Visual Field Assessment

The essential elements and terms of visual field assessments

The Visual Field

• Sensitivity of different retina areas to light stimuli > peripheral vision

• All the space that one eye can see at any given instant.

  • Tate and Lynn 1977

  • ‘Space’ to highlight that eyes look at three-dimensional volume rather than two dimensional surfaces

• Three -dimensional space is often translated into two dimensions

  • photographs

• The sensitivity of the retina varies

  • Macula most sensitive

  • Periphery less sensitive

  • ONH – blind spot

• The sensitivity of the retina varies with light level

  • Light conditions

  • Dark conditions

  • Low light conditions

• The measurement of this sensitivity is also dependent on the stimulus used while measuring it

• Normal extent of the visual field (monocularly)

  • More temporally than nasally

  • More inferiorly than superiorly

• Facial contours influence extent

  • Limited by the bridge of the nose and the extent of the brow

The visual field is tested ________ and is more temporally and inferior.

Monocularly

The Visual Field

• Both eyes open

  • Horizontally field has an extent of 200º

  • Overlap of 120°

• Binocular Field

  • Where both eyes can see the stimulus

  • 60 degrees either side of the vertical midline

  • 60 degrees up

  • 75 degrees down

• Inferiorly the binocular field is affect by the nose

The overlap field is _______.

120 degrees

Hill of Vision

• Most sensitive

  • Fovea

• Least sensitive

  • Blind spot (black bar)

• This slice is along the horizontal

High point of the hill is the ______ and it is located closer to the nasal side.

Fovea

Blind Spot

• Vertical oval 8.5 x 5.5 degrees

• Located 15.5 degrees temporal to fixation and 1.5 degrees below the horizontal midline

• Absolute

• Relative

The blind spot is an area in your field of vision where you cannot_____.

See

Why Measure VF?

• Evaluation of the peripheral retinal function

• Evaluation of the neural pathway function

• Evaluation of function of higher centres of the brain which process visual information

• Functional problems anywhere on the visual pathway can have a pattern which is indefinable and specific

• As part of a comprehensive eye examination

• Retina lesions

  • Glaucoma

  • Toxic amblyopia

• Optic nerve lesions (e.g., optic neuritis)

• Diseases affecting visual pathway

  • Stroke, tumours, inflammation

• Conditions exhibit specific VF patterns

• Evaluation of normal vision

• Evaluation of abnormal vision

• Monitoring normal or abnormal vision for change

  • Improvement

  • Deterioration

• Finding the island of vision for each eye

• If there is damage to the right cortex it will be apparent in the left visual field of both eyes

• If there is damage to the left cortex it will be apparent in the right visual field of both eyes

Measuring the visual field is important is it evaluates peripheral retinal function, ________ function, and brain centres for visual processing.

Neural Pathway

Factors Affecting VF Results

• Facial contour

• Thick spectacle frames

• Myopia, Hyperopia

• Pupil size

• Media opacity

• Px fatigue

• Malingering

These are all things that could affect visual field results. True or False?

True

The Visual Pathway

• Information collected by the retina exits the eye through the optic nerve

• The optic nerve leads to the optic chiasm where the optic nerves meet

  • Information from the left visual field passes to the right lateral geniculate nucleus

  • Information from the right visual field passes to the left lateral geniculate nucleus (LGN)

• From the LGN the information goes via the optic radiations to the primary visual cortex

• The optic chiasm sorts nerves according to the information they will carry

• The left visual cortex receives information from both eyes but one visual field

• The right visual cortex receives information from both eyes but one visual field

• This sorting of nerves helps us locate where visual field defects originate from

Each visual cortex receives information from both eye but only ______ visual field.

One

• Origin of defects

  • Anterior to the chiasm field defects respect the horizontal midline

  • Posterior to the chiasm field defects respect the vertical midline

• The exceptions

  • Macula sparing - the preservation of central vision, specifically the macula, despite damage to the visual cortex

  • In the retina

  • In the cortex

The _______, ________ & _______ are exceptions to being origins of VF defects.

