Introduction to Vision Implications for the developing child

What is Vision? Our ability to see helps us to gather information on: Form Colour Movement Depth

Vision: Key Questions How do we detect depth given that the back of the eye is a two dimensional sheet and that depth perception is not directly preserved from the outset?

Vision: Key Questions How do we register shape in a way that allows us to recognise familiar objects under varying circumstances – including when parts are missing or added?

Vision: Key Questions What is the relationship between vision and mental imagery? What aspects of visual perception are learned? What does it mean to ‘see’ something?

Sequence of visual learning First Awareness First Attention to Light First Fixation Then Attention Then Understanding Then People Then Objects Then Tracking

Sequence of visual learning First interest in distant objects First Peripheral Then near objects Then Central Vision

Sequence of visual learning First preference for familiar First viewing part of an object Then preference for novel stimuli Then viewing whole of object

Sequence of visual learning First interest in simple items and designs First interest in large items Then interest in complex items and designs Then interest in small items

Beginnings The eyeballs develop during the 12 th week of gestation The eyes are part of the brain Seeing is a learnt and dynamic process Seeing is highly personal

Beginnings Vision is affects and is affected by, the whole body and personality

The importance of vision Vision is only one of the five senses but greater reliance is placed on it than all the other senses put together.

Function Human eyes evolved to give good eyesight in daylight

Eyes Eyeballs are spherical - diameter 23mm Eyeballs maintain their shape by means of a fluid called aqueous at the front and a jelly like substance called vitreous in the main body

Functional Vision Relies on: Spatial analysis Temporal analysis Cognitive analysis

Seeing Believing and Knowing Perception: The foundation of coming to know about our world Memory: The ways we retain and build on knowledge Mediation: The bridges between aspects of perception

Parts of the Eye 1 The Front or “window” - cornea, iris,lens 2 Middle - globe 3 Innermost coat - the retina which contains rods and cones

Visual acuity The ability to discriminate high-contrast fine detail at a distance The power of the eye to distinguish form The sharpness and clarity of vision

Assessment Distance Near Field of vision Colour vision

Implications Near vision – N number (usually smallest size child can read) Field – the area that can be seen from all parts of the eye when looking ahead Colour – common red/green confusion Contrast sensitivity – need for clear definition (central vision issues)

Visual Systems Two streams in development– where and what Three streams of processing – where, what and how

Ventral and Dorsal Streams One stream for perceptual processing and one stream for controlling actions Ventral Pathways – contain specialised areas for face perception (who) Dorsal Stream – controls eye movements, reaching and grasping (how)(action)

A Typical Visual Child: 3-5 years Can: See in detail with good contrast sensitivity and accommodation See in colour See in depth Keep eyes straight

A Typical Visual Child: 3-5 years See all around whilst maintaining interest on target centrally Move the eyes in controlled fashion – Further refinement takes place 8-12 years The critical period: Up to 9-10 months

Intervention 1. Front of Eye – intervention + 2. Eye globe – intervention Back of globe/neural path --?

Overall Impact of Visual Impairment Range and variety of experience The ability to get about The control of the environment and self in relation to it

Individual Differences Related To Degree of vision Cause of visual impairment Age and type of onset Present condition Personality

DEFINITIONS Snellen (1869) – acuity and field loss VI – visual acuity less than 6/18 but better or equal to 6/60 Severe VI – visual acuity of less than 6/60 but better or equal to 3/60 Blind – visual acuity of less than 3/60

Degree of Vision Total blindness Partial Sight/Low Vision

Causation Ocular Cerebral

Age and Type of Onset Congenital Acquired Sudden Gradual Stable Degenerative