3.1.5 Investigates the visual fields of patients with all standards of acuity and analyses and interprets the results. Flashcards
Record for Patient with reduced vision was reviewed at V2 and is satisfactory. Had difficulty describing field plots and relating to visual pathway today. Please practice with supervisors and we will assess with further FP
Visual field pathway and understand the field defects that the patient would perceive if the pathway was cut at various points along the visual field pathway?
- Progressing further down the pathway – results in increase congruity i.e., the defects in each eye become more similar i.e., homonymous hemianopia
- Any post-chiasmal lesion will result in defect at the contralateral side i.e., left optic radiation lesion = right homonymous hemianopia
Visual field defect for:
* Optic neuritis
* Pituitary tumour
* Right carotid aneurysm (early and late)
* Pie in the sky
* Pie on the floor
* Altitudinal defect
* Retinal detachment can present as any defect
- Optic neuritis – enlarged blind spot
- Pituitary tumour – compression of nasal fibres at chiasm = bitemporal hemianopia
- Right carotid aneurysm (early and late) – R nasal defect with compression of temporal fibres / binasal defect in later stage
- Pie in the sky – lesion at temporal lobe / Meyers loop causing right homonymous superior quadrantopia
- Pie on the floor – lesion at parietal lobe causing left homonymous inferior quadrantopia
- Altitudinal defect – superior / inferior hemianopia – caused by AAION
- Retinal detachment can present as any defect
Anterior and posterior knee of Willebrand?
- Located at the optic chiasm is the knee of Von Willebrand
- This is where inferior nasal retinal fibres cross the chiasm – but course 4mm anteriorly into the contralateral ON before running posteriorly, A lesion here would result in a junctional scotoma
- i.e. posterior L optic nerve & involvement on inferior nasal crossing fibres of the fellow eye = vision loss in LE, superior temporal defect RE
- Superior nasal fibres dip into the posterior knee of Willebrand
Vertical & horizontal midline
- Retinal lesions will respect horizontal midline due to the distribution of the RNFL layer – with the horizontal raphe dividing the retina into superior and inferior sections
- Neurological defects respect vertical midline due to arrangement of nasal / temporal fibres in pathway
What are the classical glaucomatous field defects and how do these relate to optic disc changes? You should be able to name 6
- Nasal step - damage at the temporal disc with corresponding loss of RNFL; defect is nasal (opposite side from blind spot), can be inferior or superior but will respect midline
- Temporal wedge – defect is at same side as blind spot (less common than nasal step)
- Paracentral (more common in NTG)
- Arcuate scotoma – defect arcs towards disc (RNFL distribution pattern)
- Tunnel vision – end stage with central sparring
- Enlarged blind spot, soft sign
Suprathreshold vs Full threshold
- Threshold = minimum brightness required to evoke a visual response
- Threshold are determined at all stimulus locations using staircase method
- This is more sensitive than suprathreshold
- Enables statistical analysis of visual field because values can be compared with database
- More usual for monitoring progression closely
- Can pick up subtle changes more readily
- Full threshold should be used in glaucoma – more sensitive and with oculus it goes slightly wider
Suprathreshold
- Target is set at a moderate brightness, above expected threshold (based on patients age)
- Recorded as either seen / or note seen
- Does not quantify threshold seen at each point and is less sensitive
- More useful for screening / gross defects
SITA
- Swedish interactive thresholding strategy
- Humphrey field analyser
- Optimises the determination of perimetry threshold by continuously estimating what the expected threshold is based on the patients age & neighbouring thresholds
- It can reduce VF assessment time by up to 50%
- SITA standard – 7 to 9 mins per eye
- SITA fast & SITA faster
Different tests / grid size
24-2
24 degrees from fixation (in 3 directions, 30 degrees nasally)
58 locations over central 25 degrees, extends 30 degrees nasally, pts are 3 degrees apart
2 = at each side of horizontal, no points on horizontal midline
Slightly quicker than 30-2 (reduces test time by 25%)
**30-2 **
30 degrees from fixation (in 4 directions)
76 locations over central 30 degrees, pts are 6 degrees apart
Glaucoma, cataract, neurological
10-2
10 degrees from fixation
69 points, 2 degrees apart
Useful for macular investigation
C40
Central 40 points
Reliability indices
- If >20% the test should be repeated as it is not reliable
- Fixation loses - assessed by presenting suprathreshold targets in the blind spot
- False positive- indicate a trigger-happy patient, responding to the sound of the perimeter when no target is presented
- False negative - patient fails to respond to a suprathreshold target at any given location; associated with fatigue/inattention
- Gaze-tracking – displayed as a chart at the bottom of the page, upward deflections indicate upwards eye movements, downward deflections are recorded when the position of the eye cannot be determined or there is a blink
Single field analysis
- Threshold values at each point
- Grey scale – represents raw decibel sensitivity; darker areas indicating reduced sensitivity
- Total deviation = compares to aged-matched norms for each point
- Pattern deviation = highlights localized loss after correcting for any overall change in the hill of vision i.e., by a cataract
- Glaucoma hemifield test (GHT) analyses the relative symmetry of five pre-defined areas in the superior field to five mirror areas in the inferior field, judging the overall sensitivity
- Classified as being within normal limits, outside normal limits, borderline, abnormally high sensitivity, general reduction of sensitivity
- Oculus also includes a defect curve
Global indices
- Data reduction statistics designed to describe the characteristics of a field plot
- MD (mean deviation) = mean difference in decibels between the normal expected hill of vision and the patients hill of vision
- If deviation out with norm a p value will be given
- PSD (Pattern standard deviation) = takes into account generalised loss i.e., overall depression
- SF = measure of intra-test variance, little clinical significance
Sometimes we refer to Goldmann bowl perimetry - kinetic perimetry technique - what is this and what’s the difference to static perimetry?
