visual fields Flashcards
what are the type of visual defects
total ipsilateral visual loss
bilateral hemaniopia
left nasal hemianopia
right homonymous hemianopia
left homonymous hemianopia with macular sparing
the more posterior the lesion.
the more congruous the defect
where is the blind spot and why is it important
Blind spot is an important part of visual field assessment.
Can show disease activity.
Can also be used a reliability indicator
what is the binocular visual field
The binocular visual field is the area where both eyes can see the stimulus
It extends approx 60 degrees on either side of the vertical midline
60 degrees superior and 75 degrees inferior
The inferior extent of field is affected by the nose
what is the monocular field of vision
Monocular VF extent
160° horizontally
135° vertically
what is the island of vision
Island of vision in a sea of darkness
Peak = Fovea
Bottomless pit = Blind spot
The sensitivity of the eye is not the same across the whole visual field.
The height of the island represent the sensitivity of the eye and we can see the sensitivity decrease with eccentricity
The peak = fovea with max sensitivity
The VF is described as an island of vision in a sea of darkness
how to examine the visual field
There are 2 types of examination strategies: Kinetic and Static
Kinetic is manual and performed with the Goldmann Perimeter. Automated with Octopus
A stimulus of given size and intensity is moved from outside the visual field towards the center until the patient 1st notice the stimulus
The major advantage of kinetic perimetry is that the examiner has almost complete control over the examination and hence allows for flexibility
Static perimetry is automated and is often performed with the Humphrey Field Analazer
The stimulus is static and is presented pseudo-randomly in the visual field
The major advantage of static perimetry is it is automated, usually faster to perform and does not depend on inter-examiner variability
what are the advantages of kinetic and static methods
Kinetic
e.g. Octopus
More laborious
Requires skilled examiner
Greater flexibility for testing areas of interest
Peripheral VF beyond the central 30 degrees
Static
e.g. Humphrey (HFA)
Faster testing procedures
No inter-examiner variability
Standardised
Central 30 degrees
what part of the visual field to you assess
Measure central, peripheral vision or both?
Central VF assessment
60% of all retinal fibres
Shows most defects caused by ophthalmic disease
Peripheral VF assessment
Perform if pathology is likely to affect peripheral (outside central 30 degrees)
what Is kinetic permietry
The Goldmann perimeter was introduced by Goldmann in 1945
It is a manual instrument, where the patient view inside the bowl and fixate a light in the center, while the examiner sits behind and look through the telescope, to see if Pt maintain good fixation.
The stimuli vary in size which is equivalent to intensity changes of 5dB steps. With each stimulus size an isopter is made
what are the shortcomings of the manual Goldman perimmetry
No longer manufactured
Operator dependent
Lack of standardisation
Intra- & inter-examiner variability
Test-retest variability
Unavailable - alternative Projection perimeter (Takagi)
what is the Isopter map
The isopter map is derived from the technique in which a stimulus of fixed size is moved from outside the island of vision (periphery) which can not be seen until seen
A series of points of equal sensitivity form an isopter
what can be varied on goldmann
stimulus size , intensity and speed
what is semi automated kinetic perimetry
Stimulus size & intensity
Stimulus speed
0°/s (static) or 2°/s - 10°/s (kinetic)
Operator choose start & end points of kinetic stimuli (vectors)
Automatic calculation of isopter and scotoma areas
Reaction time correction
Automatic retest of once established kinetic field
Comparable to manual Goldmann (Rowe and Rowlands, 2014)
Age and reaction time corrected values available (Grobbel et al 2016)
why is the semi automated kinetic perimetry good
Promising test-retest variability
Preferred by patients over static perimetry
Lacking FP,FN and FL reliability indicators
how to examinne field of investigation
Fields of Confrontation
Advantages
Quick, easy
Perform in clinic, wards
Can register as visually impaired on confrontation alone
Valuable in those unable to perform Goldmann / HFA
Children
Disabled
Stroke suffers
Disadvantages
Crude, screening test
how to perform field of confrontation
This a crude technique to screen for any VF defects.
Method: Pt sit facing you approx 1m away. No glasses. The Pt is instructed to look at your nose and cover 1 eye (LE)
You cover your RE, so your VF’s will correspond with theirs
You can introduce target /fingers from the periphery, and Pt is asked to report when seen
You can hold up fingers in each of the 4 quadrants and ask how many fingers seen
Ask to identify face components
Quadrant finger counting
Colour comparison: hold 2 targets 15 degrees from fixation and ask about brightness of 2 red pens
Kinetic boundary testing: white 10-20mm target brought in from periphery
what is the hfa
humphrey filed analyser
Threshold strategies
Estimates the threshold of seeing a stimulus at different test locations
c30-2 / c24-2 / c10-2
Threshold algorithms
SITA
Standard / Fast
what is Sita
The full-threshold algorithm was 1st described by Bebie and Spar (1976)
They concluded the optimum psychophysical strategy was a ‘two reversal staircase’
The step size reduce from 4dB to 2dB after 1st reversal
E.g. if 1st presentation not seen, present stimulus intensity 4dB above, if then seen present 2dB below to ensure sees
Improved FP monitoring. FP is defined as when the patient press the button and no stimulus is presented (trigger happy). SITA use a time window when no patient response is anticipated. The minimum response time is defined as 180msec between presentation of stimulus and patient response and is adjusted according to the individuals response time.
how to interpret grey visual field
When we try to interpret the visual field it is important to look at both the pattern dev plot as well as the grey-scale plot
The grey-scale plot gives us an overview of where the visual field defect is, next to we see the sensitivity values at each test location
The pattern dev plot compare each test location with an age-matched normal database and adjust for the general height of the hill of vision (i.e. diffuse loss) to show localised defects that may be masked by general depression which can be caused by e.g cataract.
