Chapter 8 Visual System l Chris Rorden University

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Chapter 8 Visual System l Chris Rorden University of South Carolina Norman J. Arnold

Chapter 8 Visual System l Chris Rorden University of South Carolina Norman J. Arnold School of Public Health Department of Communication Sciences and Disorders University of South Carolina 1

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Apparent motion 3

Apparent motion 3

Visual Perception Events Refraction of light rays by lens and cornea l Conversion of

Visual Perception Events Refraction of light rays by lens and cornea l Conversion of electromagnetic energy of light to nerve impulse l Transmission of action potential to CNS l Perception of visual image in visual cortices l 4

Terminology l Optic Nerve – l Optic Tract – l Visual fibers from retina

Terminology l Optic Nerve – l Optic Tract – l Visual fibers from retina to optic chiasm Optic fibers between chiasm to lateral geniculate body of thalamus or fibers that bypass thalamus to superior colliculus Optic Radiation – Fibers project to visual cortex via geniculocalcarine fibers (optic radiation) 5

Visual Pathway l Cortical and subcortical processing 6

Visual Pathway l Cortical and subcortical processing 6

Visual Field: area you see before you - outside world l Retinal Field: Focused

Visual Field: area you see before you - outside world l Retinal Field: Focused representation of visual field l – Reversed (right/left, up/down) Monocular Visual Field: Lateral portion perceived in only one eye l Binocular Visual Field: Common area seen by both eyes l 7

Eyeball Weighs 7. 5 g and 2. 4 cm long l 5/6 in orbital

Eyeball Weighs 7. 5 g and 2. 4 cm long l 5/6 in orbital cavity l Anterior Chamber filled with aqueous humor l – – – Made by choroid plexus of the ciliary processes Drains through canal of Schlemm Need to maintain pressure and link to circulatory system 8

Cavities and Chambers of Eyeball Anterior chamber Posterior chamber Anterior cavity Retina Posterior cavity

Cavities and Chambers of Eyeball Anterior chamber Posterior chamber Anterior cavity Retina Posterior cavity Choroid Vitreous humor Fovea Sclera Optic disk Optic nerve Macula lutea 9

Ocular Layers l Fibrous Tunic (blue) – – l Vascular Tunic (yellow) – –

Ocular Layers l Fibrous Tunic (blue) – – l Vascular Tunic (yellow) – – – l Sclera: White of eye Cornea: Nonvascular and transparent fibrous region of eye Choroid Iris Ciliary Body Nervous Tunic (red) – Retina: Rods and Cones 10

Functions l Lens – l Ciliary Muscle – l Focuses images on the Retina

Functions l Lens – l Ciliary Muscle – l Focuses images on the Retina Aqueous humor Cornea Regulates changes by lens (near and far vision) Pupil Iris – Controls pupil size Iris Lens Ciliary body Vitreous humor 11

Pupil, Iris, Scelera Pupil l Iris l Scelera l 12

Pupil, Iris, Scelera Pupil l Iris l Scelera l 12

Anatomy of Retina l Rods – l Cones – – l l l Night

Anatomy of Retina l Rods – l Cones – – l l l Night vision 3 types: sensitive to long, medium and short wavelength Often red, green, blue but actual peak sensitivity is yellow, yellowish-green, and blue Bipolar Cells Ganglion Cells Light passes through cell layers and then back to the ganglion cells. 13

Photo receptors http: //www. webexhibits. org/colorart/ganglion. html http: //web. mit. edu/bcs/schillerlab/research/A-Vision/A 3 -1. html

Photo receptors http: //www. webexhibits. org/colorart/ganglion. html http: //web. mit. edu/bcs/schillerlab/research/A-Vision/A 3 -1. html 14

Illusions from the retina 15

Illusions from the retina 15

Blindspot There are no rods or cones in the optic disk. l Close your

Blindspot There are no rods or cones in the optic disk. l Close your right eye, and look at the 'x' in the figure. Move either closer or further away from the screen until you notice that circle with the dot inside vanishes altogether. l 16

Photosensors l Cones (30 million) – – – l Rods (100 million) – –

Photosensors l Cones (30 million) – – – l Rods (100 million) – – l Discriminate color and sharp vision Cone cells in macula lutea fovea centralis Discriminate in dim light Sensitive to shape and movement Lateral peripheral retina You can often see things better at night if you do not look directly at them! We will not cover photochemistry of retina and optical mechanism. 17

Central Visual Mechanism Visual pathway from retina to primary visual cortex l Optic nerve

Central Visual Mechanism Visual pathway from retina to primary visual cortex l Optic nerve fibers exit optic foramina and move to optic chiasm l Optic tract move to lateral geniculate body (Remember it is part of thalamus) l Travel to occipital lobe to visual cortex l 18

Visual Pathway l l l Each eye sees both left and right visual field.

