Static automated perimetry Flashcards
What happens in static perimetry?
the stimulus is stationary but chages in its intensity until the sensitivity of the eye at that point is found
is measured at preselected locations in the VF
What are the 4 options for program selection for static automated perimetry?
- central 30 degrees
- 24 degrees
- 10 degrees
- full field
What are 2 different types of static automated perimetry tests in aumated perimetry?
- suprathreshold tests
- threshold testing
What are suprathreshold static automated perimetry tests?
screening tests - calculate threshold adjusted for age by testing a few predefined spots using a 4-6dB step
What is an advantage and disadvantage of suprathreshold static automated perimetry tests?
- advantage: quickest to perform (screening tests)
- disadvantage: may miss subtle variations in the scotoma’s contour, as they do not go on to map defects
What should suprathreshold static automated perimetry tests not be used for?
glaucoma monitoring
How does threshold testing for static automated perimetry work?
steps of 4dB are used until detected, then retested at this point in 2dB steps
What is the gold standard static automated perimetry test for monitoring glaucoma?
threshold testing
What are 2 things required for threshold static automated perimetry?
patient cooperation
patient concentration
What phenomenon can be seen in threshold static automated perimetry?
appreciable subject learning curve
What are 2 advantages and 1 disadvantage of Humphrey perimetry?
advantages: sensitive, reproducible
disadvantage: difficult to perform
What does Humphrey perimetry broadly involve?
fixation monitoring - by tracking gaze and retesting the blind spot
How is calibration of the Humphrey perimetry machine achieved?
automatically calibrates itself on startup
What are the 3 options for selection of programes on the Humphrey perimetry device?
- Threshold (full threshold or SITA central 30-2, 24-2, 10-2)
- Suprathreshold testing (sreening central 76 point, full field 120 point, Esterman DVLA visual standard)
- Coloured stimuli
What is the name of the DVLA visual driving standard test setting on the Humphrey perimetry device?
Esterman
What are 4 things to take into consideration when analysing the results of automated perimetry?
- reliability indices
- absolute retinal thresholds
- comparison wih age-matched controls
- overall performance indices (global indices)
What are 3 examples of reliability indices (subject reliabiility)?
- fixation losses
- false positives
- false negatives
What are fixation losses?
fixation plotted, if patient moves and machine retests and patient seens spot, a fixation loss is recorded.
What degree of fixation losses may compromise automated perimetry?
fixation losses above 20% may significantly compromise the test
What are false positives in automated perimetry?
patient responds to normal whirr of the computer noise when it sounds, as if it is about to present a light but does not - high false positive occurs in trigger happy patients
What are false negatives in automated perimetry?
brighter light is presented in an area in whcih the threshold has already been determined and the patient does not see it.
In which type of patients does a high false negative score in automated perimetry occur?
fatigued or inattentive patients
What are 10 examples of common visual field abnormalities?
- Altitudinal field defects
- Arcuate scotoma
- Binasal field defect
- Bitemporal hemianopia
- Central scotoma
- Homonymous hemianopia
- Constriction of peripheral fields
- Blind spot enlargement
- Pie in the sky
- Pie on the floor
What are 5 examples of causes of altitudinal field defects?
- ischaemic optic neuropathy
- hemibranch retinal artery or vein occlusion
- glaucoma
- optic nerve or chiasmal lesions
- optic nerve coloboma
What are 3 examples of causes of arcuate scotomas?
- glaucoma
- ischaemic optic neuropathy
- optic disc drusen
What are 5 causes of a binasal field defect?
- glaucoma
- bitemporal retinal disease (e.g. RP)
- bilateral occipital disease
- compressive lesion of both optic nerves or chiasm
- functional visual loss
What are 3 causes of bitemporal hemianopia?
- chiasmal lesions
- tilted optic discs
- sectoral RP
What are 4 causes of central scotomas?
- macular lesions
- optic neuritis
- optic atrophy
- occipital cortex lesions
What are 2 causes of homonymous hemianopia?
- optic tract or lateral geniculate lesions
- temporal, parietal or occipital lobe lesions
What are 7 causes of constriction of peripheral fields?
- glaucoma
- retinal disease (e.g. RP)
- bilateral panretinal photocoagulation (PRP)
- CRAO
- bilateral occipital lobe lesions with macular sparing
- papilloedema
- functional visual loss (spiraling or crossing of the isopters)
What are 6 causes of blind spot enlargement?
