Anatomy

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

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

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 Check this part of outline-incompleteCheck this part of outline-incomplete

13. Lens 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

18. Retina Lines posterior 2/3rd of eye Distant receptor organ 5 layers Inside out arrangement

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

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

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

22. Retinal Processing Pathway Impulses converge onto bipolar cells Converge again onto ganglion cells Axons of ganglion cells merge and exit at optic disc

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

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

27. Extraocular Muscles (EOM) Medial rectus Lateral rectus Superior rectus Inferior rectus Superior oblique Inferior oblique

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

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

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 SystemPre-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

65. Pathology of the Visual System

66. Anterior visual system has three jobs to do Focus the image on the retina Capture the image (encode it) Transmit the image to the CNS

67. Sharp focusing of image on retina depends on: Sufficient refraction of light rays entering the eye Focal point established on the fovea Transparency of all intervening structures between outside of eye and retina Adequate illumination

68. Sufficient Refraction of Light Rays entering the Eye

70. Hyperopia

71. Myopia

72. Smoothness of Refracting Surfaces Astigmatism Cornea is spoon shaped or dimpled Light rays are unevenly refracted Can develop with trauma and age Corrected for optically with cylinder Cataract Dead cells deposited in lens, calcify Begins in periphery, progressing to center Surface becomes pitted Causes light scatter and veiling glare Eventually complete opacity

73. Closeness of Object As object comes closer, focal point on retina is pushed back

74. Closeness of Object As object comes closer, focal point on retina is pushed back

75. Accommodation 3 step process Convergence Lens thickens Pupil constricts to reduce light scatter Controlled by CN III Affected by lens Presbyopia Aphakia

76. Control of Light Scatter Light rays are refracted more strongly in periphery than center of lens Causes wild and scattered light rays Reduced by blocking peripheral rays with pupillary constriction Increases acuity Pinpoint vision

77. Transparency of Intervening Structures Any opacity in cornea, aqueous, lens, vitreous will prevent image from reaching retina Common conditions Corneal scarring Cataract Trauma-vitreous hemorrhage Also causes veiling glare

78. Adequate Illumination Retina must be adequately diffused with light to capture an image Amount of light is controlled by pupil Any condition affecting responsiveness of pupil will affect Tolerance of light Ability to rapidly adjust to changes in light Opacity in intervening structures also affects amount of light entering eye

79. Ability of retina to capture image Retinal function can be affected by disease, injury or congenital conditions Macular degeneration, diabetic retinopathy, retinitis pigmentosa, retinal detachment Damaged retina creates blind spot in vision Known as a scotoma Performance limitations depend on area of retina damaged Peripheral vs. central

80. Macular Scotoma Area of reduced light sensitivity within central 20 degrees of the visual field

81. Macular Scotoma Occurs with retinal diseases Affects ability to See small details Discriminate contrast Discriminate color Primary pathology dealt with in patients with low vision 83% of patients referred for low vision services found to have dense macular scotomas regardless of disease

82. Scanning Laser Ophthalmoscope

83. Central Scotoma Scotoma impinges on and involves the fovea

84. Para-central Scotoma Within the central 20 degrees of the field but not involving the fovea

85. Ring Scotoma Surrounds the fovea on 4 sides

86. Scotomas may vary in density Dense No response to light Relative/Threshold Responds to light if bright enough

87. Adaptation to Scotoma Scotoma creates a hole in visual field Deprives CNS of vision needed to identify objects CNS adapts using various mechanisms Perceptual completion Metamorphopsia Development of PRL

88. Perceptual Completion Perception in which objects or a visual scene appears complete despite missing visual input Example of top down �cognitive processing� where we see something because we expect to see it

91. Scotomas less than 5 degrees CNS can perceptually complete Example: own blind spot Person unaware of presence of scotoma Scotomas greater than 5 degrees CNS will attempt to perceptually complete but may not be successful Person does not perceive black hole but instead a blurriness or inability to bring object into focus

92. Metamorphopsia Scotoma is too big to complete perceptually Objects appear warped or misaligned

93. Preferred Retinal Locus (PRL) If scotoma covers fovea, CNS adopts an eccentric retinal area to act as a pseudo-fovea for visual tasks previously completed by the fovea Develops within 24 hours of loss of fovea

96. 40% place PRL above the scotoma on the retina(leaves lower portion of field clear)

97. 35% place PRL to the right (leaves left side of page clear)

98. 20% place PRL to left

99. 7% place PRL below

100. Person may develop more than one PRL and use a different one depending on task and lighting conditions Ability to use PRL to direct eye movements is more highly correlated to reading ability than other visual function Although person develops PRL, he/she may not be aware of it Important to assess ability to use PRL

101. Peripheral Visual Field Deficit Person also exercises perceptual completion May be completely unaware of deficit Will not interfere with perception of visual details (acuity) But will affect mobility Reduces detection of motion and form

102. Ability of optic nerve to transmit visual input Can be damaged by disease, trauma and congenital conditions Glaucoma Optic neuritis Head injury Can lose all or part of field Depending on location, extent of damage

104. Deficits in Posterior Visual System

105. Visual Field Deficits Lesions along geniculocalcarine tracts or in occipital lobe Most common cause in adult is stroke Posterior cerebral artery (PCA) Pure visual stroke (sometimes affects language) Middle cerebral artery (MCA) Mix of motor, sensory, visual, cognitive Lesion behind LGN will always cause homonymous loss

108. Homonymous Hemianopsia

109. Hemianopsia with Macular Sparring

110. Cortical Blindness Also called cortical visual impairment CVI Damage is so significant in occipital lobe, CNS is not able to complete any cortical processing of vision

111. Person loses:

112. Person loses: Object identification through visual system Visual orientation to space Cognitive application of vision

113. Person retains

114. Person retains Subcortical processing of vision Navigational vision Vision for safety Other sensory processing Haptic discrimination Auditory discrimination

115. Alteration of Visual Attention Difficulty arousing attention Difficulty attending globally Difficulty attending to details Difficulty sustaining attention Difficulty dividing/shifting attention Asymmetrical attention Unilateral spatial neglect

116. Diminishment of Attention Has pervasive effect on cognition Person takes in information in incomplete disorganized fashion CNS cannot properly analyze incoming information Decision making is based in incomplete and/or incorrect information Garbage in - garbage out