Macula Sparing; Retina; Cortex

• Central Scotoma - a blind spot or area of reduced vision that appears in the central part of the visual field

• Monocular Vision Loss - the inability to see with one eye

• Bitemporal Hemianopia - a condition where vision is impaired in the outer (temporal) halves of both visual fields.

• Contralateral Homonymous Hemianopia - a visual field loss where the same half of the visual field is affected in both eyes

• Contralateral Superior Quadrantopia - a visual field defect where a person loses vision in the upper quadrant of their field of view (on the same side)

• Contralateral Inferior Quadrantopia - a visual field defect where a person loses vision in the lower quadrant of their field of view (on the same side)

• Contralateral Homonymous Hemianopia with Macular Sparing - a visual field defect where vision is lost in one half of the visual field on both eyes (same side), but the central vision (macula) is preserved.

Contralateral VF defects are normally on the same side. True or False?

True

Strategy Types:

• Kinetic perimetry: Stimuli of a set size and intensity moves through the field.

  • The size of the stimuli can be varied

  • The intensity of the stimuli can be varied

  • The presentation time can vary

    • Speed of movement of the stimuli through the field

• Goldmann perimetry (1945) is a manual, kinetic visual field test that assesses an individual's peripheral vision by having them indicate when a moving light stimulus enters their field of view

• Static perimetry: Each stimulus is at a fixed point on the background

  • The size of the stimuli can vary (generally doesn’t)

  • The intensity of the stimuli can vary

  • The presentation time can vary

• Flicker-perimetry (less common nowadays)

• ‘Frequency doubling technology (FDT) perimetry is based on a flicker illusion created by counterphase flickering of a low spatial frequency sinusoidal grating at a high temporal frequency. This phenomenon essentially creates an image that appears double its actual spatial frequency.’

Goldmann perimetry is a ______ VF tests.

Kinetic

Photometric Background

• Units of illumination

  • How much light is falling on a surface

  • Not perceived by the eye

• Units of luminance

  • How bright something appears (perceived by the eye)

  • How a surface emits or reflects light

  • Units for luminance cd/m2 or apostolibs (1cd/m2=3.14 asb)

• Photopic conditions

  • Mesopic conditions (dusk) – reduces cone activity and flattens peak

  • Scotopic conditions (night)-external isopter widens due to increased rod response and a central depression due to lack of rods

• Modern perimeter use a background luminance in the low photopic range

• Visual deficits are not all apparent at the same light levels

• Retinal sensitivity fluctuates even when stabilised

  • Fluctuation more with a shallow profile

  • Time to adapt to dark condition (scotopic) takes longer that for photopic conditions

• Ambient light levels in clinical areas are difficult to control

  • Brighter background luminance is insensitive to these fluctuations

• Higher background luminance (photopic) have a shorter time to adapt to

  • Most tests have chosen 10cd/m2=31.5abs

______ is how bright something appears to the eye

Luminance

How the Visual Field is Measured

• Stimulus intensity against a background intensity

• The stimulus can be varied

  • Position in the field

  • Size

  • Intensity (brightness)

  • Presentation time

  • Colour

The stimulus can be varied (SCIPP). True or False?

True

Insensity vs Sensitivity

• When measuring fields we are interested in how bright the stimulus and background appear to the eye

• For a stimulus to be visible, the luminance of the stimulus has to be greater than the luminance of the background

• The intensity of the stimulus that is detectable from a background is described as sensitivity

  • The stimulus has intensity

  • The eye has sensitivity

The stimulus has _______ and the eye has ______.

Intensity; Sensitivity

Position of Stimuli

• Described by eccentricity from the fixation point

  • Where the patient looks when performing the test

• Fixation point relates to the fovea

The eccentricity from the fixation point is the distance from the fixtion point. True or False?

