The document describes the anatomy and development of the visual system. It begins with an overview of the structures of the eye and orbit, including the eyelids, sclera, cornea, iris, lens, vitreous, retina, and optic nerve. It then discusses the embryonic development of the eye from the neural tube and the maturation of the visual system prenatally and postnatally. Finally, it outlines common age-related changes in vision such as reduced visual acuity and accommodation, increased floaters and light needs, and declines in contrast sensitivity, color perception, and visual attention.

1. Anatomy/Neuro-Anatomy of
the Visual System

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

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

7. 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

8. 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

9. 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

10. Cornea
• Avascular
• Transparent
• 5 layers
• Protects inner
contents of eye
• Refracts light
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11. Aqueous
• Continuously produced
& drained away
• trabecular meshwork
• canal of Schlemm
• Maintains health of lens
and cornea
• Maintains shape &
pressure within eye

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

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

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

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

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

17. Choroid
• Vascular supply for
eye
• Capillaries and veins
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18. Retina
• Lines posterior 2/3rd of eye
• Distant receptor organ
• 5 layers
• Inside out arrangement
Direction of light

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

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

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

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

23. Optic nerve
• CN II
• Each nerve contains
1 million plus heavily
myelinated ganglion
axons
• Macular fibers inside
peripheral fibers
outside
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24. Visual Field
• Visual field
• 160-180 degrees horizontally
• 120 degrees vertically
• Practical field of vision
• Head and eye movement
• 270 degrees

25. Hill of Vision Concept

26. Visual Field Diagram

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

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

29. 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)

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

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

32. Birds Eye View of Visual
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36. Development of the
Visual System

37. 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

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

39. 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

40. 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

41. 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.

42. 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.

43. Len
sOptic
nerve
Retina Cornea

44. • 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.

45. 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

46. 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

48. Maturation of Visual System
Pre-natal Post-natal
• 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

49. Maturation of Visual System
Pre-natal Post-natal
• 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

50. Maturation of Visual System
Pre-natal Post-natal
• 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

51. Eye Movement
• Able to fixate and make basic eye
movements by 2-3 months
• 2 years to obtain good control
• Up to 9 years to obtain complex control

52. Visual Acuity
• Newborn
• 20/200, sees best in 2-75 cm range
• 3 months
• 20/60
• 6 months
• 20/20
• 2 years
• Acute near vision-fine motor skills develop

53. Normal Age Related Changes
in Vision

54. Reduced Visual Acuity
• Static acuity
• Decreases to 20/30-20/40
• Prevalence 40% by age 70
• Dynamic acuity
• Decrease may be due to reduced OM
control

55. Loss of Accommodation
• A.k.a. presbyopia
• Result of compacting of protein fibers in
center of lens
• Lens thickens and loses flexibility
• Occurs gradually beginning in 40s
• Creates need for bifocal

56. Floaters
• Strands of protein which float in vitreous
• Float more easily in old eye because
vitreous is more fluid
• More noticeable in bright light
• Generally benign unless accompanied
by bright flashes of light or significant
increase in number

57. Dry Eyes
• Lacrimal glands do not make enough or
make poor quality tears
• More prevalent in women
• Can be exacerbated by medication
• Causes itchiness, burning, decreased
acuity
• Treated with artificial tears or surgery

58. Increased Need for Light
• Pupil diameter decreases
• A.k.a. senile miosis
• Lens thickens becoming more yellow
• Combined-these two conditions reduce
the amount of light coming into eye
• 80 yr old person needs 10x as much
light as an average 23 year old

59. Susceptibility to Glare
• Lens and cornea become less smooth
• Lens & vitreous develop protein strands
• Combine to cause light scatter
• Increased discomfort and disability
• Lose acuity under glare condition
• Also takes longer to recover from glare

60. Reduced Dark/Light Adaptation
• Takes longer to reform and store
pigments
• Never reach same level of dark
adaptation as younger person
• More difficult to go from bright to dark
than dark to bright

61. Reduced Contrast Sensitivity
• Caused by changes in color and density
of lens and decreased pupil aperture
• 75 year old needs 2x as much contrast
as younger person
• 90 year old needs 10x as much contrast

62. Reduced Color Perception
• Caused by yellowing of lens
• Decrease in sensitivity at violet end of
spectrum
• White objects may appear yellow

63. Reduced Visual Field
• Changes in facial structure
• Nose grows??
• Orbit loses fat and eye sinks in

64. Reduced Visual Attention
• Decline in ability to
• Attend to objects in complex, dynamic
arrays
• Simultaneously monitor central and
peripheral visual fields
• Diameter of visual field decreases
• 90 yr olds-40% have an attentional field of
less than 20 degrees