Visual Development an introduction Riyad Banayot.pptx

Visual Development an introduction Riyad Banayot

1. Visual Development Dr. Riyad Banayot

2. Visual Cortex Scientists discovered columns of neurons that selectively respond to visual information from one eye or the other. They learned that normal visual experience during a critical period in early childhood is crucial for these columns to form properly The visual cortex is located in the occipital lobe (lower rear portion of the brain's hemispheres) Nerve connections from the eye to the visual cortex, where visual information is processed

3. Physiology of the visual pathway The ability to focus a visual image on the central retina develops at about two to three months of age. Ideally, all rays of light converge on the macula, the retinal area where images can be most sharply delineated. Accommodation is the process by which the ciliary body contracts, allowing the lens to assume a greater curvature and to increase refraction of light rays from near objects. Accommodation is reflexively linked to turning in of the eyes, or ocular convergence, so that a binocular image is maintained.

4. Physiology of the visual pathway When moving in unison, each eye focuses the retinal image on its macula, and the cortical image in the occipital brain is reconciled into binocular "seeing." If the retinal image is distorted in one eye because of a refractive difference between eyes (anisometropia) or a congenital cataract, or if the visual axis misaligns the image on the retina (strabismus), the cortical image is too dissimilar to permit clear binocular resolution.

5. Physiology of the visual pathway The brain quickly learns to suppress the poorer image from the affected eye to allow for clear vision. Since cortical visual development is dependent on continuous stimuli, neurodevelopment is impeded in the visual cortex corresponding to the suppressed eye. The result can be permanent visual impairment (amblyopia) in an otherwise normal eye. This process is dynamic and reverses if the distortion of the retinal image is corrected; the earlier the correction, the more likely full development can be achieved.

6. Normal Development Acuity at birth is 6/120 Age 6 months V/A is 6/6 Color vision improves by 3 months Eye color evolves by 9-12 months Iris is lightest in color at birth

7. Normal Visual Development Visual acuity at birth is quite poor, typically around 6/120 . This is due to immaturity of the central nervous system visual pathways and visual processing areas. Visual acuity improves to 6/30 by four months of age, and this is the critical period of visual development. Visual acuity reaches nearly 6/6 by 12 months of age, but special techniques are needed to demonstrate it. A cooperative 3-year old should demonstrate a visual acuity of 6/12, and a 5-year old 6/9.

8. Neuroanatomy LGN synthesizes input from both eyes Lack of input from one eye can damage stereo vision and acuity (binocular vision) “Critical Period”

9. Critical Period “Period” early in infancy when the visual system is sensitive to deprivation

10. Critical Period 1st phase: - Birth to 10 months - Rapid development - Highly susceptible to insult - Responsive to treatment 2nd phase: - 1 – 9 yrs - Slower change - Rehabilitation prognosis poorer

11. Normal Visual Development Many newborns show variable ocular alignment: 70% having exotropia (eye turns out) and 30% having straight eyes Esotropia (eye turns in) is rare. By 2 - 3 months of age, most infants will have straight eyes. Misaligned eyes beyond 3 months of age require ophthalmic evaluation

12. Schedule of Recommended Pediatric Vision Screening Based on Patient Age Neonate External (penlight) examination for surface abnormalities of the eye and surrounding tissues Ocular alignment (corneal reflections) Ophthalmoscopy for red reflexes

13. Schedule of Recommended Pediatric Vision Screening Based on Patient Age Age six months Ability to fix and follow light, face or small toy External (penlight) examination for surface abnormalities of the eye and surrounding tissues Pupillary examination Ocular alignment (corneal reflections) Ophthalmoscopy for red reflexes

14. Schedule of Recommended Pediatric Vision Screening Based on Patient Age Age 3 - 4 years Visual acuity by picture chart or tumbling E chart External (penlight) examination for surface abnormalities of the eye and surrounding tissues Pupillary examination Ocular motility and alignment (ocular movements, cover test and corneal reflections) Ophthalmoscopy for red reflexes and examination of retina and optic nerve

15. Schedule of Recommended Pediatric Vision Screening Based on Patient Age Age 5 - 6 years Visual acuity by Snellen method External (penlight) examination for surface abnormalities of the eye and surrounding tissues Pupillary examination Ocular motility and alignment (ocular movements, cover test and corneal reflections) Ophthalmoscopy for red reflexes and examination of retina and optic nerve