True

Size of Stimuli

• Can be described in terms of

  • Equivalent to Goldmann bowl perimeter target size

  • Diameter in mm

  • the angle subtended at the eye

• Is situated in the background surface

  • Flat

  • Bowl (curved)

• Converting stimulus diameter into the angle subtended the testing distance needs to be known (usually around 33cm)

• There is a simple relationship between a stimuli size and the sensitivity needed for the eye to see it

• Spatial summation

  • The larger the size the easier it is to see

  • The lower the threshold

• Neural elements in the retina sum information

  • Bright small stimulus

  • Large dim stimulus

• Spatial summation varies across the retina

• In the dark adapted eye

  • 30 minutes of arc at the fovea

  • 60 minutes of arc in the periphery

• In the light adapted eye summation and eccentricity are linear in relationship

• Ricco’s Law - Luminance x Area = Constant

______means the the larger the size the easier it is to see and the lower the threshold. Bright ______ stimulus and Dim ______stimulus.

Spatial summation; Small; Large

Stimuli Presentation Time

• A stimulus can appear brighter the longer it is presented

  • Critical duration time summation

  • This time has a limit though

• Critical Duration of Vision

  • Human eye ~100ms

• Luminance and duration relationship according to Bloch’s law

• There is no addition to the brightness of the stimulus to presenting it for longer after this critical duration

• Bloch’s Law - Luminance x Duration = Constant

• Most stimuli have a presentation time of 200ms

• Temporal summation and critical duration vary

  • stimulus size

  • Background luminance

  • Retinal location

• The larger the stimulus the shorter the critical duration

• The higher the background luminance the shorter the critical duration

• If the presentation time of a stimulus is longer than the critical duration then it is only necessary to specify a stimulus luminance

• We have strong reactions to look at stimuli

  • A reflex

  • The orientating reflex

• This saccade takes about 250ms

• The ideal presentation time

  • Longer than 100ms

  • Shorter than 250ms

• Most fields tests use a presentation time of 200ms

• If the stimulus is too fast or too slow it can be missed and seem smaller than it is.

The ideal stimulus presentation time is longer than ______ but shorter than _____.

100ms; 250ms

Stimulus Sensitivity

• Intensity = how bright a stimulus is

• Given as luminance • How much light is given out

• The intensity of a stimulus tells us about how sensitive the retina the light is falling on, is able to detect it

  • As the stimulus gets dimmer the eye needs to be more sensitive to be able to detect it

• Sensitivity within the visual field is the inverse of stimulus intensity

• As the sensitivity of the eye goes up it is capable of seeing dimmer and dimmer stimuli

• Sensitivity of the eye is therefore described in terms of how dim the stimulus is

  • By the stimulus intensity (i.e., luminance)

  • Unit: decibel (dB)

  • 0dB=10,000asb to 51dB=0.08asb (stimulus intensity)

• Sensitivity is described as the dimmest stimulus (1dB) seen according to that stimulus’s intensity

• The limit of sensitivity is described as the threshold

  • The Fovea is most sensitive in normal room illumination

• Limit of foveal vision: 40 dB

• Limit Normal vision range: 20 dB to 38 dB

• Limit Typical range of abnormal vision: 0dB to 30 dB

• Limit Maximum perimeter brightness: 0dB

Sensitivity is the dimmest stimulus or smallest _______ seen according to the stimulus’ intensity.

Decibel

Why Decibels not Apostilbs?

• Luminance

  • Stimulus intensity

  • Apostilbs

• Sensitivity

  • Retinal locations

  • Decibels (dB)

Sensitivity scale (dB)

• Decibel scales go up as the intensity scale goes down

• High sensitivities are therefore represented by higher numbers

• Eye works in a log not linear manner

Decibel scales go up as the intensity scale ______.

Goes Down

Standard ________ are commonly used in automated static

perimetry and have two reversals.

Standard Staircase

Visual field machines use either full threshold or supra threshold algorithms

The HFA uses _________ algorithm and the staircase endpoint is __________.

