Visual fields Flashcards
Why test visual fields:
*Incidence of VF loss in general population is 3-5%; increases with age
*VF loss can be sight /life threatening
*Normal VF may be diagnostically important
*Presence of a VF defect may be the only evidence of disease
*If px test results normal and VF normal = px malingering
*Can be life threatening – if got tumour that’s causing vision loss you test visual field because it could be life threatening – can be picked up on visual field test
What are the two types of methods of assessing visual fields:
1.Static
2.Kinetic
Kinetic perimetry
*Stimulus of fixed size or fixed illuminance
*Moving target moved from non seeing to seeing until px detects it
*Considered out-dated
*Intensity constant
*Bjerrum Screen/Goldmann Tonometry
Static perimetry
*Brightness increases or decreases
*More accurate
*Location of stimulus is constant, intensity increases/decreases
*Best technique for the detection and investigation of early field loss
*Detection of early field loss is crucial in detection of Primary Open Angle Glaucoma
What are the TWO types of threshold strategies:
-Full threshold
-SITA/ZATA
What is full threshold:
-Each location is thresholded using a staircase procedure
-The intensity at which a px can see is checked at each location
-So it involves measuring the precise threshold sensitivity by varying the stimulus intensity
Pros and cons of full threshold:
+ = accurate
-= takes long
What happens in suprathreshold strategies:
-Stimuli are first presented at an intensity that is calculated to be above the patient’s threshold.
-If the stimuli are seen, then it is assumed that no significant defect exists
-Stimuli within the scotoma i.e area of defect cannot be seen
-Single stimulus or multiple stimulus
What strategy does single stimulus and multiple stimulus come under:
Suprathreshold
What strategy does SITA/ZATA come under:
Full threshold
Single stimulus vs multiple stimulus:
*Single stimulus – present 1 light at time
*Multiple stimulus – present multiple lights at a time
Advantages of threshold strategies:
-Sensitive to shallow field loss and early fluctuations in glaucomatous VF loss
-Visual field progression (glaucoma)
-Allows statistical analysis
-Diagnostic information
-Provides information about the reliability of the data by comparing the measured visual field with a normal visual field
-Highly skilled perimetrist not needed
-Reproducible VF test/testing conditions
-Easier to monitor progression over time
Disadvantages of threshold strategies:
Time consuming although newer threshold procedures offer a comparable examination time
Advantages of suprathreshold strategies:
-Multiple stimuli or single stimulus suprathreshold strategies, allows perimetry to become of key importance to optometrists, because it speeds up the investigation, allowing visual fields to be assessed on every visit
-Good screening test
-No need for highly trained perimetrist
-Rapid examination of visual field
Advantages of suprathreshold strategies:
-Insensitivity to shallow field defects
-Shallow defects are the earliest in POAG
-Can miss defects if threshold is incorrectly estimated
What equipment is used in kinetic visual fields:
-Gross perimetry/Confrontation
-Arc perimeters
-Certain bowl perimeters
What equipment is used in static perimetry:
-Automated perimeters
-Automated/semi – automated perimeters
What is automated perimeters:
The decision-making process of the examination strategy is exclusively controlled by computer, and does not require the intervention of the operator
Examples of automated perimeters:
-Humphrey Field Analyser
-Modern Henson models
What is semi - automated perimeters:
Require the operator to control the examination strategy
Examples of semi - automated perimeters:
Some Henson models are semi-automated for suprathreshold testing
What visual field techniques are used in opticians:
-Gross perimetery/confrontation
-Suprathreshold static test of central field
-Multiple stimulus static perimetry E.G. Henson
-Single stimulus static perimetry E.G. HFA/Henson
When is SITA/ZATA Fast threshold strategy used instead of the suprathreshold test:
-If patient has symptoms or a family history of glaucoma
-Or FH of glaucoma
What is the purpose of gross perimetry/ confrontation testing:
-Carried out routinely as part of a screening process
-May identify those patients who would benefit from a more detailed investigation of their peripheral fields
What can you use if further investigation is required for gross perimetry/ confrontation testing:
-Kinetic methods on a bowl perimeter
-Peripheral static methods on a HFA (or similar
Disadvantage of gross perimetry/ confrontation testing:
Sensitivity of test is low
Which visual field tests are binocular:
Estermann test
Which field test would you do on px’s:
-Suprathreshold
-SITA Fast
When would you wear rx glasses for central static fields:
-A prescription appropriate for the radius of the bowl (or distance from the screen) must be worn
-Because refractive blur affects central field
-Typical bowl radius is 30cm (HVFA 2) or 25cm (Henson 6000 & 8000)
Which add on top of distance correction will you use for visual fields:
40-44 = +1.50
45-49 = +2.00
50-54 = +2.50
55-59 = +3.00
60-64 = +3.50
>64 = +4.00
Static perimetry: key point to remember:
- Each patient must be appropriately corrected for the test distance
-Use full aperture lenses or single vision reading glasses whenever possible
-For astigmatism equal to or greater than 1D, best to use full cylindrical power
-For very high Rx (greater than 8D) it is best to use CL if available and appropriate
-If pupil dilated, assume full cycloplegia and use full add for test distance.