- papilloedema
- glaucoma
- optic nerve drusen
- optic nerve coloboma
- myelinated nerve fibres
- myopic discs
What cause a pie in the sky lesion?
temporal lobe lesion
What causes a pie on the floor VF defect?
parietal lobe lesion
What are probability values in automated perimetry?
indicate the significance of the defect (<5%, <2%, <1% and 0.5%)
lower p value, greater clinical significnt nd lesser likelihood of defect having occurred by chance
What are 4 types of global indices (i.e. a summary of the results of automated perimetry as a single number used to monitor change)?
- Mean deviation
- Pattern standard deviation
- Short-term fluctuation (SF)
- Corrected PSD
What is pattern standard deviation (PSD) a measure of?
focal loss or variability within the field, taking into account any generalised depression
What does a higher pattern standard deviation (PSD) indicate more so than mean deviation (MD)?
more indicative of glaucomatous field loss than MD (mean deviation)
What is mean deviation (MD) a measure of?
overall field loss
What is short-term fluctuation a measure of?
indication of the consistency of responses; assessed by measuring threshold twice at ten preselected points and calculated on the difference between 1st and 2nd measurements
What is corrected pattern standard deviation (PSD) a measure of?
variability within the field after correcting for SF (intra-test variability)
What are the 4 types of typical graphical results from automated perimetry?
- grey scale
- numerical display
- total deviation
- pattern deviation
What does the grey scale graphical result from automated perimetry indicate?
decreasing sensitivity represented by darker tones. grey scale tones correspond to 5dB change in threshold
What does the numerical display graphical result from automated perimetry indicate?
Gives the threshold for all points checked (in dB).
Bracketed results show the initial test if the sensitivity
was 5dB less sensitive than expected
What idoes the total deviation graphical display from automated perimetry represent?
Calculated by comparing the patient’s measurements
with age-matched controls. Upper chart is in dB, and
lower is in grey scale
What idoes the pattern deviation graphical display from automated perimetry represent?
Adjusted for any generalized depression in the overall
field. This highlights focal depressions in the field, which
might be masked by generalized depressions in sensitivity
(e.g. cataract and corneal opacities)
What visual field defect do the combined graphs show a typical example of?
R eye of patient with glaucoma - nasal step and developing superior arcuate field defect
What are 4 types of automated perimetry protocols?
- Swedish interactive threshold algorithm (SITA; fast or standard)
- Esterman grid
- Short wavelength automated perimetry
- Frequency doubling perimetry
What was the purpose of development of SITA protocols?
strategies were reated to take 50% less time than conventional algorithsm to perform, thus increasing reliability
How are SITA perimetry protocols carried out?
using prior information and establishing threshold values more quickly
What are 3 different types of Esterman grids available?
- central field
- whole field
- binocular field
How does the Esterman grid protocol work?
subjects are tested and a percentage score of functional field is given
What is the binocular Esterman grid field test used for?
by DVLA as a measure of visual disability for drivers
Is it necessary for subejcts to see all the points on the Esterman binocular grid for DVLA testing?
no
How does short wavelength automated perimetry work?
uses standard static threshold testing strategies with a blue test object on a yellow background (red and green cones desensitised by adapting the eye to yellow light)
How does short wavelength automated perimetry work?
uses standard static threshold testing strategies with a blue test object on a yellow background (red and green cones desensitised by adapting the eye to yellow light)
In what situation is there a particular advantage to using short wavelength automated perimetry?
may be omre sensitive than conventional white-on-white perimetry to early glaucomatous damage
What are 4 issues with short wavelength automated perimetry?
- increased total test time
- difficulty to set up test
- high short-term fluctuation (SF)
- data affected by lens opacities
What does frequency doubling perimetry measure?
the function of a subset of specialised retinal ganglion cells (large magnocellular M cell pathway fibres) by rapid reversal of broad black and white bars, creating a doubling frequency illusion
What is thought to happen to M-fibres in a certain pathological state?
thought to be lost early in glaucoma
What is a particular use for frequency doubling perimetry and why?
glaucoma screening; high sensitivity and specificity
What are 3 advantages of frequency doubling perimetry?
- high sensitivity and specificity
- small portable unit that is not sensitive to background illumination levels
- reported to work independently of refractive errors up to +- 7D
