Visual fields Flashcards
What are the components of the visual pathway
The visual pathway consists of the retina, optic nerves, optic chiasm, optic tracts, lateral geniculate bodies, optic radiations, and visual cortex.
Types of visual pathway defects
Total RE/LE visual loss
Bitemporal hemianopia
Left nasal hemianopia
Right homonymous hemianopia
Left homonymous hemianopia with macular sparing
More posterior the lesion…
the more congruous the defect
What is a congruous visual field defect
identical between the two eyes
What is a incongruous visual field defect
it differs in appearance between the eyes
Adenoma can cause
bitemporal hemianopia
What is a bitemporal hemianopia
describes the ocular defect that leads to impaired peripheral vision in the outer temporal halves of the visual field of each eye
What is a nasal hemianopia
Loss of vision of one nasal field (the right field of the left eye or the left field of the right eye) resulting from damage to the lateral region of the optic chiasm
What is a homonymous hemianopia
A field loss deficit in the same halves of the visual field of each eye
Blind spot is usually
15 degree temporal
2.5 degree inferior,
diameter 5 degree
Importance of blind spot assessment
Blind spot is an important part of visual field assessment.
Can show disease activity.
Can also be used a reliability indicator
Which conditions cause a large blind spot
IIH and brain tumour
What is binocular visual field
The area where both eyes can see the stimulus NOT field of BSV
It extends approx 60 degrees on either side of the vertical midline
60 degrees superior and 75 degrees inferior
What is the inferior extent of the field affected by
The nose
What is the monocular VF extent
160° horizontally
135° vertically
What is the binocular VF extent
60° on either side of vertical midline
135° vertically
Island of vision describes…
Island of vision in a sea of darkness
Peak = Fovea
Bottomless pit = Blind spot
Is the sensitivity of the eye the same across the whole VF
No
The peak = fovea with max sensitivity
The VF is described as an island of vision in a sea of darkness
Why does the VA drop as you extend from the fovea
Density of rods and cones
Methods of assessing VF
Kinetic and Static
Examples of kinetic VF
Manual/ semi-automated
Goldmann/Takagi Projection Perimeter
Octopus/ Twinfield
Examples of static VF
Automated
Humphrey Field Analyzer (HFA)
Advantages of kinetic VF
e.g. Octopus
More longer and laborious
Requires skilled examiner
Greater flexibility for testing areas of interest
Peripheral VF beyond the central 30 degrees
Advantages of static VF
e.g. Humphrey (HFA)
Faster testing procedures
No inter-examiner variability
Standardised
Central 30 degrees
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)
Disadvantages of manual Goldmann perimetry
No longer manufactured
Operator dependent
Lack of standardisation
Intra- & inter-examiner variability
Test-retest variability
Unavailable - alternative Projection perimeter (Takagi)
What is the semi automated kinetic perimeter
It has been developed to overcome this shortcomings. It can assess pituitary tumour patients VF and improvement post surgery which is variable
Examples- Octopus, manual and semi-automatic operation
Kinetic periphery involves
An 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
Circles are called isopters
Brighter light is easier to see than dimmer/ smaller light- these variables allow us to assess different parts of VF
Numbers show intensity of light
To look at periphery use of smaller and dimmer target- relates back to hill of vision
To detect smallest light need to be at fovea anything brighter is seen in peripheral VF
Shaded area is where line should be – this patient could have slight ealry stages temporal visual field defect- there is a relative defect due to it only being detected on the inner field and due to the dimmer intensity
Brighter light can hide this
What is an isopter dependent on
stimulus size and intensity
Hill of vision and Isopter relationship
Test different light intendity due to sensitivity
- Can adjust target size
What are the variables of stimulus
Size- biggest size 1.7 degree for low vision patients
Intensity - Intensity can be combined with stimulus size
Speed
Speed of stimulus
Speed of when target is sent into patients visual field
Fired from outer to central position
Can double check areas of blindess and moving the stimulus
Scotoma is area of vision loss
Semi automated kinetic perimetry features
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)
Comparing Humphrey 850 and Octopus 900
Previous knowledge- Static and kinetic perimetry options are commonly used in the diagnosis and monitoring of ocular disease.
Recent knowledge- Rowe et al 2019 found
Humphrey kinetic perimetry is a useful option but may underestimate or miss visual field loss in peripheral superior/inferior visual field due to ceiling effects
Another method of examining/ screening VF defects
Fields of confrontation
Field of confrontation +/-
+ 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
- Crude and gross screening test
Fields of confrontation method
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 Swedish Interactive Threshold Algorithms (SITA)
Staircase procedure for detecting light intensity
SITA standard
one reversal staircase procedure
4dB steps…reversal…2dB steps
Prior knowledge “models” of normal & glaucomatous VF’s
Response time monitoring
SITA standard
4 primary points
Initial primary values based on normals
Remainder based on neighboring points
Pseudo-random stimulus presentation
SITA fast- aims
Shorter test duration
3dB steps…reversal…1dB steps
Fewer stimulus exposures & shorter testing time⇒
Less reliable
What does the Humphrey visual analyser do (HFA)
Estimates the threshold of seeing a stimulus at different test locations
c30-2 / c24-2 / c10-2
But full threshold and fastpac are the forerunners to the strategy generally used today called SITA
Interpreting results
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
Pattern deviation 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.
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
GPA- glaucoma change probability map and glaucoma alert
Reliability- indices can help us to determine how reliable the visual field is
Fixation Loss- 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 >20%
False Positive >20%
False Negative >33%
Poor reliability
How reliable is the VF test
There is a learning affect
What is the optimal testing of patients
Set-up
Chin rest
Comfortable
See patient’s eye on video monitor
Careful & standardised instruction
Ensure can see fixation target clearly through large lenses
Correct near prescription
Do not use patient’s own glasses!
Tape upper lid if ‘droopy’
DEMO…
Only test if understands task
Which patients require a VF 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
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
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
Types of tumour
-Orbital
Choroidal melanoma
-Optic nerve
Chiasmal compression
-Brain
Pituitary adenoma
Medullablastoma
Hypothalmic glioma/astrocytoma
Occipital tumour
Types of stroke/ vascular events
Aneurysm
Thrombosis
Haemorrhage
Investigating 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
Monitoring of VF crucial as visual loss can be subtle, gradual and asymptomatic for a period of time
Enlarges blind spot – neurological
Needs to be assessed
Optic nerve will look pale if there are signs of disease- due to not enough oxygen which causes death of optic nerve fibres
Important to assess as it cab be critical referral
What is a 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
Bitemporal hemianopia – in picture and seen in optic chiasm
People don’t know that they have pituaortory tumours – can feel tires, low mood
Stroke VF defects
Interruption of the blood supply to a localised area of the brain
Common VF defects
Homonymous hemianopia- most common
Homonymous quadrantanopia
Consider patient’s ability & choose appropriate perimetry test
Functional VF loss
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
Findings of visual loss
Farris B et al 2005 found
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.
VF in children- manual pros and cons
Pros ☺
Better co-op
Allow breaks
Re-check areas
Cons ☹
Qualitative
Lack of standardisation
? reliable for monitoring
VF in children- automated (HFA) pros and cons
Pros ☺
Quantitative
Standardised testing
Repeatable
Cons ☹
Not designed for children
Boring
Requires good co-op
Comparing HFA and semi automated kinetic periphery
Humphrey Field Analyzer
-A real challenge
-False positives and Fixation losses high in children 10 years or younger
Semi-automated kinetic perimetry
-Octopus