So when you monitor a patient it is important to examine any change in the pattern dev plot
The GHT divides the upper and lower field into 5 sectors, and compare upper and lower field to identify any defects
MD is the weighted average of the total deviation values, insensitive to localised loss
The reliability indices can help us to determine how reliable the visual field is.
Fixation loss is determined by counting the number of times the patient press the button when a stimuli is presented as catch trials in the expected physiological blind spot location Fix Loss
False positive means the patient is trigger happy and press the button when there is no stimulus presented
False negative is defined as the number of times the patient fails to respond to a brighter stimulus than has already been seen
When interpreting a VF you should always examine the reliability indices. A visual field is defined as unreliable if the
FL > 20%, FP is >10-15% and/or FN >33%.
High FL may not only be due to the patient is unreliable but can also be caused by misalignment of the blind spot.
High FP error is the best indicator that the patient is unreliable (Newkirk et al. 2006)….
Research has shown that the FN rate increase with increasing depth of the defect
how reliable is the visual field test
Heijl and Bengtsson (1996)
3 types of patients
Little/no learning effect
Greater learning effect between 1st & 2nd visit
Gradual learning curve lasting up to 5 visits
Recommendation for glaucoma
Minimum 2-3 VF ⇨ accept as reliable
Aydin et al (2015) showed a learning effect in normal adults from Turkey
More apparent in those aged >50 years and education below high school
what pts may required a visual field test
Retinal & Optic Nerve Disease
Glaucoma
Optic Neuritis
Anterior Ischemic Optic Neuropathy (AION)
Neurological
Brain tumour e.g. chiasmal compression
Idiopathic Intracranial Hypertension (IIH)
Stroke
Children
In neuro-ophthalmology the aims of perimetry are:
Diagnostic
Monitoring
Functional assessment
glaucoma testing - important - why?
Central threshold testing is recommended for assessing glaucoma (NICE 2017)
Taketani et al (2015) found that approximately 10 visual fields are required to accurately predict progression using HFA 24-2 SITA standard
Aptel et al (2015) progression of visual fields in POAG varies greatly among individuals
describe glaucomatous progression
Early changes
Small paracentral defect
Often supero-nasally
? small degree of diffuse loss
…developing into
Nasal step
Larger arcuate scotoma
Advanced / end-stage loss
‘tunnel vision’
Residual islands in far periphery
describe retinal and optic nerve disease
Optic Neuritis
Inflammatory disorder of optic nerve
Multiple sclerosis
Sudden onset of loss of vision
VF defect represent the effect on the papillomacular bundle
VF defect
Central scotoma
Arcuate defect
Nasal step
Inferior or Superior defect
Complete loss
what neurological conditions may require a visual field test
Idiopathic Intracranial Hypertension (IIH)
Tumour
Orbital
Choroidal melanoma
Optic nerve
Chiasmal compression
Brain
Pituitary adenoma
Medullablastoma
Hypothalmic glioma/astrocytoma
Occipital tumour
Stroke / Vascular
Aneurysm
Thrombosis
Haemorrhage
what are the symptoms of idiopathic intracranial hypertension
IIH
Symptoms
Headaches
Papilloedema
Swellling of optic nerve head secondary to ↑ICP
VF defects
Enlarged blind spot (EBS)
Constricted VF
Nasal loss/arcuate defect
Can correlate with clinical findings and OCT
why is. monitoring of visual fields in idiopathic intracranial hypertension important
Monitoring of VF crucial as visual loss can be subtle, gradual and asymptomatic for a period of time
what are the symptoms of chiasmal lesions
Chiasmal lesion
Symptoms
Headaches, hormonal changes, sexual dysfunction, fatigue, depression
VF defect
Bitemporal hemianopia
Binasal hemianopia is a very rare clinical phenomenon. It is due to bilateral lesions affecting the uncrossed optic fibres within the optic nerve
what visual field defects are associated with stroke
Interruption of the blood supply to a localised area of the brain
Common VF defects
Homonymous hemianopia
Homonymous quadrantanopia
Consider patient’s ability & choose appropriate perimetry test
what is a functional visual field defect
May hear this as malingering – not correct!
Spiralling field
Goldmann or Semi-automated kinetic perimetry
The patient produces a smaller and smaller field as the examination progress.
HFA does not give reliable answers, may be difficult to differentiate from organic VF loss
what may be misdiagnosed as fvl
Most common in teenagers
Typically bilateral and involves both VA and VF.
1/5 had migraine, facial pain, or coexistent organic pathology.
Concomitant psychosocial events were mainly social in children and related to trauma in adults.
Normalization of visual function occurred in a majority of patients.
Early-onset macular dystrophies and hereditary optic neuropathies may be misdiagnosed as FVL.
evlaute examining visual fields in children
manual
Advantages ☺
Better co-op
Allow breaks
Re-check areas
Disadvantages ☹
Qualitative
Lack of standardisation
? reliable for monitoring
Automated (HFA)
Advantages ☺
Quantitative
Standardised testing
Repeatable
Disadvantages ☹
Not designed for children
Boring
Requires good co-op
