Visual Fields Flashcards
What margin is critical for coping in a real environment?
Margin of temporal visual field
What percentage of glaucoma patients have food central vision but pronounced peripheral VF loss?
15-20%
What does peripheral VF loss correlate well with?
Structural loss like nasal optic disc loss
How large is the blind spot and where is it?
- 15 degrees temporal
- 2.5 degrees inferior
- 5 degrees in diameter
What can the blind spot be affected in?
- Glaucoma
- Idiopathic Intracranial Hypertension
Why is the blind spot an important part of VF assessment?
- Can show disease activity
- Can be used as a reliability indicator
How far does the monocular VF extend?
- 160 degrees horizontally
- 135 degrees vertically
How far does the binocular visual field extend?
- 60 degrees either side of the vertical midline
- 135 degrees vertically
How far do the superior/inferior VF extend?
- 60 degrees superiorly
- 75 degrees inferiorly
What are the 2 types of examination strategies for VF?
- Kinetic
- Static
What do we use to perform the Kinetic VF?
- Goldmann/Takagi Projection Perimeter
- Octopus/Twinfield
What do we use to perform the Static VF?
- Automated
- Humphrey Field Analyser (HFA)
How do we perform Kinetic VF?
A stimulus of given size and intensity is moved from outside the visual field towards the center until the patient 1st notice the stimulus. How big the VF is at different intensities of light.
The major advantage of kinetic perimetry is that the examiner has almost complete control over the examination and hence allows for flexibility
How do we perform Static VF?
Static perimetry is automated and is often performed with the Humphrey Field Analyzer
The stimulus is static and is presented pseudo-randomly in the visual field
What is the advantage/disadvantage of kinetic perimetry?
The major advantage of kinetic perimetry is that the examiner has almost complete control over the examination and hence allows for flexibility
- Peripheral VF beyond the central 30 degrees
- Requires a skilled examiner
- More laborious, more time consuming
What is the advantage of static perimetry?
The major advantage of static perimetry is it is automated, usually faster to perform and does not depend on inter-examiner variability (static depends on size and intensity of stimulus)
- Faster testing procedures
- No inter-examiner variability
- Standardised
- Central 30 degrees
What are Static VF tests useful in?
Ocular ophthalmic disease’s like AMD or Glaucoma
What are Kinetic VF tests useful in?
Neurological diseases like pituitary adenoma that affect beyond the central 30 degrees
In pituitary adenoma what VF area goes first?
Superior VF tests go first in the peripheral VF
What % of retinal fibres go to the central VF?
60% of all retinal fibres and thus show most defects caused by ophthalmic disease
What are the manual and semi-automated types of kinetic perimetry?
- Manual type
Goldmann or Takagi - Semi-Automated
Octopus (Haag-Streit) replaced the Goldmann
How does the Goldmann work?
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 disadvantages of Goldmann’s perimetry? What was developed in its place?
- No longer manufactured
- Operator dependent
- Lack of standardisation
Intra- & inter-examiner variability
Test-retest variability - Unavailable - alternative Projection perimeter (Takagi)
A semi-automated kinetic perimeter
What do we normally set a VF machine to?
IV - 3 - E
What is 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
Colours = intensity of the light and speed of target
Compare with shaded area of colours i.e. inferior nasal and superior temporal quadrants in central VF are compressed
See slides 17 & 18
What do the roman numerials on an (semi) automated (Goldmann & Octopus) VF machine relate to?
Diameter of target
What do the numbers and letters relate to on VF?
Intensity of the light
What is the stimulus speed in VF?
0°/s (static) or 2°/s - 10°/s (kinetic)
What are some benefits of semi-automated kinetic perimetry?
- 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)
If we compare the Humphrey 850 and Octopus 900 what do we find?
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
Octopus 900 better peripheral VF test, particularly in superior and inferior VF than the Humphrey 850 (better practicality as a neurological VF test)
How do we conduct Fields 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 are the advantages of the Fields 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
What Threshold strategies does the Humphrey Field Analyzer (HFA) have?
- Estimates threshold of seeing a stimulus at different test locations
- c/30-2
c/24-2
c10-2
What are the threshold algorithms of the Humphrey Field Analyzer (HFA)?
SITA (standard, fast, faster)
What does C30-2 mean
Central 30 degrees
What does SITA stand for?
Swedish Interactive Threshold Algorithms (SITA)
- Bengtsson & Heijl (1997)
How is the SITA standard conducted?
