O2B Visual Fields
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Why do we assess visual fields?
- Assess peripheral vision
- Assess the integrity of the visual pathway
- Diagnose ocular and neurological diseases
- Monitor the progression of ocular diseases
What are the indications of the assessment of visual fields?
- Glaucoma / suspicion of glaucoma
- Reduced visual acuity
- Unexplained headaches
- Neurological disorders
- Benign optic disc conditions
- Retinal disorders – inflammations and dystrophies
- Assessing fitness to drive
- Evaluating sport fitness especially elite levels
What are the advantages of visual field assessments?
- Direct assessment of visual function
- More than just central vision
- Can typically detect cheating
- Repeatable examination techniques – good for monitoring progression
- Good for differential diagnoses of diseases – typically obtain characteristic VF losses
- Extra income for practitioner
What are the disadvantages of visual field assessments?
- Machines not portable
- Expensive equipment
- Time consuming
- Subjective assessment by patient
What are the bones that restrict vision?
- Superior margin = frontal
- Inferior margin = maxillary
- Medial margin = frontal lacrimal and maxillary
- Temporal margin = frontal and zygomatic
How does sensitivity vary within the visual field?
- adaptation level
- nature of stimulus test
What are the characteristics of the island of vision?
- steeper on the nasally
- steeper superiorly
What is the hill of vision?
- 2D section of the island of vision
- 0-5- steep slope at fovea
- 5-40- flatter central VF
- >40- steep edge of VF
Diffuse visual field loss / Depression – generally caused by pre-retinal opacities e.g. corneal oedema, cataract
Gap in HOV?
- Focal visual field loss - An area of reduced sensitivity surrounded by an area of normal sensitivity – focal point of damage in retina or visual pathway
- Relative scotoma
- Absolute scotoma
Visual field contraction – caused by conditions which affect the peripheral retina
What are the manual ways of VF testing?
- amsler grid
- tangent screen
What are the advantages of manually testing VF?
- Fast and flexible
- Good for measuring severe VF loss or measuring absolute loss
- Good for multiple handicapped
- Excellent in low vision and neurological cases
What are the disadvantages of manually testing VF?
- It’s not standardized
- Not good for measuring the depth of scotoma
- Can’t pick up shallow scotomas well
- Not as good in quantifying central field
- Requires an experienced clinician
What are confrontational fields?
- Relatively gross method used to screen for the presence of unsuspected field defects- insensitive
- compares px VF to practioners
What are the types of confrontational field tests?
- target confrontation: dynamic movement of small target in VF until seen
- finger wriggling: dynamic movement of fingers in VF until seen
- finger counting:
What is a manual VF test?
stim presentation and manipulation is controlled by practioner
What is a kinetic VF examination strategy?
- a stimulus of constant size and shape is moved across VF
- moved frmo periphery until seen
What is a static VF examination strategy?
stim apears in stationary loactions but may change in characteristics
What is a threshold exam?
estimate threshod of eye at different locations
Whats is a suprathreshold exam?
present stim above threshold/ recrod if seen
What is a tangent screen?
- more sensitive than confrontational
- Non-reflective black screen
- Small central white fixation target
- Concentric circles stitched at
- 5 intervals
- A selection of targets
How does the tangent screen work?
- px sits 1m away-tests 25-30deg
- target is moved from periphery until seen- scotomas
What is an Amsler grid?
- black lines on white bg
- viewed at 28cm, one box= one degree
- wavy lines/missing lines
What area of visual space does the amsler grid test?
10 degree either side of fixation
What does the amsler grid primarily test and how?
- macular damage: AMD, diabetic maculopathy, central serous retinopathy
- sees wavy lines or lines missing
What is the Goldmann bowl perimeter?
- Stimuli projected onto the surface of a bowl
- Stimulus can becontrolled by the practitioner
- A stylus which moves in conjunction with the control of the stimulus can mark field extend on pre-printed chart paper
What is the Friedmann VF analyser?
