
- Paracentral scotoma
- Joins blind spot
What does the image represent? Describe each.
- Schematic showing worsening patterns of VF loss in open-angle glaucoma
- A. Location of testing points of 24-2, Humphrey VF
- B. Isolated defects in paracentral area
- C. Small isolated defects combin to form a larger defect
- D,E. Arcuate defect forms and worsens and eventually breaks through to the periphery
- F. End-stage defect, with only small functoinal macular area remaining
What type of VF loss does this represent?
Paracentral scotoma
What type of VF loss does this represent?
Arcuate scotoma (Bjerrum)
What type of VF loss does this represent?
Nasal Step
Quantification procedures applied to VF results can be put into what 3 main categories?
- Analysis of patient response/validity
- Single field analysis
- Series of Visual Field Results (Analysis of Progression)
Various confounding elements may cause misinterpretation of VF results. These confounds can include (6)
- Ptosis
- Patient fatigue
- Small pupils
- Poor alignment
- Trial lens holder artifact
- Co-morbidities creating compound patterns
- e.g. glaucoma ptient with h.o retinal vascular occlusions, optic neuropathies, ARMD, diabetic reninopathy, retinal scarring, strokes
Studies have suggested what 2 things to get a good baseline VF?
- at least 2 field taken about 2 weeeks apart necessary
- If the fields do not show similar results, a third VF taken several months later is useful
What does this image represent? Describe what it is.
- High false positive results produce a “superfield”
- a.k.a “trigger happy” or rambo”
- White areas represent higher than normal decibles on the gray scale
- Characteristic falsely elevated threshold measurements
- Many probability symbols in the pattern deviation map with a normal total deviation map
What is the importance of gaze tracking?
- Record eye movement monitored during test
- also records number of times an eye’s position cannot be determined
- Can only be evaluated subjectively
- Useful for evaluating quality of fixation, particularly when VF defects surround blind spot
What does an upward bar in the gaze tracking chart indicate?
What does the length of the bar indicate?
- upward bar indicates fixation disparity
- the length of the bar represents manitude of disparity from 1 degree to a max of 10 degree
What does a short downard bar represent in gaze tracking?
tracking failure
What does a long downard bar indicate?
indicates eyelid closure
Label the following image
- A. Humphrey field analyzer output showing a single field analysis of results form a glaucomatous patient using the SITA standard program
- B. Reliability indices and test duration is shown in the top of left-hand corner
- C. The results for GHT
- D. global indices are shown below the main gray scale
- E. The total deviation plot
- F. The pattern Deviation plot
- Fixation/Gaze Tracking (bottom image)
What is a single field analysis?
- analysis based a single VF
- compares VF with result from normal population or within eye comparisons
- Block symbols represent different levels of probability with which the particular value would occur in a normal population
- E.g. black symbol: likelihood of a normal subject having that level of vision is <0.5%
- Must be regarded as highly suspect
Fixation losses must be < __ in order to be reliable
- 20% (will be affected by advaned glaucoma or large blind spots
False positive or false negative must be < __-__% in order for VF to be reliable
20-30%
What is the greyscale on the VF used for?
useful for detecting artifacts, overall regions affected and patterns. Also useful for pt education
What is total deviation plot?
- difference (in dB) between test results and normative data for the patient’s age group. shows probability of each point being normal
What is pattern deviation plot?
- Overall sensitivity changes in the hill of vision. Subtracts overall depression value from each test point. Shows localized defects
What is mean deviation?
overal dpression of field. should not exceed -2dB
What is pattern standard deviation (PSD)? What can cause a high PSD?
- Degree of departure from normal hill of vision. High PSD may be due to low reliability or VF defect or BOTH!
What is glaucoma hemifield analysis?
- compare scorresponding point values across the horizontal (upper and lower halves of field)
What is glaucoma hemifield test?
- devised to detect field loss that is asymmetric across the HORIZONTAL meridian - characteristic of glaucomatous loss
Increased variability may be an ealry sign of …?
glaucomatous damage
Hart & Becker proposed that glaucomatous VF go through 3 phases
- Occult: Initial stage with no defect demonstrable despite the fact that occult damage is occurring
- Threshold: period in which shallow defects are often transient and are barely detectable
- Critical phase: VF defects are detectable and progress at an uneven pace to become dense
IN all cases, msut determine whether VF changes are due to what 3 things?
- Noise
- Neuronal damage
- Spurious change due to learning & fatigue
In clinical practice, VF progression is often determined by combination of what 3 things?
- Clinical judgement
- Experience
-
Progression analysis software
- OLDER VERSIONS:
- Mean Deviation Index plotted against time/Glaucoma change probability (GPC)
- NEW VERSIONS:
- Event-based analysis: GPA
- Trend based analysis: VFI
- OLDER VERSIONS:
What is global indices used for? What is the drawback?