4 primary points are presented and then the remainder are based on neighbouring points using pseudo-random stimulus presentation
- One reversal staircase procedure
- 4dB steps…reversal…2dB steps
- Prior knowledge “models” of normal & glaucomatous VF’s
- Response time monitoring
What is the two reversal staircase method in the SITA standard?
- 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
How does the SITA standard account for response time?
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 is the SITA fast conducted?
Unlike standard doing 4dB steps, SITA fast is less accurate (fewer stimulus exposures) doing 3dB steps but cognitively could be beneficial for patients OR if really busy in clinic
How do we measure poor reliability on Humphrey?
- FL >20% (fixation loss)
- FP >20% (false positives)
- FN >33% (false negatives)
What does GHT stand for?
Glaucoma hemifield test (tells you the likelihood of glaucoma)
What does MD stand for in VF tests?
Mean deviation should be between 0 and -2 to be considered “normal”
What does fixation loss mean?
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
What does false positive mean in VF testing?
False positive means the patient is trigger happy and press the button when there is no stimulus presented
What does false negative mean in VF testing?
False negative is defined as the number of times the patient fails to respond to a brighter stimulus than has already been seen
See slide 30
What did Heijl and Bengtsson (1996) find out about the reliability of VF tests?
Heijl and Bengtsson showed there is 3 types of patients: a small number of patients show little or no learning effect, the majority of patients show the greatest learning effect b/w 1st and 2nd visit, and a smaller group of patients shows a gradual learning curve which can last up to 5 visits.
Hence the general agreed recommendation for confirming glaucomatous VF defects is that the patient has to perform at least 2-3 VF before being reliable VF.
How do we optimally set up patients for VF testing?
- 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
What patients may require a VF test?
Retinal & Optic Nerve Disease
- Glaucoma
- Optic Neuritis (presents in MS)
- Anterior Ischemic Optic Neuropathy (AION)
Neurological
- Brain tumour e.g. chiasmal compression
- Idiopathic Intracranial Hypertension (IIH)
Stroke
Children
What are the aims of perimetry in neuro-ophthalmology?
- Diagnostic
- Monitoring
- Functional Assessment
How do we use VF to predict glaucoma progression?
Taketani et al (2015) found that approximately 10 visual fields are required to accurately predict progression using HFA 24-2 SITA standard
What early changes to do we seen in glaucomatous progression?
- Small paracentral defect
- Often supero-nasally
Develops into:
- Nasal step
- Larger arcuate (due to arc pattern) scotoma
What are the advanced/end-stage loss in glaucomatous progression?
- ‘Tunnel vision’
- Residual island in far periphery
What is Optic Neuritis?
- Inflammatory disorder of optic nerve
- Common in MS
What is a sudden onset loss of vision?
- VF defect represent the effect on the papillomacular bundle
What are some neurological disorders that VF might affect?
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 symptoms of IIH?
IIH = Idiopathic Intracranial Hypertension
Neurological
- Symptoms = headaches
- Papilloedema = swelling of optic nerve head secondary to increased intracranial pressure
- VF defects = Enlarged blind spot (EBS), constricted VF and nasal loss/arcuate defect
- Can correlate with clinical findings and OCT
What are the symptoms and VF defects in Chiasmal lesions?
Symptoms
- Headaches, hormonal changes, sexual dysfunction, fatigue, depression
VF defect
- Bitemporal hemianopia
What is a stroke and how are the VF’s affected?
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
How is functional visual field loss shown in perimetry?
The patient produces a smaller and smaller field as the examination progress (spiralling field) on Goldmann or Semi-Automated kinetic perimetry
HFA does not give reliable answers, may be difficult to differentiate from organic VF loss
What did Lim, Siatkowski and Farris (2005) find about functional visual loss and VFs?
- 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.
What are the advantages and disadvantages of using manual VF testing for children?
Advantages ☺
- Better co-op
- Allow breaks
- Re-check areas
Disadvantages ☹
- Qualitative
- Lack of standardisation
- ? reliable for monitoring
What are the advantages and disadvantages of using automated (HFA) VF testing for children?
Advantages ☺
- Quantitative
- Standardised testing
- Repeatable
Disadvantages ☹
- Not designed for children
- Boring
- Requires good co-op
Why must we be cautious when looking at VF tests done on children?
Be cautious when interpreting data in children<13 years
2/3 of 10-12 year olds were reliable but only 23% between 5-9 years
( Slides 46 & 47)
What does Field of BSV give us that’s different to information gained in the Hess Charts?
The field of BSV gives different information to the Hess Chart. During the plotting of the field of BSV fusion is being maintained and thus the size of field is dependent not only on the defect in movement but also on fusional amplitudes.
