1. Low Vision Evaluation
Ms MB JAN- 24/01/2012

2. Content The difference between a low vision exam and a regular exam
The Case History
Evaluating visual performance

3. 4. Evaluating visual performance
Visual acuity
Visual field evaluation
Contrast sensitivity
Colour vision
5. Objective refraction
6. Subjective refraction
7. Ocular health evaluation

4. OUTCOMES
At the end of this lecture, learners should be able to:

5. Discuss the importance of a case history specifically for a low vision patient
Discuss specific questions that will be asked to a low vision patient
Describe the different techniques and charts used to measure a low vision VA (near, distance, aided, unaided etc.)

6. Discuss the need for evaluating visual fields in a LV patient
Discuss methods and techniques for evaluating visual fields in a LV patient
Discuss the need for evaluating contrast sensitivity in a LV patient

7. Discuss the need for evaluating colour vision in a LV patient
Discuss the methods and techniques used for evaluating colour vision in a LV patient
Discuss the objective refraction techniques available to the low vision optometrist
Discuss the technique and implications of radical retinoscopy

8. Discuss the method used for refracting a low vision patient
Analyze a low vision case based on a history, and then decide on and describe the most appropriate evaluation routine for a specific patient
Distinguish between a low vision refraction routine and a normal refraction routine
Explain the concept of JND (just noticeable difference) and be able to use it to test a low vision patient

9. The pre-evaluation information sheet
It sets clear boundaries on what you will be able to do
Draw up your own sheet in practice

10. Information sheet The appointment duration
Schedule appointment around a time when patient’s vision is stable
Bring with old glasses, magnifiers – even if not usable anymore

11. Think about specific problems the patient is experiencing
Start thinking in terms of goals – write down what you would like to achieve

12. Bring along special materials he/she want to be able to use (E. g
Bring along special materials he/she want to be able to use (E.g. books)
Bring along a report from the ophthalmologist

13. Follow-up visits or training sessions with equipment may be necessary
State that there are no miracles, we will use your remaining vision effectively

14. The difference between a low vision examination and a regular exam
Give the differences and explain each point given

15. Disadvantages of using phoropter
Why not phoropter?

16. NB. Very important, It has to be even more detailed
Case History
NB. Very important, It has to be even more detailed

17. The patient interview
The successful patient interview has 3 functions (Cohen-Cole)
Gathering data to learn about the patient’s problem
Developing rapport, and responding to the patient’s emotions
Educating patients about their problems, and motivating them to adhere to the prescribed treatment

18. Interview techniques
Both parties should be seated at eye-to- eye height
Seating should be comfortable
Control lighting – not too dim or bright
Carefully observe the patient

19. Use both open-ended and specific questions
May be emotionally charged
Note taking should be done subtly

20. Be alert to inconsistencies
Take sufficient time that patient doesn’t feel rushed
BUT keep it brief – old people tire more easily
Use positive language
Question in a friendly, enthusiastic manner

21. Adjust pace to that of patient.
Don’t use medical jargon, explain patient’s condition if they do not understand it
Never give false reassurances
Primary aim is to help patient – don’t fear to be inquisitive – but respect privacy too!

22. The purpose of the case history
Why is it important to take LV case history?

23. The real questions you want answered are:
What does the patient want?
What does the patient need?
What is the real reason for the patient’s visit?

24. Information required Basic identifying information
Name, address etc
Who accompanied the patient?
Support system / self-sufficient?
Relative, friend, counselor, teacher etc
Contact person
Provide insight into history

25. Diagnosis of eye condition
Referral source
Send thank you note
Reports
Diagnosis of eye condition
In patient’s own words
See if patient understands condition
Begin with patient education on problems.

26. Visual history
Duration
Previous care
Nature of vision loss (congenital or acquired? Stable or progressive?)
Fluctuation of vision

27. Problems with color vision Is there a preferred eye?
Problem with glare or lighting?
Current glasses / low vision aid
Current visual capability (specific task-related questions)
Smallest print read?
Newsprint
Headlines
Large print

28. Family visual history Able to watch television? What viewing distance?
Size screen?
Can you recognize faces at a distance?
Can you see well enough to get around?
Family visual history

29. 5. Medical history
Undergoing treatment for medical condition?
Does the patient have a disease with known ocular implications?
Is there medical problems that might affect the use of a LVA? (stroke)
Family history
Allergies and drug sensitivities
Medications (many systemic drugs have ocular side-effects)

30. 6. Employment or school history
Investigate the effect the visual loss has on the work/school performance
Investigate the use of appropriate devices to alleviate problems
Some older people might want to continue their education
Avocations
Hobbies or activities

31. 8. Social assessment Does the patient live alone or with family?
How is daily life affected by the vision problem?
Does the patient have a support network?
Is the patient’s independence threatened?

32. 10. General appearance of patient
Well groomed, clean or untidy?
Food stains – cannot see that level of detail
Poor grooming - emotional disorders such as depression
Walk without assistance?
Mobility
Does the patient look ill?

