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Anatomy/Neuro-Anatomy of the Visual System

Anatomy/Neuro-Anatomy of the Visual System. Medical ppt. http://hastaneciyiz.blogspot.com. Learning Objectives. Describe the function of major structures of the visual system Describe major milestones in development of the visual system

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Anatomy/Neuro-Anatomy of the Visual System

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  1. Anatomy/Neuro-Anatomy of the Visual System Medical ppt http://hastaneciyiz.blogspot.com

  2. Learning Objectives • Describe the function of major structures of the visual system • Describe major milestones in development of the visual system • Describe normal age related changes in vision and their impact on occupational performance • Describe changes in visual function associated with pathology

  3. Eye as a camera

  4. Structures of the Eye and Orbit The anterior visual system

  5. Orbit • Eyeball • Optic nerve • Extraocular muscles • Other nerves • Blood vessels • Lacrimal gland • Fat • Connective tissue

  6. Eyelids and Eyelashes • Protect eye from foreign bodies • Help limit light into the eye • Functions as part of the lacrimal system • Blinking squeezes tears from lacrimal gland • Tears fill in uneven surfaces of cornea • Nourishes and protects cornea

  7. Eyeball has three layers Outer protective layer • Sclera and cornea Middle vascular layer • Uveal tract • Consists of iris, ciliary body and choroid Inner sensory layer • Retina

  8. Sclera • Encloses eyeball except for cornea • Extension of the dura mater of CNS • Protects inner contents of eye and • Helps maintain shape of the eye • Extraocular muscles attach to its surface

  9. Cornea • Avascular • Transparent • 5 layers • Protects inner contents of eye • Refracts light

  10. Aqueous • Continuously produced & drained away • trabecular meshwork • canal of Schlemm • Maintains health of lens and cornea • Maintains shape & pressure within eye

  11. Iris • Pigmentation protects retina • Controls pupil aperture • Dilator muscle sympathetic control • Spincter muscle

  12. Lens • 65% water 35% protein • Avascular • Refracts light to focus image onto retina • Fibers form throughout life

  13. Ciliary Body • Ciliary muscle • Shapes lens • Controlled by CN III • Ciliary process • Secretes aqueous

  14. Vitreous • Maintains transparency and form of eye • Holds retina in place

  15. Conjunctiva • Thin transparent membrane covering sclera and inner eyelid • Provides protection and moisture • Many blood vessels, few pain fibers • Conjunctivitis common condition

  16. Choroid • Vascular supply for eye • Capillaries and veins

  17. Retina Directionof light • Lines posterior 2/3rd of eye • Distant receptor organ • 5 layers • Inside out arrangement

  18. Rod Receptor Cells Rod Cells • Concentrated in periphery • Activate in low illumination • Detect general form, not details • Provide background information

  19. Cone Receptor Cells Cone Cell • Capture detail and color • Require direct stimulation • Bright light’ • Concentrated in fovea

  20. Retinal Pigment Epithelium (RPE) RPE Layer • Works with Bruchs membrane and choroid layer • Maintains health of receptor cells • Breakdown causes build up of cellular debris

  21. Retinal Processing Pathway Axons form Optic nerve Ganglion cells Bipolar cells • Impulses converge onto bipolar cells • Converge again onto ganglion cells • Axons of ganglion cells merge and exit at optic disc

  22. Optic nerve • CN II • Each nerve contains 1 million plus heavily myelinated ganglion axons • Macular fibers inside peripheral fibers outside

  23. Visual Field • Visual field • 160-180 degrees horizontally • 120 degrees vertically • Practical field of vision • Head and eye movement • 270 degrees

  24. Hill of Vision Concept

  25. Visual Field Diagram

  26. Extraocular Muscles (EOM) Sup. oblique • Medial rectus • Lateral rectus • Superior rectus • Inferior rectus • Superior oblique • Inferior oblique Sup. rectus Med. rectus Lat. rectus Inf. rectus Inf. oblique

  27. Cranial Nerves Controlling Extraocular Eye Muscles • CN III Oculomotor • CN IV Trochlear • CN VI Abducens

  28. Oculomotor Nerve (3) • Innervates 5 muscles • Medial, superior,and inferior rectus muscles, inferior oblique • Levator palpebrae superioris • Internal musculature of the eye • Ciliary muscle (lens) • Spincter muscle (pupil)

  29. Trochlear Nerve (4) • Innervates superior oblique • Down and out muscle of eye

  30. Abducens Nerve (6) • Innervates lateral rectus • Abducts eye

  31. Birds Eye View of Visual Pathways

  32. Development of the Visual System

  33. Visual system develops from three types of tissue • Neuroectodermal from brain • Becomes retina, iris and optic nerve • Surface ectoderm of head • Forms lens • Mesoderm • Forms vascular supply and sclera

  34. Embryonic Eye Development 3-4 weeks gestation The eye begins as a groove in the neural fold on the cranial end of the embryo

  35. Over the next week, the groove turns inside out and balloons outward and creates a hollow bulb projecting from each side of the neural tube

  36. At 4 weeks, the bulb and stalk are fully formed. The lateral surface of the bulb begins to flatten and the ectoderm thickens to become the lens placode

  37. The placode turns in on itself to form a deep indentation (the lens pit). The ends of the pit come to together to form the lens vesicle, which then is pinched off to become the lens.

  38. At the same time, the optic vesicle begins to fold in on itself to form a double walled, bowl shaped structure called the optic cup. The two walls fuse together, the outside wall becomes the RPE, the inside wall be- comes the sensory retina. The axons of the ganglion cells converge into the optic stalk to become the optic nerve.

  39. Retina Cornea Lens Optic nerve

  40. Rim of optic cup eventually becomes the ciliary body and muscle, iris, dilator and sphincter muscles • Mesenchyme cells develop into the choroid and sclera-both are extensions of vascular and fibrous structures within brain • Sclera-continuation of dura mater • Choroid-continuation of pia arachnoid • Form a sheath around the optic n.

  41. The relationship between these structures explains why an increase in cerebral spinal fluid after brain injury can be diagnosed by observing the optic disc for papilledema

  42. Maturation of Face and Eyes • As the embryo develops, the eyes migrate from the sides to the front as the face matures • Face is formed by 14 weeks • During development, structures may fail to fully form or to close completely • Creates many of the congenital eye conditions observed in children

  43. Rods and Cones 25 wks-both begin to develop Optic Tract 28-38 wks-begins to myelinate Superior Colliculus Basic structure develops 16-28 wks Rods and Cones 4 mos-complete with rods finishing first Optic Tract Rapid myelination first 2 mos continued for 2 years Superior Colliculus Myelination completed at 3 mos Maturation of Visual SystemPre-natal Post-natal

  44. LGN Matures after birth GC Tracts Myelination begins at birth LGN Process takes 9 mos Stereoscopic vision at 3-4 mos GC Tracts Completed in 4-5 mos Maturation of Visual SystemPre-natal Post-natal

  45. Visual cortex 25-28 wks-starts dendritic growth, increasing synaptic density, cortical layers develop Visual cortex Doubles in density first 2 years, adult synaptic density and functional maturity by age 11 Maturation of Visual SystemPre-natal Post-natal

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