Functional visual acuity FVA Flashcards
Visual acuity
A measure of the ability of the eye to distinguish shapes and the details of objects at a given distance. It is assessed by determining the finest spacial detail that the visual system can discriminate.
Importance of consistency in VA
It is important to assess VA in a consistent way in order to detect any changes in vision.
How is VA assessed components
It is assessed by determining the finest spacial detail that the visual system can discriminate
Ø Ability to resolve a pattern into spatially separated elements
Ø Denotes the size of detail that can just be resolved by an individual = Visual resolution
Visual progress of newborn
6/240 VA
on single optotypes
Visual progress of 1 month old
6/180 – 6/90 VA
on single optotypes
Visual progress of 4-6 month old
6/18 – 6/6 VA
on single optotypes
Visual progress of 3 year old
6/6 VA
on single optotypes
Study- VA in children is Sydney in lecture slides
Findings- Normal population distribution of visual acuity by age group using monocular Teller Acuity Cards II.
Caucasian population
Vision screening 4-5 year olds
0.2 logmar
Normal population distribution of visual acuity by age group using monocular Teller Acuity Cards II.
Caucasian population
Study- ethnicity and monocular VA
-1722 African-American and Hispanic children aged 30 to 72 months.
Findings from African American and hispanic children study
There were significant differences in monocular visual acuity between African-American and Hispanic children within the specified age range.
Further analysis revealed potential disparities in visual acuity development and outcomes based on ethnicity.
The study suggests the need for tailored interventions or screenings to address any identified discrepancies in visual acuity among children from different ethnic backgrounds.
Visual acuity standards
Normative Paediatric VA is not as good as Adult VA
Vision screening referral criteria for children worse than 0.2 logMAR
Normative adult VA: 0.0 logMAR - many achieve better than this
Certificate of visual impairment
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
Functional vision assessment
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.
Challenges with conventional VA testing
Ø Crowded LogMAR tests not always possible in these patients . Especially at 3 m
Ø FCPL and Cardiff cards don’t always stimulate vision. Children may not be interested in these
Ø Clinician cannot easily relate findings of a visual acuity score to real life situations
Ø 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.
Study- A test battery of child development for examining functional vision ABCDEFV
components
A battery of 22 tests
Assessment of children’s functional visual capacities between birth - 4 years of age
Assesses:
sensory visual measures:
perceptual, motor, spatial and cognitive aspects of visual function
ABCDEFV test drawbacks
There are 22 tests- not functional because too many and child may have SEN needs and can’t focus for extended time
The Bradford visual function box
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
BVF test fixation targets
6 mm Red Bead
10 mm Green Bead
14 mm Stripy Bead
21 mm Fish Bead
28 mm Gold Bubble
40 mm Frog
65 mm Pink Spiky Ball
70 mm Pink Chicken
90 mm Fan
120mm Baby Shape Book
BVD test recording results
VA c/sgls BVFB
RE fix and follow 6mm red bead at 30cm
LE fix and follow 10mm green bead at 30cm
Reliabilty score RE- 3 LE- 3
Reliability score of BVF test
1= variable response—uncertain of result,
2= reasonable response—somewhat certain
of results
3= excellent response—very certain of result
Assessment proforma BVF test
- recognising mum/ family members, can find toy, tell if light or dark
-what toys do they enjoy playing with and what do they enjoy doing
-is there variability with their vision
-hearing concerns?
-hand movements possible
-head control possible- turn head to follow toy
-visual memory- look for dropped toy
Observations BVF test
Light perception- bright light in dark room, blink reflex
Facial perception- follow and look, return silent smile
Fixation
FCPL cards, black and white books 1-4
How long to hold fixation and visual attention
Repeatabilty BVF test-is it reliable when documenting visual function
Pillling et al (2016) showed good repeatability between two examiners.
When a difference was noted the reliability score was 1 (variable response)
Conclusion: The BVFB is a reliable tool to document visual function
Tip for BVF test
avoid noisy toys as this will give cues
Functional vision assessment in light and dark
Fixes pen torch
Follows pen torch horizontally
Follows pen torch vertically
Fixes large white light
Follows large white light horizontally
Follows large white light vertically
Reactions to changes in lighting
Daylight- Reacts to room lights being turned on/off
Darkened room- Reacts to room lights being turned on/off
Note
Toys and targets graded by size 1-5
Fix and follows horizontally and vertically
Pupil reactions AND blink
React to direct stimulation
Reacts to consensual light stimulation
Relative afferent pupillary defect RAPD
Description i.e. anisocoria
Blink reflex
Blinks to approaching silent object
FVA and OKN drum
can use OKN drum as this can assess optiokinetic nystagmus horizontally and vertically.
can do swinging baby/ dolls head movements and visual field to confrontation with toys
Forced choice preferential looking techniques FCPL
Square wave grating – black and white stripes of equal width
FCPL method
Keller Cards – test distance is 38cm
Ideal age – 8 weeks to 12 months
Present card and observe whether infant looks toward the grating – repeat with finer gratings
Staircase procedure
Vision is recorded in cycles/degree – also equivalences in logMAR & Snellen
FCPL techniques
Allows measurement of vision in infants and very young children
Delayed visual maturation – infants who appear blind when seen before 10-15 weeks
Early detection of gross amblyopia
Monitoring progress of children being treated for infantile cataracts and associated deprivation amblyopia
Patients with mental/ physical disability
Grating can…
overestimate vision when compared with conventional tests which assess recognition acuity
Minimal angle of resolution=
Resolving power of the eye minus smallest stimulus discernible
What do you do if VA is < 1.0 logMAR (6/60)?
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
Wandering fixation pts have poorer VA and AHP
If VA is less than 1/60 test options are..
counting fingers, hand movements, perception of light, presence of OKN and EDTs
Formula for reducing VA test distance
Formulae: 1/V = M*(1/m)
V = Visual acuity
M = size of the letter optotype
m = testing distance in metres
Oduntan (2006) A practical logMAR near reference table for low vision practitioners: design and applications. S Afr Optom. 65:157-162. and table in pp
LogMAR ratio is 1.2589