33. Patient goals (Chief complaint)
Possibly the most important part of the case history
Allow a full elaboration of the visual disabilities
Patient’s new problem should be fully investigated

34. After the patient has completed a list of complaints, several issues should be addressed regardless of the patient’s failure to mention them
Distance vision
Near vision
Orientation and mobility skills
Glare
Lifestyle

35. External evaluation
Some do this just after VA’s, but depends on circumstances. Give an example
Brief look into the eyes, do not shine bright lights into the eye

36. Note the following about the eyes:
Position of eyes (strabismus)
Pupil – size, reaction to light, appearance,
Cornea – opacities: size, density, position
Lens – opacities, position (especially IOL)
Motility – strabismus, nystagmus, restrictions
Binocular dysfunction is usually of secondary importance

37. Evaluating visual performance

38. Why?
Compare with normal performance, or accepted standard (eg driving regulations)
Set a baseline for monitoring the condition
Quantify the patient’s own subjective impression of visual performance

39. Early detection and diagnosis of (other) visual disorders
Assessment of the benefits of an intervention (medical, surgical, rehabilitation) program
Predicting visual function in every day tasks

40. Visual acuity

41. Visual acuity
1.Why do we want to accurately measure acuity? 2. Limitations of VA measurement 3. Factors affecting VA measurements 4. Distance Visual Acuity 5. Near Visual Acuity

42. Why do we want to accurately measure acuity?
It establishes a baseline from which to monitor pathology
Used to predict the magnification level of the optical devices that will be required to achieve the patient’s goals
Often requested by other agencies to establish legal blindness, driving privileges, job eligibility etc.

43. Limitations of VA measurement
The clinical acuity does not give an accurate indication of the functional acuity. Explain
Clinical measure of person’s ability to read letters under controlled circumstances
It doesn’t always correlate with daily activities

44. Function can be influenced by differences in contrast sensitivity, glare sensitivity, motivation and numerous other factors
VA can vary due to test setting, illumination, doctor-patient relationship and target contrast

45. Factors affecting VA measurements

46. How does each of the following factors affect VA measurement?
Lighting
Optotype
Mental state of the patient
Instructions to patient/attitude / encouragement
Glare recovery
Educational level
Recognition/memory/speech
Motivation

47. Distance Visual Acuity
VA Notations
Acuity chart design
Currently used charts
Measuring distance VA

48. VA Notations
Snellen
Either metric or imperial
We use imperial (feet)
LogMar (logarithm of the minimum angle of resolution)
Decimal: Snellen fraction
Angular (specified in minutes of arc)
Not used clinically

49. Acuity chart design
The following aspects of chart design can be considered
Optotype –
style of print and selection of letters
Should yield equivalent results to Landolt C
Number of letters per row
Equivalent – equal task progression
5 good clinically

50. Sequence of Letters Optotype Size Letter spacing
not form words/part of words
Optotype Size
0.1 logarithmic progression of character size
Accurate measurements at both standard and non-standard test distance
Letter spacing
systematic

51. Commonly used charts Feinbloom Number Chart
Refer to your notes for advantages and disadvantages
Of this chart

52. Bailey-Lovie Advantages logMar format
Equal number of letters at each line
Can be used at any test distance

53. Projected cards
Other
Lighthouse distance acuity card (available in our clinic)
Lighthouse symbol cards
Designs for vision pediatric picture chart
University of Waterloo Chart
ETDRS chart

54. Measuring Visual Acuity
Use special low vision charts
Use a 10feet / 3 m working distance, or less
Emphasize residual vision
Offer encouragement and realistic feedback

55. Watch for and encourage eccentric viewing
Let the patient attempt to read all letters on the chart, and look for scotomas
Record as Snellen fraction, e.g 10/700
To convert between feet and meter, divide by (feet to meter) or multiply by 0.3 (meter to feet)
Always measure the acuity correctly: “less than 6/60” is unacceptable

56. Recording VA Measurements
Can have a measurement recorded as BEO (both eyes open) – distinguish from OU
Record the fractions read:
10/ of 10/ of 10 / 180

57. If the patient is unable to identify any optotypes, which designations are you going to use?

58. Near VA
The measurement of Near VA is a very important part of low vision
Most low vision patients struggle with reading, so magnification for near tasks is vital.

