1. Sight Visual Accessory Organs eyelids lacrimal apparatus
extrinsic eye muscles
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2. Eyelid palpebra composed of four layers orbicularis oculi - closes
skin
muscle
connective tissue
conjunctiva
orbicularis oculi - closes
levator palperbrae superioris – opens
tarsal glands – secrete oil onto eyelashes
conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball
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3. Lacrimal Apparatus lacrimal gland lateral to eye secretes tears
canaliculi
collect tears
lacrimal sac
collects from canaliculi
nasolacrimal duct
collects from lacrimal sac
empties tears into nasal cavity
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4. Extrinsic Eye Muscles Superior rectus rotates eye up and medially
Inferior rectus
rotates eye down and medially
Medial rectus
rotates eye medially
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5. Extrinsic Eye Muscles Lateral rectus rotates eye laterally
Superior oblique
rotates eye down and laterally
Inferior oblique
rotates eye up and laterally
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6. Structure of the Eye hollow spherical wall has 3 layers
outer fibrous tunic
middle vascular tunic
inner nervous tunic
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7. Outer Tunic Cornea anterior portion transparent light transmission
light refraction
Sclera
posterior portion
opaque
protection
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8. Middle Tunic Iris anterior portion pigmented controls light intensity
Ciliary body
anterior portion
pigmented
holds lens
moves lens for focusing
Choroid coat
provides blood supply
pigments absorb extra light
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9. Anterior Portion of Eye
filled with aqueous humor
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10. Lens transparent biconvex lies behind iris
largely composed of lens fibers
elastic
held in place by suspensory ligaments of ciliary body
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11. Ciliary Body forms internal ring around front of eye
ciliary processes – radiating folds
ciliary muscles – contract and relax to move lens
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12. Accommodation
changing of lens shape to view objects
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13. Iris composed of connective tissue and smooth muscle
pupil is hole in iris
dim light stimulates radial muscles and pupil dilates
bright light stimulates circular muscles and pupil constricts
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14. Aqueous Humor fluid in anterior cavity of eye
secreted by epithelium on inner surface of the ciliary body
provides nutrients
maintains shape of anterior portion of eye
leaves cavity through canal of Schlemm
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15. Inner Tunic retina contains visual receptors
continuous with optic nerve
ends just behind margin of the ciliary body
composed of several layers
macula lutea – yellowish spot in retina
fovea centralis – center of macula lutea; produces sharpest vision
optic disc – blind spot; contains no visual receptors
vitreous humor – thick gel that holds retina flat against choroid coat
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16. Layers of Retina
receptor cells, bipolar cells, and ganglion cells - provide pathway for impulses triggered by photoreceptors to reach the optic nerve
horizontal cells and amacrine cells – modify impulses
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17. Light Refraction Refraction bending of light
occurs when light waves pass at an oblique angle into mediums of different densities
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18. Types of Lenses Convex lenses cause light waves to converge
Concave lenses cause
light waves to diverge
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19. Focusing On Retina as light enters eye, it is refracted by
convex surface of cornea
convex surface of lens
image focused on retina is upside down and reversed from left to right
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20. Visual Receptors Rods long, thin projections
contain light sensitive pigment called rhodopsin
hundred times more sensitive to light than cones
provide vision in dim light
produce colorless vision
produce outlines of objects
Cones
short, blunt projections
contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe
provide vision in bright light
produce sharp images
produce color vision
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21. Rods
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22. Visual Pigments Rhodopsin light-sensitive pigment in rods
decomposes in presence of light
triggers a complex series of reactions that initiate nerve impulses
impulses travel along optic nerve
Pigments on Cones
each set contains different light-sensitive pigment
each set is sensitive to different wavelengths
color perceived depends on which sets of cones are stimulated
erythrolabe – responds to red
chlorolabe – responds to green
cyanolabe – responds to blue
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23. Stereoscopic Vision provides perception of distance and depth
results from formation of two slightly different retinal images
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24. Visual Pathway
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