The Octopus uses _________ algorithm, and the staircase endpoint is _________.

The Henson uses ________algorithm, and the staircase endpoint is _________.

SITA (Swedish Interactive Threshold Algorithm); Last Seen Value; GATE (German Adaptive Threshold Estimation); Average of Last Seen and Last Unseen; ZATA (Zippy Adaptive Threshold Algorithm); Termination After a Set of Numbers

Single or Multiple Stimulus:

• Single stimulus

  • Locations change

  • Stimulus intensity changes

• Full threshold tests present single stimulus and gather information at a location at a time

• Suprathreshold tests are estimating field ‘goodness’ or ‘badness’

• Suprathreshold tests lend themselves to screening

  • Sifting the (probably) normal from the (probably) abnormal

  • Speed is of the essence

• Multiple stimuli strategies take half the time for the same number of stimuli

• The price of a quicker test is accuracy

• The price of accuracy is an increased testing time

• Multiple stimulus strategies have to balance

  • The extent of the supra threshold increment

  • The accuracy of the initial threshold element

  • The time taken for the initial threshold measurement

Suprathreshold tests are mostly for ________.

Screening

Static visual fields are either ______ or _______.

Full threshold; Suprathreshold

• Monocular Vision Loss - the inability to see with one eye

• Bitemporal Hemianopia - a condition where vision is impaired in the outer (temporal) halves of both visual fields.

• Contralateral Homonymous Hemianopia - a visual field loss where the same half of the visual field is affected in both eyes

• Contralateral Superior Quadrantopia - a visual field defect where a person loses vision in the upper quadrant of their field of view (on the same side)

• Contralateral Inferior Quadrantopia - a visual field defect where a person loses vision in the lower quadrant of their field of view (on the same side)

Neoplasm and inflammatory process cause _______, _______ and _______.

Contralateral Homonymous Hemianopia; Contralateral Superior Quadrantopia; Contralateral Inferior Quadrantopia

The neural organisation in the retina is relative to the ________.

Horizontal

Glaucoma

• The most common reason for a visual field defect is glaucoma

• Progressive optic nerve damage with characteristic visual field changes

  • Nasal step -a relative depression or loss of vision in the nasal (towards the nose) part of the visual field, especially along the horizontal meridian (the imaginary line running across the center of the field

  • Arcuate - a specific pattern of visual field loss, often associated with glaucoma, where there's a "step" or a sudden drop in vision along the horizontal meridian

  • Paracentral - a specific pattern of vision loss where a "step" or "drop" in sensitivity occurs near the center of the visual field, within about 10 degrees of the point of fixation

• Overall depression of the field (in the end stages)

• Typically first evident within the central 30o

• In the binocular visual field the locations of defects are usually ..

  • Where the information from the two eyes overlap, and therefore ..

  • Symptomless until advanced

The most common reason for a visual field defect is _______.

Glaucoma

Disc Edema shows an enlarged _______.

Blind Spot

For diabetic macula edema a 10-2 can be done. It is a type of full-threshold test thatassesses the central 10 degrees of the visual field with 68 closely spaced points. True or False?

True

For _________, ________ and _________ a full threshold 30-2 test could be done

Central Serous Chorioretinopathy; Diabetic Retinopathy; Optic Neuritis

Optic Neuritis can cause a ____________ VF defect.

Central Scatoma

A _____________ can cause a bitemporal hemianopia.

Pituitary Adenoma

3rd Cranial Nerve Palsy and Pituitary Adenoma can cause a bitemporal qaundrantanopia. True or False?

True

Metastasis can cause Left Contralateral Homonymous Hemianopia and it can be assessed using the full threshold _________ test.

30-2

A stroke can cause a Homonymous superior quadrantanopia (pie in the sky) visual field defect.True or False?