- Presents 2,3 or 4 stimuli in VF
- Patients report how many lights they saw
- Light intensity can be altered using filters
- Results are marked on a pre-printed sheet
What is a HVFA?
- tests sensitivity for specific points in the peripheral visual field
- px presses on the button when they see the stimulus
- different colours, size and intensities are displayed
What is medmont automated perimetry?
similar to HVFA but on PC
how does retinal ganglion cell function related to visual field loss?
- P-80, M+K:10
- less redundancy, more noticealbe in MK cells
What is SWAP?
- based on K cell pathway
- decreased sensitivity to blue wavelength
- more sensitive to glaucomatous changes
- yellow-background- is used to de-sensitise the red and green cones
- affected by older ppl- yellowing of lens
What is flicker perimetry?
- based on M cell pathway
- CFF- constant contrast
- TMP- contrast is varied
What is FDT?
- Sinusoidal grating of low spatial frequency undergoes rapid counterphase flicker at high temporal frequency
- Stimulus appears to have twice the spatial frequency
- removes low spatial frequencies
- Patient must detect the presence of a ring – the core of the ring is brighter and the inner and outside edges darker
What is MERG?
- records the electrical activity from 50-100 areas of the retina – electrodes either near the cornea or striate cortex
What are the 3 variations in stimulus size?
- Angular subtense
- physical size
- goldmann size
What is angular subtense?
- a variation in stimulus size
- relative size of the retina is the same for all testing distances
What is the physical size variation in stimuli?
relative size of retina will vary according to testing distance
What is the goldmann size?
size replicates that unsed in the goldmann bowl perimeter
Intensity vs sensitivity relationship?
greater the sensitivity of the eye, the lower the intensity of light for the threshold and the lower the stimulus intensity
- In perimetry- how bright the background and stimulus appear
Stimulus and background intensity relationship?
intensities are measured in log scale - decibels
What is Bloch's law and how does it relate to the stimulus presentation time?
- luminance x duration = constant
- at a critical duration time, the brightness of the stimulus is proportional to the luminance and duration of the stimulus= temporal summation
What is the ideal stimulus presentation time?
- >100ms: reduces temporal summation
- <250ms: reaction time for the saccade of the eye to move to the periphery
What are 3 factors that affect the gradient of the seeing curve?
- increase in px experience= steeper cruve and increased reliability
- decreased sensitvity in the eye: increased variability
What are screneing tests?
tests whether the points are seen 6dB brighter than threshold of HOV
What are the types of screening tests?
- 2 zone: all points either seen or not
- 3 zone: points that are missed are retested at max
- quantify defects: points missed retested for threshold value
What is a full threshold testing?
- measured at 4 locations, each quadrant 9 deg away from fovea
- 2 reversal staircase: 4dB reduced to 2dB when results become positive
- threshold= dimmest light seen
What is FAST PAC?
- one reversal: single step 3 dB
- reduces testing time by 2/3rd
- less accurate
What is SITA?
- Relies on prior knowledge
- number of false positives
- will adjust presentation rate according to px response rate
What is SITA standard?
What is SITA Fast?
3db single reservsal
What is the protocol 1 threshold test?
- point grid falls on H + V axis
- shit cos leaves 6 deg gap of test points at fixation
Why is protocol 2 preferred?
- 3 degree gap at macula- smaller
- test on either side of midline
What are the HFVA tests that are available?
- 10-2: 68 pt grid spaced 2 deg apart- macula+ advanced glaucoma
- 24-2: 54 pt grid spaced 6 deg 30 deg nasally- glaucoma ONH
- 30-2: 76 pt grid 6 deg spacing- glaucoma, retina, ONH
- 60-4: 68 pt grid 30-60 deg- retinal changes, glaucoma
- Macula: 16 pt grid, 2 deg spacing, 5deg fovea
- Nasal step: 60 deg from fovea- glaucoma
What is the test selection choice for the retina periphery?
full field to 60 deg
What is the test selection for the macula?
central vision testing- 10, 24 or 32 deg
What is the test selection for glaucoma?
