Post natal pereception development

POST NATAL PERECEPTION DEVELOPMENTGREESHMA G

MPHIL OPTOMETRY

Developmental aspectsBirth – not fully matured

Proper maturation- exposure to normal environment is required

Ocular dominanceMost binocular cortical neurons do not receive inputs from two eyes

Closure of an eye of an immature animal results in a lack of cortical cells driven by the deprived eye

Critical/ sensitive period

•Period in which visual system is influenced by environmental manipulation

•During critical period cortical cells of eye will compete

No binocular action- No stereopsis

Ocular Dominance

Nu

mb

er

of

cells

4 5 6 7321

Contralateral Ipsilateral

OCULAR DOMINANCE HISTOGRAM

Ocular Dominance

Nu

mb

er

of

cells

4 5 6 7321

Contralateral Ipsilateral

First five weeksR L

Ocular Dominance

Nu

mb

er

of

cells

4 5 6 7321

Contralateral Ipsilateral

Six week through ten weeksR L

MONOCULAR DEPRIVATION DURING THE CRITICAL PERIOD CAN LEAD TO AN ASSYMETRICAL OCULAR DOMINANCE COLUMN

Synopsis of critical period- Hubel’s and weisel’s experiment

Synaptic connectivity in the in the cortex is strengthened by the neural activity and lack in the neural activity result in weakening of this connections

Amblyopia •Reduction in vision secondary to monocular deprivation during the critical period

•Amblyopia results from the abnormal cortical development, not an abnormality of eye

•It can occur secondary to• Anisometropia

• Strabismus

AMBLYOPIA

Occlusion amblyopia

-One eye occluded in critical period

-Monocular congenital cataract

-Lid ptosis

Anisometropic amblyopia

-Unequal refractive errors

Strabismic amblyopia

-Constant unilateral strabismus present

during critical period

-Diplopia

-Suppression

Meridional amblyopia

-Cortical neurons are orientation selective

-Meridional astigmatism

Alternating strabismus

Development of refractive error in humansFirst years of life- <2.50D hyperopic

Age- months Average visual acuity

1 20/638

1.5 20/540

2.5 20/278

4 20/224

6 20/106

9 20/88

12 20/93

18 20/70

24 20/63

30 20/52

36 20/28

48 20/24

VISUAL ACUITY IN EARLY LIFE

Post natal vision

NEONATE

• 8 to 14 inches

• 20/200 - 20/600

• Mothers arm to her eyes

1-3 MONTH

• Start gazing at objects

• 2 months- eye’s coordination develop

• Hand-eye coordination

• Color perception

4-7 MONTH

• Enjoys more complex designs

• Till 1 meter

• Fine movement of objects

8-12 MONTH

• Focuses on a toy, crawl pull it and picks it

• Grasp and throw objects

• Can perceive depth

1 YEAR

• Depth perception continues

Contrast sensitivity

Stereopsis•Infant- Preferential looking test

•Rapid onset between 3 and 6 months

•6 months- 1 min of arc

Spatial visionVernier acuity

•Preferential looking

•Develops more slowly in late years

•Depends on cortical processing

•Adult levels at slightly older ages (6–8 years of age)

Grating acuity

•Preferential looking

•Forced choice

•1 month- 20/600

•1 year- 20/100

•Adult levels at 3- 5years – 20/20

PREFERENTIAL LOOKING TEST

Temporal Vision: Critical Flicker Fusion Frequency•40 Hz at 1 month

•55 Hz by 3 months- adult level

The retinal and cortical immaturities that slow the

development of grating and Vernier acuity apparently have

little effect on the maturation of temporal resolution

Scotopic Sensitivity•Adult-like at 1 month of age

•Shape of the function- Characteristics of rhodopsin

•Does not depend on postreceptoral processing

•Scotopic sensitivity- 507 nm

•Reaches adult levels by approximately 6 months

Colour Vision•Red–green discrimination arises during the second month of life

•Blue–yellow discrimination

•Adult like on the 1 year of life

•Photopic spectral sensitivity function is adult-like in young infants

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