Visual Pathway l l l Each eye sees both left and right visual field. Ipsilateral information crosses over at optic chiasm. Some connections to superior colliculi. – l Reflexive eye movments Others go to thalamus (lateral geniculate nuclei) and then cortex. 19

Retinal Representation l Nasal and temporal visual fields – l l When you are

Retinal Representation l Nasal and temporal visual fields – l l When you are looking at an object, these form the medial (nasal) and lateral (temporal) hemifield of vision for each eye. Reversed to opposite halves of retinal representative fields Also inverted Nasal visual fields project to temporal retinal fields and do not cross at optic chiasm Temporal visual field project to nasal retinal fields and cross at optic chiasm 20

Lateral Geniculate Nucleus to Visual Cortex l Optic Radiation (geniculocalcarine fibers; Meyer’s Loop) runs

Lateral Geniculate Nucleus to Visual Cortex l Optic Radiation (geniculocalcarine fibers; Meyer’s Loop) runs under temporal lobe to occipital lobe Lateral Geniculate Nucleus (Thalamus) V 1 Primary Visual Cortex (BA 17) 21

Reflexes l Pupillary Light Reflex – – – l Involves Edinger-Westphal Nucleus and oculomotor

Reflexes l Pupillary Light Reflex – – – l Involves Edinger-Westphal Nucleus and oculomotor CN (III) Pupil contracts with light (consensual response) Damage to system may be due to Horner’s syndrome (always constricted pupil) or CN III lesion damage to afferents to one eye Accommodation Reflex: The focus reflex – – – Modifies lens curvature when object moves closer to eyes Lens flexibility important Lens tends to become less flexible around age 45 22

Horner’s syndrome l Injury to sympathetic nervous system – – – l First-order neuron

Horner’s syndrome l Injury to sympathetic nervous system – – – l First-order neuron disorder: Central lesions that involve the hypothalamospinal pathway (e. g. transection of the cervical spinal cord). Second-order neuron disorder: Preganglionic lesions (e. g. compression of the sympathetic chain by a lung tumor). Third-order neuron disorder: Postganglionic lesions at the level of the internal carotid artery (e. g. a tumor in the cavernous sinus). ptosis (drooping eyelid), miosis (constricted pupil) and dilation lag. 23

Clinical Conditions l Hypermetropia (farsightedness) – – l Can see distant objects normally but

Clinical Conditions l Hypermetropia (farsightedness) – – l Can see distant objects normally but problem in near objects Due to short eyeball and inadequate refractory power of the lens Myopia (nearsightedness) – – Can see near objects but not distant Due to abnormally long eyeball and too strong refractory power 24

Clinical Conditions l Astigmatism – – – Focus disorder of vertical and horizontal rays

Clinical Conditions l Astigmatism – – – Focus disorder of vertical and horizontal rays Caused by irregular shape or the cornea, lens, or both Can typically be corrected with glasses with relatively cylindrical rather than dish shaped lenses. Standard Cylindrical 25

Clinical conditions l Color vision disorders (usually males) – – – First documented by

Clinical conditions l Color vision disorders (usually males) – – – First documented by John Dalton (1798) Dichromacy: Loss single type of cone, e. g. of long (yellow, protanopia), medium (yellow-green, deuteranopia) or short (blue, tritanopia) wavelength. Monochromacy: Total color blindness due to absence of cones or abnormal cones Normal Protanopia Deuteranopia Tritanopia 26

l Art by Jay Lonewolf Morales 27

l Art by Jay Lonewolf Morales 27

Other Common Disorders Presbyopia - decrease in vision with age l Cataract - Increase

Other Common Disorders Presbyopia - decrease in vision with age l Cataract - Increase in protein in lens l Glaucoma - Increased intraocular pressure l Infections - Inflammation of the eye l Retinitis Pigmentosa - familial disorder causing loss of rod cells. Includes peripheral visual loss and night blindness l 28

Visual defects following stroke l l Damage to early visual centers causes blindness (see

Visual defects following stroke l l Damage to early visual centers causes blindness (see next slides). Damage to temporal/parietal lobes cause: – – – Neglect: failure to respond to contralesional stimuli (usually right hemisphere injury) Achormatopsia: color blindness Akinetopsia: Motion blindness (very rare) Agnosia: failure to recognize objects Ataxia: reaching deficits Simultanagnosia: only see one thing at a time Neglect Agnosia: can copy But not recognize 29

V 1 (BA 17) l l Primary visual cortex (V 1) lies in calcarine

V 1 (BA 17) l l Primary visual cortex (V 1) lies in calcarine fissure. Complete damage leads to Homonymous hemianopia. Partial damage leads to scotomas Point-to-point mapping with retina. 30

Types of Field Defects Left optic tract carries info from right visual field in

Types of Field Defects Left optic tract carries info from right visual field in each eye l Right optic tract carries info from left visual field in each eye l Simplified in that some overlapping present l 31

Types of Field Defects L R A B C D E F A Monocular

Types of Field Defects L R A B C D E F A Monocular blindness B Bitemporal hemianopsia C Nasal hemianopsia D Homonymous hemianopia E Homonymous left Superior quadrantopsia F Homonymous left Inferior quadrantopsia 32

Visual Field Defects l Homonymous – – l Similar regions affected in each eye

Visual Field Defects l Homonymous – – l Similar regions affected in each eye i. e. Right visual fields of both eyes Heteronymous – – Different regions affected in each eye i. e. Left visual field of one eye and right visual field of other eye 33

Specific Deficits l l l Monocular Blindness: Blindness in one eye due to optic

Specific Deficits l l l Monocular Blindness: Blindness in one eye due to optic nerve lesion before optic chiasm Bitemporal (Heteronymous) Hemianopsia: Loss of temporal visual fields of each eye, lesion at optic chiasm Nasal Hemianopsia: Loss of nasal vision in one eye due to lesion in lateral edge of optic chiasm. Homonymous Hemianopsia: Loss of left or right visual fields for both eyes due to lesion in right optic tract Upper Left Quadrantanopsia: Loss of vision in left upper quadrant of each eye due to lesion in Meyer’s Loop Lower left Quadrantanopsia: Loss of vision in lower left quadrant of each eye due to lesion in medial fibers of visual tract 34