Visual fields

Question 1

Why test visual fields:

Answer 1

*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

Question 2

What are the two types of methods of assessing visual fields:

Answer 2

1.Static
2.Kinetic

Question 3

Kinetic perimetry

Answer 3

*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

Question 4

Static perimetry

Answer 4

*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

Question 5

What are the TWO types of threshold strategies:

Answer 5

-Full threshold
-SITA/ZATA

Question 6

What is full threshold:

Answer 6

-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

Question 7

Pros and cons of full threshold:

Answer 7

+ = accurate
-= takes long

Question 8

What happens in suprathreshold strategies:

Answer 8

-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

Question 9

What strategy does single stimulus and multiple stimulus come under:

Answer 9

Suprathreshold

Question 10

What strategy does SITA/ZATA come under:

Answer 10

Full threshold

Question 11

Single stimulus vs multiple stimulus:

Answer 11

*Single stimulus – present 1 light at time
*Multiple stimulus – present multiple lights at a time

Question 12

Advantages of threshold strategies:

Answer 12

-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

Question 13

Disadvantages of threshold strategies:

Answer 13

Time consuming although newer threshold procedures offer a comparable examination time

Question 14

Advantages of suprathreshold strategies:

Answer 14

-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

Question 15

Advantages of suprathreshold strategies:

Answer 15

-Insensitivity to shallow field defects
-Shallow defects are the earliest in POAG
-Can miss defects if threshold is incorrectly estimated

Question 16

What equipment is used in kinetic visual fields:

Answer 16

-Gross perimetry/Confrontation
-Arc perimeters
-Certain bowl perimeters

Question 17

What equipment is used in static perimetry:

Answer 17

-Automated perimeters
-Automated/semi – automated perimeters

Question 18

What is automated perimeters:

Answer 18

The decision-making process of the examination strategy is exclusively controlled by computer, and does not require the intervention of the operator

Question 19

Examples of automated perimeters:

Answer 19

-Humphrey Field Analyser
-Modern Henson models

Question 20

What is semi - automated perimeters:

Answer 20

Require the operator to control the examination strategy

Question 21

Examples of semi - automated perimeters:

Answer 21

Some Henson models are semi-automated for suprathreshold testing

Question 22

What visual field techniques are used in opticians:

Answer 22

-Gross perimetery/confrontation
-Suprathreshold static test of central field
-Multiple stimulus static perimetry E.G. Henson
-Single stimulus static perimetry E.G. HFA/Henson

Question 23

When is SITA/ZATA Fast threshold strategy used instead of the suprathreshold test:

Answer 23

-If patient has symptoms or a family history of glaucoma
-Or FH of glaucoma

Question 24

What is the purpose of gross perimetry/ confrontation testing:

Answer 24

-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

Question 25

What can you use if further investigation is required for gross perimetry/ confrontation testing:

Answer 25

-Kinetic methods on a bowl perimeter
-Peripheral static methods on a HFA (or similar

Question 26

Disadvantage of gross perimetry/ confrontation testing:

Answer 26

Sensitivity of test is low

Question 27

Which visual field tests are binocular:

Answer 27

Estermann test

Question 28

Which field test would you do on px’s:

Answer 28

-Suprathreshold
-SITA Fast

Question 29

When would you wear rx glasses for central static fields:

Answer 29

-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)

Question 30

Which add on top of distance correction will you use for visual fields:

Answer 30

40-44 = +1.50
45-49 = +2.00
50-54 = +2.50
55-59 = +3.00
60-64 = +3.50
>64 = +4.00

Question 31

Static perimetry: key point to remember:

Answer 31

• 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

Question 32

Why shouldn’t you use tinted or half aperture lenses for visual fields:

Answer 32

-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

Question 33

What are the three levels of investigation available for Henson suprathreshold tests:

Answer 33

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

Question 34

Types of supra threshold:

Answer 34

*Single stimulus central field = automatically
*Multiple stimulus central field = done by optom

Question 35

How important is px position:

Answer 35

• If px not properly set up, can cause VF defect or wrong results

Question 36

What do you do to make sure px can see all 4 dots:

Answer 36

Press that plus button

Question 37

Single stimulus vs multiple stimulus:

Answer 37

*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

Question 38

What is important in supra threshold testing:

Answer 38

*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

Question 39

What are the approaches for suprathreshold strategies on Humphreys field analyser:

Answer 39

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

Question 40

How is depth of scotoma assessed if suprathreshold stimuli are missed:

Answer 40

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

Question 41

Estermann visual field test:

Answer 41

*Binocular
*Used for assessing if fit to drive
*No trial lenses needed
*If requires glasses to function daily then wear them

Question 42

What visual field to use and when:

Answer 42

*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

Question 43

What field tests should I do if the patient has symptoms or has a family history of glaucoma?

Answer 43

*Gross perimetry
*Central suprathreshold or SITA Fast 24-2

Question 44

When would you use amsler chart:

Answer 44

if you see a suspicious macula, or if you are unable to see the macula

Question 45

What distance is amsler chart:

Answer 45

Designed to be used at 28 - 32 cm = the patient should be corrected for this distance

Question 46

Questions for amsler chart:

Answer 46

*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