Visuele ontwikkeling
Van het netvlies naar de hersenschors STAAFJES: perifeer zicht zien in het duister KEGELTJES: Centrale visus Kleurzicht
Visueel systeem: prenatale ontwikkeling
Refractive errors • The average refractive error in children from birth to 1 year of age is about 2 diopters (D) of hyperopia . • Astigmatism up to 2 D is common in children under 3 years of age. • Low amounts of anisometropia are common and variable in infants.
Rechtstreeks uit het hersenweefsel Prosencefalon - optische blaasjes Optische zenuw later dan het oog Myelinisatie start bij chiasma opticum
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Retina
Visual acuity
• Foveal region gets to be thinner ( 1000лm --700 лm ) by 4 yrs. • Cones density/area increases by age. • More peripheral retina develops faster than foveal area. • X,Y,W ganglion cells.
• the spatial resolving capacity of the visual system . • Spatial resolution= angular resolution =describes the resolving power of the eye. • Resolving power is the ability of the components of an imaging device( e.g: eye) to measure the angular separation of the points in an object .
Visual acuity
Visual acuity
• Visual acuity is limited by diffraction, aberrations and photoreceptor density in the eye . • a number of factors also affect visual acuity such as refractive error, illumination, contrast and the location of the retina being stimulated.
• Target detection requires only the perception of the presence or absence of an aspect of the stimuli . • Landolt C and the Illiterate E are forms of detection used in visual acuity measurement in the clinic.
Visual acuity
6/6 (20/20)
• Target recognition tasks
logMAR
logMAR
Vernier acuity
Grating acuity
• Vernier acuity is the ability by a person to detect the proper alignment of two line segments
• Angular acuity = Reading a letter • Morphoscopic acuity =Reading a letter in a line. • Crowding phenomena=
• aspect of visual acuity involving the ability to distinguish the elements of a fine grating composed of alternating dark and light stripes or squares .
Development of visual acuity • Visual acuity
• • • • •
contrast sensitivity
Birth ≈ 6/300 3 months 6/90 --- 6/60 1 yr ≈ 6/24 2 yrs ≈ 6/12 --- 6/9 3 yrs ≈6/9 ---6/6
unknown ≈ 6/60 ≈ 6/9 ≈ 6/6 ≈ 6/6
• Saccadic system • Smooth pursuit system • Optokinetic nystagmus
Visual milestones • Babies are not born with all the visual abilities they need in life . • The ability to focus their eyes, move them accurately, and use them together as a team must be learned . • Eye and vision problems in infants can cause developmental delays.
Birth-4 mo • Up to about 3 months of age, babies' eyes do not focus on objects more than 2-3 meters from their faces. • By eight weeks, babies begin to focus their eyes on the faces of a parent or other person near them. But they still cannot follow. • For the first two months of life, an infant's eyes are not well coordinated , However, if an eye appears to turn in or out constantly, an evaluation is warranted. • Babies should begin to follow moving objects with their eyes and reach for things at around four months of age.
• Not every child is the same and some may reach certain milestones at different ages.
5-8 months • During these months, control of eye movements and eyebody coordination skills continue to improve. • Depth perception is not present at birth. It is not until around the fifth month that the eyes are capable of working together to form a three-dimensional view of the world and begin to see in depth. • it is generally believed that babies have good color vision by five months of age. • Most babies start crawling at about 8 months old, which helps further develop eye-hand-foot-body coordination. Early walkers who did minimal crawling may not learn to use their eyes together as well as babies who crawl a lot.
9-12 months
12-24 months
• At around 9 months of age, babies begin to pull themselves up to a standing position. By 10 months of age, a baby should be able to grasp objects with thumb and forefinger.
• By two years of age, a child's eye-hand coordination and depth perception should be well developed.
• By twelve months of age, most babies will be crawling and trying to walk. Parents should encourage crawling rather than early walking to help the child develop better eye-hand coordination. • Babies can now judge distances fairly well and throw things with precision.
9-12 months
• Children this age are highly interested in exploring their environment and in looking and listening. They recognize familiar objects and pictures in books and can scribble with pencil.
Twee visuele systemen ontwikkelen…
• At around 9 months of age, babies begin to pull themselves up to a standing position. By 10 months of age, a baby should be able to grasp objects with thumb and forefinger. • By twelve months of age, most babies will be crawling and trying to walk. Parents should encourage crawling rather than early walking to help the child develop better eye-hand coordination.
• Primair/retinocorticaal visueel systeem • Subcorticaal/retinotectaal visueel systeem
• Babies can now judge distances fairly well and throw things with precision.
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The retinotectal system
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12
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CORTEX : functionele gebieden
Retinotectaal systeem • Zien wat je eigenlijk niet ziet • Orienteringsgedrag
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34
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VISUELE BAAN
22-10-2009
Creatief kijken
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Zodoende leidt een letsel in de bovenste linker hersenkwab achteraan tot
Primair visueel systeem • Op de visuele hersenschors mooie weergave van het netvlies • Geeft omtrek, bestaan van een voorwerp aan • Info aan verderop liggende gebieden is nodig voor interpretatie
…. gezichtsveldverlies rechts onder in beide ogen.