- Kinetic Perimetry – Stimulus presented from non-seeing to seeing (light or physical target)
- Optimal stimulus speed 4 degrees per sec
- Points of equal sensitivity form together to make an isopter, different isopters are measured using different stimulus sizes or light intensities or both
- Map contour of hill of vision – smaller targets toward the peak, larger target edge of hill of vision
- Instrumentation – Goldmann Perimeter, Bjerrum Screen, Confrontation Test
*
Esterman
- Binocular assessment for drivers
- Expresses the VF as a percentage of seen targets, presented a suprathreshold level of 10dB
- Binocular Esterman uses 120 pts & favours the inferior visual field
- Available on the HFA
- Patient aligned in the centre – nose lined up with fixation rather than eye
- Habitual driving correction should be worn
- Group 2 – 4 extra pts in the periphery
Common errors
- Inappropriate correcting lens
- Poor alignment
- Poor instructions
- Failing to encourage patient
- Cloverleaf defect – fatigue after initial 4 areas are examined, px performs better at beginning of test and becomes inattentive with time
- Mask defect – steam
- High + can give edge scotoma
Amsler
- Evaluates the central 10 degrees of vision from a focal point (which overall evaluates the central 20 degrees)
- WD 30cm (patient holds)
- +3.25 near add for absolute presbyopes
- Room lights should be on
- Test should be performed monocularly
- Chart 1:
- Patient should be asked if they can see central white dot
- Ask patient to keep looking at dot for remainder of test
- Ask patient if they can see all four sides and corners of the large square
- Ask patient if any of the small squares with the grid are missing or blurred
- Ask patient if any of the lines appear wavy or distorted
- Record – amsler chart: central fields full R and L
Extent of nomal VF:
60 deg up, 75deg inf, 60 deg nasal, 00deg temporal
Causes of VF defect (Medication, rtinal leions and optic nerve causes)
Medication
- Chloroquine (anti-malarial) - central &/or ring scotoma
- Alcohol or Vitamin deficiency - bilateral central, paracentral or centrocecal defect
- Vigabatrin (anti-epileptic) - concentric constriction with binasal predominance
Retinal Lesion
- RP - ring scotoma
- Artery or Vein occlusion
- Retinal detachment - focal defect in affected area
Optic Nerve
- Glaucoma - arcuate, nasal step, paracentral
- Coloboma
- Optic disc drusen - arcuate, enlargement of blindspot
- Optic pit
- Papilloedema
- Optic neuritis - altitudinal, central, peripheral
- Ischeamic optic neuropathy - respect H midline
Total deviation
Difference between the tested sensitivity values and the age-normative data at each retinal location.
1. Numerical map where a positive number relates to a better sensitivity at that location compared to the normal age matched population and with the converse being true for a negative number.
2. Graphical map with four levels of grey at each of the tested locations. The colour of grey represents the likelihood of the retinal location falling within ‘normal’ when compared to the age matched normal population i.e. the darkest grey means that there is a less than 0.5% chance that the retinal location is normal.
3. TD detects global and local changes but does not differentiate between them, therefore there is a risk that a global change may be masking a local defect.
(Total deviation literally measures how much the total the plot has deviated from the norm)
Pattern deviation
adjusts the TD plot to account for any global depression in the visual field sensitivity and therefore highlighting any localised defects i.e. it allows for the differentiation of loss between glaucoma and cataract.
Diff between total and paern deviation
- Total deviation is before hill of vision corrected for - GENERAL LOSS
- Pattern deviation is after hill of vision corrected for - FOCAL LOSS
- Mean deviation is MORE NEGATIVE with worsening defect (GENERAL LOSS)
- Deviation of the visual field values, compared to an age matched normal population.
- On average, 0 to -2dB is normal
- Pattern standard deviation is MORE POSITIVE with worsening defect (FOCAL LOSS)
The Estermann unaccptabl:
- Group 1. Done binocularly. Must have <20% false positives
- Field is 20’ central, 120’ horizontal, 50’ left & right, 20’ up & down
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Unacceptable:
- Cluster of 4 or more adjoining points in central 20’
- Cluster of 3 or more adjoining points 20’ from fixation with single missed points within the central portion
- Extension of qudrantanopia or hemianopia within central 20’ >3 missed points