True

Confrontation VF

• Gross fields test, manual method

• Kinetic/static strategy

• Gross field defects

  • Recent onset hemianopia

  • Recent onset quadrantanopias

  • Field results that don’t make sense

  • Artefacts

  • Poor witnesses

• Confrontation procedure

  • Examiner sits directly opposite patient, 1m away

  • One eye should be occluded

  • Examiners eye on the same side should be occluded

  • Examiner introduces a target and compares own field with patient’s field

    • Finger counting (static)

    • Hat pin (kinetic)

• Quick screening and domiciliary exams

• Examiner compares own VF to that of patient

• Target moved in flat plane

• Note any changes in fixation

• Can be performed anywhere

• Can detect extinction phenomenon

• Sensitivity is low 50-60%

Confrontation VF has low sensitivity. True or False?

True

Assessment of the Central 10 Degrees (Amsler)

• Paper or electronic based

• Central defects can be mapped

• High rate of false positives

• Distortion reported with no active pathology

• Simple and quick

• Good aide memoir for monitoring for change

• 10cm square subdivided into 20X20 square

• Each box represents 1 degree at 30cm.

• Wear NV spectacles

• Sensitive to macular pathology

• With the chart at 30cm away

• Monocularly tested

• Near correction used

• Fixate on the central spot

• Describe if any of the lines are distorted or broken

• Questions: can you see the central dot? Can you see all four quadrants whilst looking at the dot? Looking at the dot- are any lines wavy or missing? Do any squares appear strange (blurry, moving, different colour)?

The amsler test is done at 30cm away. True or False?

True

Artefacts and Extraneous Factors

• There are a number of common artefacts that confound field results

• Test related

  • Defocus

  • Lens artefacts

  • Fixation

  • Adaptation

• Patient related

  • Pupil size

  • Lids and Brows

  • Fatigue

  • Learning effects

• There are a number of other factors to take into account

  • Age

  • Angioscotoma

The are numerous artefacts that affect VF results. True or False?

True

The abolsute scotoma is the _________ and it is 15 degrees temporally to fixation.

Blind Spot

The Henson 900 is a ___________ stimuli VF test.

Multiple

Humphrey Fields Analyser (HFA)

• Automated

• Patient presses the button when they see the light

• HFA Screening Strategies

• Central 40 Point Screening Pattern

  • C-40

• Central 64 Point Screening Pattern

  • C-64

• Central 76 Point Screening Test Pattern

  • C-76

• Full Field HFA

  • HFA Central 81

  • HFA Central 120

  • HFA Central 135

  • HFA Central 246

HFA is automated. True or False?

True

• Suprathreshold without Quantification

  • Seen

  • Missed

• Suprathreshold with repeat

  • Real miss?

• Suprathreshold with Quantification

  • Missed stimuli presented at a higher intensity increment

  • In specific categories (steps)

  • Full threshold strategy

Go to fullthreshold when no supra has passed. True or False?

True

Visual Field and Driving - Esterman

• ‘Functional scoring system' is the current gold standard for testing binocular visual fields

• Used by many national driving authorities

• UK: px declares eye condition according to ‘driving eyesight rules’ and will get a notification from DVLA

• Esterman test

  • Automated suprathreshold test

  • Single very bright stimuli (10dB)

  • 120 locations within the visual field

  • Spread over +/-75o horizontally

  • 35o superiorly

  • 55o inferiorly

  • Patient fixates centrally

  • Test time of around 4 to 5 minutes

• Group 1 license

  • A minimum horizontal fields of vision of 120o , horizontally 50 degree left and right and 20 degree up and down

  • no significant defect within 20o of fixation

• 'Pass’ Esterman protocol

  • Scattered single missed points

  • A single cluster of up to three contiguous points

• Significant central loss (Fail)

  • A cluster of four or more contiguous points that is either wholly or partly within the central 20o area

  • Loss consisting of both, a single cluster of three contiguous missed points up to and including 20o from fixation and any addition separate missed points with the central area

  • Central loss of any size that is an extension of an hemianopia or quadrantanopia

To pass you can’t miss more than a cluster of 3 points. True or False?

