w4 measurement and development of vision Flashcards
(16 cards)
what do infants see at birth??
acuity at birth is about 6/300
this improves rapidly over the first 6-8 months of age
why is is imp to know what infants see??
medical/optometrical implications like the critical period and amblyopia
to further understand how the visual system works
screening??
child vision screening aims to identify children with reduced vision, effective early treatment can be offered such as glasses or patching which can help each child to reach their full social and educational potential
what is a critical period??
A time during early life when the anatomy and physiology of the visual system are particularly mutable or plastic
visual deprivation during this time may cause amblyopia (lazy eye)
strabismus
where the eyes dont point the same way due to muscle imbalance
when is the critical period??
From birth up to about 2 years, but some plasticity continues until 7–8 years old.
what happens if there is failure to provide appropriate visual stimulation during these critical periods??
can lead to long-term visual deficits, the most common of which is amblyopia.
what are common modifications to visual input that can reduce vision in infants??
optical errors - can lead to refractive amblyopia
eye muscle errors - can lead to strabismic amblyopia
light deprivation - can lead to deprivation amblyopia
ptosis - lid droop
Why is early detection of visual issues critical in infants?
due to the earlier in the intervention the better the chance of normal visual development due to neural plasticity
What are the main methods of assessing infant vision?
Preferential looking (PL): Teller/Keeler cards (behavioural measure)
Visual evoked responses/potentials ( VEP’s) (electrophysiological measure)
Optokinetic nystagmus (OKN)
Fixation and Following (tracking objects)
Response to light, observation of reflexes e.g. red reflex, pupil response
What is preferential looking and how does it work?
Infants generally prefer to view more complex or colourful stimuli than plain background stimuli
a method where infants are shown stripes vs. grey (plain bg vs pattern stimulus) if they look at the stripes, they can see them → gives estimate of grating acuity.
How does VEP help in assessing infant vision?
Electrical activity can be used as an objective measure of functioning at different levels of the
visual system like the visual evoked
potential (VEP). Measures electrical responses in the visual cortex to visual stimuli — gives objective data about acuity and neurological visual function.
advantages of VEPs
provide an objective measure of visual function eliminating the need for subjective responses from infants who cannot communicate verbally,
VEPs are useful for detecting visual impairments and developmental abnormalities in infants as young as a few months old allowing early intervention and treatment
disadvantages of VEPs
VEPs require infants to remain still during the test which can be challenging and determining the exact locations of the cortical responses in the brain can be diff w VEP measures as electrical current flow may be distorted by brain tissue and the skull
VEPs provide insight into teh overall function of the visual systgem but not the precise brain region localisation.
What is OKN and what does it assess?
Optokinetic nystagmus - objective measure reflex eye movement in response to moving stripes (The infant’s eyes will only track a moving target to a certain distance, at which point their eyes snap back to fixate on a new target.) — used to assess binocular function and motion detection in non-verbal infants.
How does vision change over time after birth?
Birth: blurry, poor contrast, ~20/400 acuity
6 months: huge improvement in acuity, binocularity, tracking
1 year: near adult-level accommodation and depth perception
7–8 years: visual system matures fully