59. Near VA Specification of Nearpoint acuity
Measuring near acuity with the M system

60. Specification of Nearpoint acuity

61. M notation Method of choice Metric notation
Represents the distance in meters at which the target subtends an angle of 5’ of arc
1.00M subtends 5’ at 1m
Consistent, meaningful, flexible testing distance

62. N notation Point size of lower case Time Roman print
Standardized so that each point is 0.18 mm on the printed page
N10 is twice N5
Quite valid
Necessary to specify both test distance and target size

63. Point type Reduced Snellen
Actual print size in printers point notation
Size of slug, but not actual print size
Not a very good system
Reduced Snellen
Characters subtend the same angle indicated by the designated fraction at 20 feet
Specified test distance
Not 20 units, not a standard angle at 20 distance units
Cannot be used at any other distance
Useless - inflexible

64. Visual field evaluation
This another important aspect in low vision patient
Desirable to test all patient’s fields, but not always possible or practical

65. Instruments and techniques
Confrontation test
Only a gross estimate of the peripheral field
Screening method
Use light as a target

66. 2. Amsler grid

67. What is it? What does it look like?
Hand-held chart used to evaluate central 20° of vision
Can identify early changes like metamorphopsia or small central scotoma
What does it look like?
20 blocks x 0.5mm each

68. How does it work?
“Place a finely quared chart before an eye suffering from an affection of the central region of the retina, and the patient will immediately point out spots and distortions which affect his/her vision”
Measures the central 20° of vision if the chart is held 28-30cms from the eye

69. Types of charts Standard chart * Diagonal lines*
Every case, and usually sufficient
Diagonal lines*
Use with central scotoma
Red on black standard chart
Colour scotoma
Spots only
Reveals scotoma (no lines to be distorted)

70. Parallel lines for reading Standard block with smaller reading area
Use horizontally and vertically
Shows metamorphopsia
Parallel lines for reading
Allows a more minute evaluation of reading area
Standard block with smaller reading area
Minute examination of juxta-central area
Rectangle shows limit of fovea

71. General method Testing distance Optimal refraction
Clean, clear, well-lit chart
No ophthalmoscopy etc prior to evaluation
Do monocularly and then BEO to check for interference/suppression

72. Do monocularly and then BEO to check for interference/suppression
What chart?
Start with grid
Then use lines and spots
Do monocularly and then BEO to check for interference/suppression

73. Questions asked
Do you see the white spot in the centre of the squared chart?
4 corners? 4 sides? Whole of the square?
Network intact?
Lines straight + parallel?
Anything else?
Plotting the distortions?

74. Colour vision
Pathological conditions like glaucoma and ARMD can cause changes in colour vision, so it is necessary to evaluate this.
City University (not available in our clinic )
Isihara
Farnsworth D15

75. Isihara Tests for colour deficiency of congenital origin
Limited value in LV

76. Farnsworth D15
Available in our clinic
Check functional tests notes

79. Refraction
Always obtain the best possible refraction with the best possible VA – to give the lowest magnification, why?

80. Objective refraction Autorefractors Previous glasses
Limited use, due to media problems or eccentric viewing (off axis fixation)
Previous glasses
Can be a good starting point
Just make sure patient is using own Rx!
Patient might have had ocular surgery since glasses were prescribed

81. Keratometry Retinoscopy
Useful with astigmatism – amount and orientation of cyl
Patient may have difficulty fixating
Can be helpful in detecting irregular corneal surfaces or irregular astigmatism
Retinoscopy
Very useful, especially if patient is a poor responder
May be necessary to use radical retinoscopy

82. Retinoscopy Always do the ret in a trial frame
If there is no initial response or no reflex is seen, try using very large lens changes like +/- 5D, +/- 10D, +/- 20D

83. Radical retinoscopy
Radical retinoscopy means that the working distance is drastically reduced (as close as 10cm)
Radical retinoscopy can also mean deliberate off-axis scoping to use any visible reflex – this will induce unwanted cylinder, but the results can be potentially valuable

84. Subjective refraction
1 General conditions 2 The trial frame 3 The JND (just noticeable difference) 4 Spherical refraction 5 Cylindrical refraction

85. General conditions Use a 10feet or less working distance
Use full illumination unless otherwise indicated (e.g. patient with achromatopsia)
Use the low vision chart in subjective refraction
Always do a trial frame refraction

86. The trial frame
Why do we use it?

87. The refraction itself
Use standard methods and background knowledge to refine cylinder axis, power and sphere power

88. The JND (just noticeable difference)
Essential concept
The smallest dioptric step that a patient is able to discriminate
It is senseless and frustrating to use 0.25D steps when (because of the visual impairment) the patient can only notice a 1.00D change
Use the 10-feet equivalent as a rough starting point for JND

89. If the best VA is 10/100, the JND will be 1.00D
10/50 = JND of 0.50D

90. Spherical refraction
Use the tentative result from your objective refraction as a starting point
Determine the JND-lens, and check the sphere value with that
“Better with the lens, or without it”, not “one or two”
Patients may have a poor, slow, variable response – could be due to pathology

91. Cylindrical refraction
Check the axis using a hand-held Jackson Cross-cylinder of +/- 0.50D or +/- 1.00D if possible
You can also use rotation to blur/clear and let the patient rotate the axis her/himself

92. Cylinder power is checked in the normal way
Double check cyl power with direct comparison (with or without) – if no subjective or objective improvement, it is not necessary to prescribe
Finally, double check the spherical component again – use bracketing (eg and should blur equally)

93. Ocular health evaluation
OPTIONS:
Ophthalmoscopy
Keratometry
Tonometry
Slitlamp
Von Herick
Dilated fundus exam
Binocular indirect ophthalmoscopy