6/6
6/18
These simulated visual acuities show how detail is lost with reduced acuity
Postgraduaat 2010
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6/120
6/500
These simulated contrast sensitivities show that the detail is present, but the picture is ‘washed out’.
22-10-2009
Creatief kijken
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Newborn babies have a preference for the way living things move
Postgraduaat 2010
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Form coherence stimulus
Postgraduaat 2010
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22-10-2009
Motion coherence stimulus
Creatief kijken
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Postgraduaat 2010
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Zien en doen is een mirakel
Postgraduaat 2010
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Postgraduaat 2010
Color perception • Bilateral representation • Representation in V1 and V4 • Children with CVI and CP prefer – Color over grey – Moving over nonmoving stimuli – Color over moving stimuli – Color/movement conjunctions over color or movement alone Postgraduaat 2010
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Maturatie bij kinderen
Maturatie van de visus
• Attention – From 2 months onward
• Object perception – From 4 months (cfr BSID-II)
• Line orientation (?) • Colour perception (?) • Facial recognition – From birth
• Motion perception – biological motion from 8 months onward
• Visuomotor integration – From 2 months onward
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Newborn babies have a preference for the way living things move
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Belangrijke basisvaardigheden • • • •
Detectie Aandacht Herkenning Interpretatie
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Gevolgen uitval visueel-cognitief • Dorsale stroom (parietaal) – Gestoorde simultaanperceptie – Problemen met waarnemen van bewegende voorwerpen – Problemen met bewegen in 3D – Gestoorde ooghandcoordinatie – Crowding
Oorzaken
Gevolgen uitval visueel-cognitief • Ventrale stroom rechts – Gestoorde orientatie (topografische agnosie) – Gestoorde herkenning van (mimiek van) gezichten
• Ventrale stroom links – Gestoorde vormherkenning – Gestoord lezen
Tekort aan zuurstof/bloedsvoorziening voor, rond of kort na de geboorte Craniaal trauma Infecties van de hersenen en hersenvliezen Stofwisselingsstoornissen Gestoorde aanleg van de hersenen Syndromen (VeloCardioFaciaal Syndroom, Williams) 68
Diagnosestelling anno 2009 Oogartsonderzoek • Oogheelkundig onderzoek • Kinderneurologisch onderzoek • Neuropsychologisch onderzoek
• • •
– IQ profiel – Visueel profiel – Gestandaardiseerde neuropsychologische testbatterijen
•
• Structureel hersenonderzoek • Hersenfunctie-onderzoek
• • •
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Detectie ≠ Orientatie !
Van het oog tot voor de cortex Lichtreflex Breking van de lens – Bijziend/ verziend Fundus – Oogzenuw: verdunning geeft aanleiding tot verminderde gezichtsscherpte Gezichtsscherpte en gezichtsveld Kleurenzicht Contrastgevoeligheid
Geassocieerde oogproblemen (65%)
Visual crowding • occurs when a visual object (such as a letter) is surrounded by other similar objects. As a result, these objects are harder to identify.
• Verminderde gezichtsscherpte – Geeft weer in hoeverre het visueel systeem in staat is om details waar te nemen – Nl 10/10; slechtziend 3/10; blind 1/20 – Vergelijking raster - optotypes
• Gezichtsveld – Deel van de buitenwereld dat we kunnen zien als we een punt fixeren
Geassocieerde oogproblemen
Functioneel • ElektroRetinoGram (netvlies) • VEP (hersenactiviteit)
• Scheelzien
• Schokkende oogbewegingen (nystagmus)
CORRECTIE INDIEN MOGELIJK
Kinderneurologisch onderzoek
NMR van de hersenen • • • •
Neurologisch onderzoek Somatisch onderzoek Globale ontwikkeling Motorische vaardigheden
• Beschadiging van de witte stof • Cysten of zones van weefselverlies in de grijze stof • Grootte van de hersenkamers • Stoornis in de aanleg van de hersenen
– Grof – Fijn
• Oogvolgbewegingen 77
Newly defined sum score
CVI-kliniek • Kinderneurologisch onderzoek • Oogonderzoek • Neuropsychologische testing – L-94 • Computertaakjes met hoge visueel perceptuele belasting
– Gezichtsherkenningstaak
09/12/2011
Cerebral Visual Impairment
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TVPS- DTVP Form coherence stimulus
Figure ground
Visual closure
Motion coherence stimulus
Visual memory
Form constancy
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VBA data (term (10) ~ preterm (20)) Is interventie zinvol?
• Geen leeftijdsgrens • Kinderen voordeel van de twijfel geven • Doel = vergroten wendbaarheid van het visueel systeem – Stimuleren – Faciliteren – Compenseren
09/12/2011
Cerebral Visual Impairment
89
Begeleidingsmogelijkheden • Thuisbegeleiding – Ganspoel – Spermalie
• GON-begeleiding vanuit type 6 • Buitengewoon onderwijs type 6 • specifiek volgens individuele mogelijkheden/moeilijkheden ISBN:
9033451425
