1. Andrew Miller Lead Optometrist Focus Birmingham
Acuity Measurement
Basic Visual Fields
Andrew Miller Lead Optometrist Focus Birmingham

2. Introduction A lot to fit in, apologies Morning Afternoon Acuity
Visual Fields Testing
Afternoon
Understanding Spectacle Prescriptions
Little About Low Vision Assessment

3. Distance Vision/Visual Acuity
Measures maximal spatial resolution
Tells us what people can see in the distance!
Core Measurement
Easy to take,
but many ways to do it...
6/60
20/200
1.00logMAR
0.1
Snellen
Decimal notation
logMAR

4. Snellen
In 1862 Dr Herman Snelling introduced a chart made of letters on a 5 x5 grid
“Normal vision” is defined as being able to resolve a letter of 5 minutes of arc at 6m distance.
Common usage

5. Snellen Snellen is represented by a fraction E.g. 6/6 6/24
The top number tells us the testing distance
The Bottom number tells us how much bigger (or further away)the letter was than the standard letter
Arithmetic Scale
So the 6/12 letter is twice as big as the 6/6
The 6/18 is half the size of the 6/36
3/60 is equivalent of 6/120

6. Snellen Around the World
Americans still use feet and inches
Therefore 6m becomes 20ft
6/6 becomes 20/20
Europeans commonly use a
decimal notation.
They simply convert the Snellen
fraction into a decimal
6/6 = 1.0
6/12 = 0.5
6/60 = 0.1

7. Snellen Pros Cons Quick Used a lot Reasonably well understood
Often what people quote even if they have measured acuity in a different way
Aimed at fully sighted people
Large Gaps at lower acuity bands
Too few letters at the top of the chart
Depressing for low vision patients
Uneven Crowding
Not reproducible?
How do I measure 6/48
What if acuity is less than 6/60?

8. logMAR and ETDRS Chart logMAR is what I use! Chart is logarithmic
Needs some mental arithmetic
Or a calculator!

9. logMAR and ETDRS Chart How does it work? Test at 4m
Every line has a value.
Top line is 1.00
Every line lower the value DECREASES by 0.1. Second row 0.9 Third row 0.8
If get every letter right you score the value for the line.

10. logMAR and ETDRS Chart
For every letter you get wrong you add 0.02 to the value of the line
e.g. if you read 2 letters wrong on the 0.90 line your logMAR value is
= 0.94logMAR
If you cannot read the chart at 4m you test at half the distance and add 0.30 to your score

11. logMAR Pro Con Linear Progression Even Gaps Even Crowding
Greater range of acuity levels
Better subjective measurement
Can calculate per letter
Much more accurate for determining low vision
Better for seeing if your interventions have worked
Patients feel happy they can read something
Letters even legibility
Needs more knowledge
People often don’t understand your result
Takes longer
Harder with kids?

12. Idiot’s Guide? Poor Acuity Good Acuity Snellen 6/60 6/6 Decimal 0.1
1.0
logMAR
1.00logMAR
0.00logMAR
Low Value
High Value
Snellen
GOOD
BAD
Decimal
logMAR

13. Does Acuity Tell Us Everything?
VA tells us a very specific piece of information and does not give the whole picture
Other Measurements We Should Be Aware of when assessing Visual Function
CSF
Visual Fields
Accommodation
Colour vision
Reading speed/acuity

14. Contrast Sensitivity Function Loss
CSF measures how well you see when contrast falls.
Optic Nerve lesion or lens opacity often leaves CSF reduced.
Causes
Difficulty reading packaging
Problems seeing kerbs
Problems seeing gradients

15. Contrast Sensitivity Function Loss
Various Ways of Measuring Contrast Sensitivity

16. CSF what can you do? CHANGE THE CONTRAST Use Higher Contrast
Contrasting Backgrounds
Paint Stair Edges
Bold Pens
Electronic enhancement
Improve Lighting
Magnification Not Helpful

17. Andrew Miller MSc MCOptom
Visual Fields
Andrew Miller MSc MCOptom

18. Introduction What are visual fields Methods of Field Testing
Fields and low vision assessments
What Does it Mean to the Patient
Action Points
Conclusions

19. Normal Visual Fields
The field of vision is defined as the area that is perceived simultaneously by a fixating eye. The limits of the normal field of vision are 60° into the superior field, 75° into the inferior field, 110° temporally, and 60° nasally.
Harry Moss Traquair ( ) "an island of vision or hill of vision surrounded by a sea of blindness".

20. Hill of Vision

21. Testing Visual Fields
Visual Fields assess the height and extent of the hill of vision
Different Methods
Static
Kinetic
Formal
Goldmann
Humphrey
Henson
Informal
Amsler
Confrontation
Observation

22. Static Testing Size and location of the test target remain constant.
The shape of the island is defined by repeating a threshold measurement at various locations in the field of vision
Retinal sensitivity at a specific location is determined by varying the brightness of the test target.
Either
Full Threshold (accurate/slower)
Supra Threshold (screening/quicker)

23. Static Testing- full threshold
JODY R. PILTZ-SEYMOUR, ONECA HEATH-PHILLIP and STEPHEN M. DRANCE

24. Results from Static Perimetry
Full Threshold

25. Static Testing- Supra threshold

26. Results from Static Perimetry
Supra Threshold

27. Kinetic Fields
Stimulus moved from a non-seeing area of the visual field to a seeing area along a set meridian.
Repeated along other meridians, usually spaced every 15°.
In kinetic perimetry, one attempts to find locations in the visual field of equal retinal sensitivity.
Lines joining points of equal sensitivity called isopter.
Change luminance and the size of the target is changed to plot other isopters.

29. Results From Kinetic Perimetry

30. Differences
In kinetic perimetry, the island of vision is approached horizontally. Isopters can be considered the contour lines on the hill of vision
Static approached vertically
Static automated more easily
Kinetic better with poorer acuity?

31. Informal Fields Testing
Confrontation Testing
Amsler Grid
Observation

32. Scottish Sensory Centre

33. Pros and Cons Pros Cons Easy Easy to get it wrong Simple Too Simple
Can be done at school
Not quantifiable

34. Fields and Low Vision I use the Esterman test
120 targets
Wide test arc (160 degrees horizontally)
Targets are bright
Test is done binocularly
Static Test
Pt. watches fixation light
Pt .press button when light seen
Gives a real world view of the pattern of greatest loss

36. Plot example

37. Symptoms of Field loss Assumption Reality “Black in centre of vision”
“Just turn your head more”
Reality
Simulation specs are poor
Fields Loss often not well self reported
Hard to Judge where field loss starts and finishes

38. FIELD LOSS You “don’t know what you can’t see” Sim Specs are not real
Life
Action
Counselling (orientation awareness)
Mobility Training

39. Loss of Fields : Symptoms and Case Study
82 year old man
Stroke 2 years ago.
Seen hospital “nothing could be done”
Stroke has given dad a problem with his left eye.
Son noticed dad very withdrawn since moving to a new residential home.
Staff saying he is only interested in the television and ignores people.

40. Field Plot

41. Field Plot

42. Field Loss Field loss causes the problems we suspect.
Tripping
Falling over
Fear
Isolation
But not necessarily the symptoms we expect