True

Testing Algorithims in Static Strategies

• A process or set of rules to be followed in calculations or other problem solving operations

• Visual fields use either threshold or supra threshold algorithms

• Threshold

  • Measures the intensity of the dimmest stimulus which can be tested/seen 50% of the time at each test location

• Full Threshold

  • Estimate of threshold at a whole series of different retinal locations

  • Monitoring extent of visual field loss

• Suprathreshold

  • The intensity of the light at each location is pre determined at a level above threshold

  • Is the stimulus visible or not?

  • Screening

Supra threshold is for ______.

Screening

It takes half the time of a full threshold with SITA. True or False?

True

• SITA uses staircase procedure based on predictive probability (knowledge of normal age-related controls)

• Comes in 3 versions

  • SITA standard: 4-2 staircase (~7min); glaucoma diagnosis and monitoring progression

  • SITA fast: 6-3 staircase (less stimulus presentations needed, ~4min); tends to underestimate scotomas, also used for glaucoma monitoring

  • SITA faster: 6-3 staircase, no False Negative testing and no blind spot testing (~2min)

Sita standard 4-2 staircase is for glaucoma diagnosis and monitoring progression. True or False?

True

Automated Perimetry Advantages

• Reproducibility results

• Quantitative information

• Results in a more timely manner

• Experienced visual fields operator not require

• Earlier detection of defects

There are many more advantages to automated perimetry than manual. True or False?

True

Reliability Indicies:

• High Fixation loss 15% to 20% or more

• Acceptable False Positive 5-10%

• Acceptable 10-15% (patient not paying attention) False negative

False negatives increase when patients not paying attention. True or False?

True

A _________ can cause a generalised reduction in sensitivity.

Cataract

____________ value becomes more negative as field loss worsens.

Mean Deviation

____________ is useful in local loss progression and early glaucoma.

Pattern Standard DEviation (PSD)

______________ is similar to MD. 100% represents normal and it case be used as an indicator for progression.

Visual Field Index (VFI)

Glaucoma Hemifield Test:

• Indicator of the differences between the superior and inferior halves of the field

  • Hemifield

• Points on the field plots are clustered into 10 regions

• Mirror of clusters in the top and bottom hemifield

• Compared with the corresponding cluster in the opposite hemifield

• GHT outcomes

  • Outside normal limits

  • Borderline

  • General reduction in sensitivity

  • Abnormally high sensitivity

  • Within normal limits

• Outside normal limits

  • Matched pair difference only found in 1% of normal database

  • Two of matched pairs more abnormal than 99.5% of normal database

• Borderline

  • Matched pair difference found in 3% of normal database

• General reduction in sensitivity

  • Outside normal limits not met

  • Best region of plot depressed to level of 0.5% of normal database

• Abnormally high sensitivity

  • Region of plot is better than 99.5% of normal database

• Within normal limits

  • None of the above apply

This test compares the difference between the superior and inferior halves of hemifield. True or False?

True

The order to read a VF result sheet:

• .Px (Name, DOB, age, eye), date of test

• Strategy, stimulus

• Reliability

• Defect based on PD and TD plots

• Interpretation global indices

• DDx (what else could cause this defect)

• Additional tests

This is true or False?

True

Need to know:

• Kinetic vs static perimetry – stimulus moves vs stimulus stationary

• Suprathreshold tests are for screening – they test increments brighter (3, 4 or 6dB)

  • high specificity but low sensitivity (true defects detected, shallow defects may be missed)

  • Saves time

• Reliability of result judged on ..

  • Fixation loss <20%

  • False positive <10%

  • False negative <15%

• Lesions up to chiasm are unilateral (often around the horizontal midline, but not always)

• Lesions from chiasm up to occipital lobe show bilateral (i.e., VF of right and left eye) around the vertical midline

Fixation loss less than <20% is acceptable. True or False?

True