Visual Fields - Clinical Flashcards
what is the clinical visual field?
all the space an eye can see at a given time
what field does light hit coming from
-the nasal field
-the inferior field
-temporal field
-superior field
what causes the blindspot on every visual field?
the optic nerve but as a result of binocular vision we are not aware of it
what does the hill of vision demonstrate?
how the sensitivity of the eye to light varies
how can you see a visual defect using hill of vision and give an example of what can cause this
a visual defect is shown by any change from the normal topography of the hill of vision. cataract can cause this
what are the two types of perimetry visual fields?
kinetic and static
what is the most common form of kinetic perimetry compared to what?
goldmann which is where the target is moved manually compared to octopus where the target is automated
what are the advatanges of kinetic perimetry?
-not confined to testing algorithms
-can be used on people who cant use a visual field machine
what are the limitations of kinetic perimetry?
-needs an experienced practitioner
-Spatial summation of receptive fields results in us being able to see a moving target in the periphery better than a static one
* This means we could miss a damaged area if areas around it are healthy
* Results are dependent on the patient’s reaction time
* We could record the field as being worse than it is
what are the two features of automated static perimetry?
-light stimuli are fixed in position within the visual field
-the size of the light stays the same but brightness is varied
what are the two types of automated static perimetry?
-suprathreshold
-full threshold
what are the advantages of automated static perimetry?
-standardised
-highly repeatable
-not reliant on practitioner experience
-quicker than kinetic perimetry
what are the disadvantages of automated static perimetry?
-tests pre determined points
-doesn’t test full temporal field
what does threshold do? how is it determined using the 4-2db algorithm?
-determines sensitivity individually for each tested location and offers a detailed view of a patients vision but can be time - consuming.
-determined by the maximum light energy required to elicit a visual response with a 50% detection probability
what is SITA
A full threshold static visual field test designed to be quicker than 4-2db so 2 mins compared to 15 mins
what are the advantages of threshold perimetry?
-maps hill vision with greater precision
-measured thresholds are compared to an age-matched normal
what are the limitations of threshold perimetry?
-can take a long time compared to suprathreshold
what are fixation losses on visual fields?
where the machine calculates where the blindspot by shining a light in this area and if the patient responds they are not focussing correctly
what causes false positive errors?
the patient has pressed the button when no light has been presented
what causes false negatives?
when a very bright light is shone in an area the patient has already responded to which suggests patient is not responding to all the stimuli they can see
what can high false negatives suggest?
the patient does have a visual defect
what does gross visual field testing do?
describes using a handheld target to detect visual field defects so the larger the target the less sensitive the area
how does the amsler grid work?
assess the the health of the macula region, pathology presence means patient may report missing squares or lines may look distorted
what is the esterman field test?
a binocular visual field test that is used by DVLA to judge whether a patient’s visual field is full enough to drive