- early: 24-2
- advanced: 10-2 more central due to loss of peripheral
What are some of the human factors that affect testing?
- pupils: small, depressed
- Age: older= dec retinal, cisual pathway, senile miosis
- learning effect: increased performance= increased exp
- increased sensitivity= dec variability
- media opacities: dec retinal contrast
- fatigue: difficulties in attention
- anatomy: lids, spinal problem, prominent brow
What is the cutof for false positive results?
- greater than 30%
- trigger happy
What is the cutoff for false negative results?
- greater than 30%
- inattention/adfanvced field loss
What are sensitivity values?
compares measured sensitivity to age matched norms/HOV?
What is probaility plot?
sensitiviy at each point below norms/HOV?
What does a negative mean deriation mean?
- loss in sensitivity
- generall loss or smeall area of depression
What does a small/large pattern deviation mean?
- small: diffuse loss
- large: focal loss
MD- normal, PSD normal
MD- abnormal, PSD- normal?
generalised loss of sensitivity
MD normal, PSD abdnormal?
Small localised defect
MD abnormal, PSD abnormal?
large defects + localised component
averages resting of same point: varibility testing
Corrected pattern standard deviation?
- index sensitive to focal loss
- separates real deviation from theose due to variability
What is the glaucoma hemifield test?
decides if field loss is compatible with glaucoma diagnosis
What are considered abnormal results?
a point/cluster of points decreased in sensitivity that is repeatable
What is considered an abnormal result on the hymphrey?
glaucoma hemifield test norm- VF loss is compatible with glaucoma, PSD<5%
VF abnormal results?
- single point p<0.5%
- 2 clustered points: p<5%, one point p<1%
- 3 or more points: p<5% + pattern of loss consistent with ocular pathlology
What is a sector scotoma?
damage to large bundle of fibres: field loss reflects pathway
What is a arculate scotoma?
- eg glaucoma
- damate to specific bundles of fibres
What is a centrocoeal scotoma
- toxic amblyopia
- bilaterally due to tobacco/alcohol nutritional amblyopia
- damage to papillomacular bundle
Damage to PRs?
- irregular field loss of rod/cone dystrophy: binocluar
- e.g. retinitis pigmentosa: damage to REP/PR- contricted fields
Damage to outer retina?
monocular- doent respect midline, rpe damage
What is a central scotoma?
- e.g. arm
- damage at rpe, relative/absolute defect
What is a large monocular scotoma?
- e.g. retinal detachment
- damage doens't follow bundles of fibre and midline
What is a titled optic disc and how does it affect the visual field?
- congenital defect, nasal bilateral
- relative temporal defect: doesnt respect vertical midline
- papilloedema: non- inflammatory swelling, ONHby increased intra cranial pressure- bilaterally enlarged blind spot
What is an optic nerve head drusen and how does it affect the visual field?
- formed by accumulation of deposits- calcified mitochondria
- congenital defect: bilateral
- arcuate defec: drusen pressures nerve fibre bundles
- arcuate scotoma: specific bundles damaged
How does a tumour at the pituitary gland affect the visual field?
- presses onto the optic chiasm
- nasal fibres affected first, then all
How does haemorrhages and aneuryms at the circle of willis affect the visual field?
affects left of chiasm- LE temporal retinal fibres - affects nasal field
How do the fibres direct in the optic tract?
- superior fibres: medial
- inferior fibres: temporal
- macular fibres: centre
- incongruent: anterior
- congruent: posterior
How does the LGN affect the visual field?
visual field defect increases in congruency, more posteriorly
Optic radiations and visual field?
- field defects:
- pie in the sky
- pie on the floor
- increased in congruency, more posterior the fibres
V1 lesions visual field?
- vascular: congruent, more posterior
- tumour: slow progression
- trauma: physical damage can affect one or both hemispheres
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