- Using mean deviation
- Provides very specifci method for determining change
- if pt shows change in global indices (MD) (PSD), they most certainly have progression
- Drawback: insensitive to early localized change
What is glaucoma progression analysis used for? (GPA)
- Pointwise method
- GPA designed to evaluate change in sensitivity from baseline data
- 2/3 initial fields are merged to give a baseline field
- The change from baseline is displayed at each test location
- Data given in symbols
What is visual field index? (VFI)
- Most recent version of HFA also provides the VFI and VFI progression plot
- VFI is relatively new index that is proposed to better evaluate the rate of progression with SAP
- The aim of this analysis is mainly to provide valuable info on the rate of deterioration of the overall VF
VFI is calculated as… ?
as the percentage of normal VF, after adjustment for age
- VFI of 100% represents a completely normal VF
- VFI of 0% represents a perimetrically blind VF
- The VFI is shown on the GPA printout both as a percentage value for each individual exam and as a trend analysis, plotted against age
What are 3 pros of octopus perimeter?
- Full threshold exam takes less than 2:30 minutes
- 100% eye fixation control if fixation is lost, no stimulus is presented
- Diagnostic programs with test stages prioritize the most crucial field areas
Who makes a good candidate for octopus perimeter? (4)
- h/o poor reliability on HVF
- Inability to sit for duration of HVF
- Equivocal results on previous HVFs
- Glaucoma suspects with clean fields but reason to believe they actually have glaucoma (e.g. poor OCTs, glaucomatous nerves)
What is octopus cluster analysis?
- Designed specifically for glc
- Very sensitive to detection of subtle glaucomatous defects
- VF locations corresponding to same RNFL bundle are grouped and used to calculate a mean cluster defect (cluster MD)
What is Octopus Polar Analysis?
- Projects local VF defects along the nerve fibers to the optic disk and displays them oriented as structural results
- Local defects are projected along the nerve fibers to the optic disc and are represented as red lines
What is octopus defect curve?
- A graphical representation that alerts the clinician to the presence of diffused defects
- Provides a summary of VF and makes it possible to distinguish between local and diffuse defects at a glance
___ remains the most commonly performed method of VF assessment in glc
SAP
- However, studies have shown that in many cases VF defects on SAP are detectable only when a substantial number of RGCs have been lost
Why is there such relative insensitivity of SAP to early RGC damage?
- There is considerable redundancy in teh system
- Light detection can be perceived by all RGC types
- BUT certain features are encoded by certain subsets of RGCs
- Contrast sensitivity
- Movement perception
- Color Vision
RGC are primarily classified by their …?
- projection to the LGN
- Several subcategories
- Morphologically distinct
- Physiologically distinct
What is the goal of function specific perimetry?
- Attempts to isolate subpopulations of ganglion cells by evaluating a specific visual function characteristically processed by that cell type
- When a single system is isolated by the function-specific perimetric test, relatively fewer cells are being tested at the same time
- Less redundancy in the coverage of a given retinal location
- Less overlap in response that could potentially “mask” ganglion cell losses
- Earlier glaucomatous damage becomes easier to detect
Short Wavelength Automated Perimetry (SWAP) is designed to assess what?
- short wavelength sensitive color system
Short Wavelength Automated Perimetry (SWAP) isolates __ cones.
blue cones
- Send projects to blue-cone bipolar cells then project to small bistratified RGCS
- Small bistratified RGCs projects to koniocellular layers of LGN
-
Encode BLUE - YELLOW opponency
- BLUE ON: activates
- YELLOW OFF: suppresses
Before testing with SWAP, the patient should under go what to isolate blue cones?
- adaptation period
- 3 mins
- bright yellow exposure
- fatigues medium and long wavelength cones - isolating blue cones
High risk OHT should be tested with both __ and __
SWAP & SAP
Which one detects VF defects earlier? SWAP or SAP?
SWAP
- Defects detected 3-5 years earlier
- Pt with thinner cornea have higher prevalence of SWAP defects
- Correlation between SWAP and RNFL or optic disc image are stronger (than SAP)
What are some limiations of using SWAP?
- Longer duration of the test
- 15% longer
- Takes 10-15 mins per eye
- Length has been improved by advent of SITA-SWAP BUT
- Still more difficult to recognize a blue target
- Still takes longer
- Still results in more patient fatigue
- Higher test variability
- Both short term (within test) and long term (from test to test)
- Nuclear sclerosis can confound results
- Yellow of lens acts like a blue-blocker
- Adjustment of pattern deviation plot helps
- May not be able to track ADVANCED cases of glc
- Depth of field defects may be so deep that pt can not perceive the target at all
- For ADVANCED glaucoma, conventional SAP should be used
Should you use SAP or SWAP for advanced glaucoma?
SAP
What is frequency doubling technology (FDT)?
- Determines contrast sensitivity for the frequency doubling stimulus
- This phenomenon mediated by subset of magnocellular RGCS
- My cells
- Represent 3-5% of all RGCS
- A deficit would manifest even when small proportion of cells affected due to the reduced redundancy in coverage of a given location of retina
- Results of FDT are predictive of future onset and location of functional loss assessed by SAP
What is the difference between FDT and SAP?
- FDT = predictive of future onset
- able to show functional loss before SAP
- SAP = assess functional loss
How long does FDT threshold and suprathreshold take?
FDT is able to detect progression __ - __ months before SAP
12-24
What are 2 limitations of FDT?
- Large stimulus - reduce ability to detect localized defects
- Low number of targets presented
- evaluating progressive damage over time is difficult
- less valuable for glc f/u
