Visual field testing Flashcards
What is Traquair’s analogy about the visual field?
the VF is an island of vision surrounded by a sea of darkness
What is a real-life analogy of the visual field?
three-dimensional hill, the peak of the hill being the fovea
To what degrees does the visual field extend in all directions?
superiorly: 50 degrees
nasally: 60 degrees
inferiorly: 70 degrees
temporally: 90 degrees
What are the indications for visual field testing?
aids diagnosis and monitors certain ophthalmic (e.g. glaucoma) and neurological disease
What are the indications for visual field testing?
aids diagnosis and monitors certain ophthalmic (e.g. glaucoma) and neurological disease
What is an absolute vs relative scotoma?
- absolute = total loss of vision where no light can be perceived
- relative = area of partial visual loss where bright lights or larger targets are seen, whereas smaller and dimmer ones cannot be seen
What is an absolute vs relative scotoma?
- absolute = total loss of vision where no light can be perceived
- relative = area of partial visual loss where bright lights or larger targets are seen, whereas smaller and dimmer ones cannot be seen
What is meant by congruousness with regards to visual fields?
describes the degree to which the field defects match between the two eyes. more congruous = more posterior along visual pathway the lesion is located
What is meant by isopter?
a threshold line joining points of equal sensitivity on a VF chart
What is a key factor that can cause interpretation problems of all VFs?
refractive status
By how much can refractive status influence interpretation problems with VFs?
overcorrection by 1D will cause a reduction in sensitivity of 3.6dB
What are 4 things which must be standardised in order to properly compare serial VFs?
- background luminance
- stimulus size
- intensity
- exposure times
What are 4 times of VF assessments?
- confrontational VFs
- Amsler grid
- Kinetic perimetry
- Static perimetry
What are 2 examples of kinetic perimetry?
- Tangent screen (Bjerrum screen)
- Goldmann perimetry
What is a key type of static perimetry?
Humphrey perimetry
What is a key type of static perimetry?
Humphrey perimetry
What can be used for confrontation VFs to detect subtle defects?
hat pins (white and red)
Which part of the visual field is assessed by the Amsler grid?
central 10 degrees of the visual field
What are 2 advantages of the Amsler grid?
- easy to perform
- portable
What is the Amsler grid used to test for?
used to detect central and paracentral scotomas
At what distance is the Amsler grid held?
33cm
How much does each square on the Amsler grid subtend?
1 degree of VF
What is the overarching principal of kinetic perimetry?
- presents a moving stimulus of known luminance from a non-seeing area to a seeing area
- the target is then presented at various points around the clock and marked when recognised
- points are then joined, producing a line of equal threshold sensitivity which is named the isopter
What is another name for the Tangent screen and how frequently is itused in clinical practice?
Bjerrum screen - not commonly used
What part of the VF is examined by the Tangent screen?
central 30 degrees of VF
At what distance is the Tangent screen performed?
usually 2m (although 1m chart also available)
What is the method for performing Tangent screen kinetic perimetry?
- patient sits at 2m (2000mm) away from the screen and wears corrective lens for distance, if required
- the non-tested eye is occluded in turn
- patient fixates at a central spot and informs the operator when they see the targets
- white (w) or red (r) disc targets are used, either 1 or 2mm in diameter
How are the results of the Tangent screen kinetic perimetry processed?
- results plotted on charts at the patient sees them
- target size and colour are the numerator (1w, 2w, 1r or 2r) and the denominator is the distance (mm) of the patient from the chart (e.g. 1r/2000)
What is the commonest type of kinetic perimetry in clinical practice?
Goldmann perimetry
What is the commonest type of kinetic perimetry in clinical practice?
Goldmann perimetry
What is the name of the automated Goldmann machine in use?
Haag-Streit
What is most automated perimetry based on?
static on-off stimuli of variable luminance presented throughout the potential field
