Assessing Functionality of Vision

Question 1

How do we define visual acuity?

Answer 1

A measure of the ability of the eye to distinguish shapes and the details of objects at a given distance.

Question 2

What VA do we expect in a newborn? 1mo old? 4-6mo old? 3yr old?

Answer 2

Newborn 6/240
1 month 6/180 – 6/90
4-6 months 6/18 – 6/6
3 years 6/6*
* Tested with single optotypes

Question 3

What did Leone et al. find about normative VA?

Answer 3

VA improves with age, most dramatically in the first 24 months of life, followed by a consistent phase of slower improvement continuing up to 72 months and likely beyond

Question 4

What did Pan et al. (2009) find about normative multi-ethnic monocular VA in children?

Answer 4

1722 African-American and Hispanic children aged 30 to 72 months. (2.5 - 6 yrs) - same as what Leone et al. found in Sydney

Question 5

When is someone registered with a certificate of Visual Impairment (CVI)?

Answer 5

• Severe sight impairment (Blind) – VA < 1.3 logMAR (3/60)
• Sight impairment (partially sighted) – VA 1.0 logMAR (6/60) or less dependent on visual fields

Question 6

What is a Functional Vision Assessment?

Answer 6

Functional vision refers to what a person can see and how an individual uses whatever vision he or she has in everyday life.

FVA often required in adults or children with special needs with multiple and complex disabilities and when conventional VA tests are not possible.

Question 7

What challenges are there with conventional VA testing?

Answer 7

• Crowded LogMAR tests not always possible in these patients . Especially at 3 m
• FCPL and Cardiff cards don’t always stimulate vision. Children may not be interested in these
• Clinician cannot easily relate findings of a visual acuity score to real life situations
• When its low levels of acuity scorings it is difficult to give parents / carers / teachers any useful information about the vision measured which they can use to assist the child’s learning.

Question 8

How might be simply assess vision in a ?”blind” infant/toddler?

Answer 8

• Swinging baby test
• Blink reflex
• Pupils
• Fix and follow
• Reactions to smiling/people in the room
• Diffuse light reaction (orientation to light as an indicator of minimal VA in very young infants and cases of suspected total blindness)
• Lateral tracking
• Peripheral refixation - lateral field
• Symmetrical corneal reflexes
• Convergence
• Attention at distance
• Defensive blink to approaching objects (dev of visuo-motor response related to distance perception)
• Optokinetic Nystagmus
• Acuity Cards
• Videorefraction
• Lang test
• Batting/reaching
• Pick up black and white cotton (contrast sensitivity)
• Retrieval of a totally, and then partially, covered object

Question 9

What battery of tests can we use in testing child development?

Answer 9

Atkinson et al. (2002)
A test battery of child development for examining functional vision (ABCDEFV)

A battery of 22 tests, intended to give an integrated assessment of children’s functional visual capacities between birth - 4 years of age

As well as sensory visual measures such as visual acuity, visual fields and stereopsis, the battery is intended to tap a range of perceptual, motor, spatial and cognitive aspects of visual function

Normative data are reported on nine age groups between 0–6 weeks and 31–36 months, each including 32–43 typically developing children
The study carried out all the tests and then suggested which ones would be more suitable for which age group.

Question 10

What is the Bradford Visual Function Box for?

Answer 10

Assessing Visual Acuity/Function in children with Special needs (Pilling, Outhwaite and Bruce, 2016)?

Question 11

What does the Bradford Visual Function Box (BVFB) comprise of? (Pilling, Outhwaite and Bruce, 2016)

Answer 11

(Pilling, Outhwaite and Bruce, 2016)

The box (BVFB) comprises a selection of items (small toys) of different size and colour, which are presented to the child and the response observed

The aim of this study was to establish its inter-test validity in children with severe learning disability

The visual function of 22 children with severe learning disability was assessed using the BVFB

BVFB is designed to assess visual function in children with severe learning difficulties

Question 12

What do you do if VA is <1.0 logMAR (6/60)?

Answer 12

• Reduced the test distance i.e. move the test closer
  Use LogMAR Crowded Test and bring the 0.8 (6/38) size letter closer i.e. 1.5m or as close as required for the patient to identify the letter
• Ask the patient if they can see the letters better by fixing eccentrically i.e. by not looking directly at the letter. You may notice the eye is not centred. The patient is not able to fix with their fovea
• Patient’s fixation may be wandering as they try to locate optimum vision i.e. wandering fixation
• May also adopt an abnormal head posture
• Counting fingers
• Hand movements
• Perception of light
• Presence of OKN
• Electro-diagnostic testing
• Optical coherence tomography (OCT)

Question 13

What is the Bailey and Lovie (2013) formulae for reducing VA testing distance?

Answer 13

“Visual Angle” and “Minimum Angle of Resolution” are similar terms and both express the angular size of the critical detail in minutes of arc (min-arc).

The logarithm of the Minimum Angle of Resolution (logMAR)

On the logMAR scale, a value of 0.0 corresponds to MAR=1.0 (6/6, 20/200)

LogMAR ratio is 1.2589
V = Visual acuity
M = size of the letter optotype
m = testing distance in metres
Formulae: 1/V = M*(1/m)