-Bifocals and progressives should be used only as a last resort
-Tinted lenses in glasses should not be worn if there is any acceptable alternative
-No correction may be best for some patients e.g. some low myopes
Why shouldn’t you use tinted or half aperture lenses for visual fields:
-Using half aperture lenses will create visual field defect
-Tinted lenses shouldn’t be worn cause will effect pxs sensitivity and brightness of light they can see
What are the three levels of investigation available for Henson suprathreshold tests:
1.26 retinal locations in 8 patterns
*Designed for screening
2.68 retinal locations in 20 patterns
*Designed for patients where a field defect is suspected or there are other reasons for performing a more rigorous test
*This is the approach recommended for screening in PCC with Henson
3.136 retinal locations in 40 patterns
*Designed to establish the extent of a defect
Types of supra threshold:
*Single stimulus central field = automatically
*Multiple stimulus central field = done by optom
How important is px position:
- If px not properly set up, can cause VF defect or wrong results
What do you do to make sure px can see all 4 dots:
Press that plus button
Single stimulus vs multiple stimulus:
*In the single stimulus suprathreshold strategy the threshold setting is done automatically
*In the multiple stimulus supra-threshold strategy the threshold setting is done semi- automatically with the perimetrist input
What is important in supra threshold testing:
*DON’T DO MEASURE BY AGE – that means you are suggesting everyone at 60 has same threshold etc using fixed threshold – everyones threshold is different – effected by presence or absence of lens opacities
*SO DO THRESHOLD BY MEASURE – more accurate
What are the approaches for suprathreshold strategies on Humphreys field analyser:
1.Threshold related:
*An “expected hill of vision” is calculated, and stimulus intensity set 6 dB brighter than expected at each location – e.g. C-76 point test (takes about 2 mins/eye)
2.Three-zone
*The expected hill of vision is calculated as in 1, and defects classified as relative or absolute
3.Quantify defect strategy
*Locations missed twice at screening level are thresholded
*Clinic recommendation is usually the C-76 quantify defect program as standard for screening in clinics
4.Age reference strategy
*The expected hill of vision is estimated from the patient’s birth date
*40 point screening test takes only 1.5 minutes per eye
How is depth of scotoma assessed if suprathreshold stimuli are missed:
By establishing the threshold
*Measuring how deep defect is
*Points in red not seen by px
*Is presenting at a brighter threshold until px sees it = green
*So its trying to quantify depth of defect
Estermann visual field test:
*Binocular
*Used for assessing if fit to drive
*No trial lenses needed
*If requires glasses to function daily then wear them
What visual field to use and when:
*If you want to screen the visual field : use supra-threshold strategies: Henson single or multiple stimulus (extended to 68 points) or C40/76 on HVF
*If speed is important, your patient is ‘young’ and probably has ‘normal’ VFs use :multiple stimulus supra-threshold strategy on Henson. Also use it on ‘older’ people as they sometimes prefer examiner interaction.
*If your patient has a known defect then the single stimulus strategies are better. HVF Sita Fast 24-2 or Henson ZATA Fast 24-2
*If you wish to quantify the extent of loss with the indices mean defect, loss variance and fluctuation, then use the full or ZATA/SITA threshold strategies.
*If you wish to measure accurately the depth of a defect then use the full threshold strategy- this is rarely done in PCC
What field tests should I do if the patient has symptoms or has a family history of glaucoma?
*Gross perimetry
*Central suprathreshold or SITA Fast 24-2
When would you use amsler chart:
if you see a suspicious macula, or if you are unable to see the macula
What distance is amsler chart:
Designed to be used at 28 - 32 cm = the patient should be corrected for this distance
Questions for amsler chart:
*Ask px to look at dot in middle
*Look at 4 corners of square
*Look at 4 sides of square
*Look at all lines horizontal and vertical
*Are any distorted or missing
