1. Sight Visual Accessory Organs eyelids lacrimal apparatus extrinsic eye muscles

2. Eyelid palpebra composed of four layers 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

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

4. Extrinsic Eye Muscles Superior rectus rotates eye up and medially Inferior rectus rotates eye down and medially Medial rectus rotates eye medially

5. Extrinsic Eye Muscles Lateral rectus rotates eye laterally Superior oblique rotates eye down and laterally Inferior oblique rotates eye up and laterally

6. Structure of the Eye hollow spherical wall has 3 layers outer fibrous tunic middle vascular tunic inner nervous tunic

7. Outer Tunic Cornea anterior portion transparent light transmission light refraction Sclera posterior portion opaque protection

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

9. Anterior Portion of Eye filled with aqueous humor

10. Lens transparent biconvex lies behind iris largely composed of lens fibers elastic held in place by suspensory ligaments of ciliary body

11. Ciliary Body forms internal ring around front of eye ciliary processes – radiating folds ciliary muscles – contract and relax to move lens

12. Accommodation changing of lens shape to view objects

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

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

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 (you move your eye to put images here) Only cones (no rods) optic disc – blind spot; contains no visual receptors vitreous humor – thick gel that holds retina flat against choroid coat

16. Posterior Cavity contains vitreous humor – thick gel that holds retina flat against choroid coat

17. Vision Pass through: –Cornea –Aqueous humor –Lens –Vitreous humor –Retinal layers –Photoreceptor cells

18. Major Groups of Retinal Neurons 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

19. Layers of the Eye

20. Light Refraction Refraction bending of light occurs when light waves pass at an oblique angle into mediums of different densities

21. Types of Lenses Convex lenses cause light waves to converge Concave lenses cause light waves to diverge

22. 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

23. 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

24. Rods and Cones

25. 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

26. Rod Cells

27. Stereoscopic Vision provides perception of distance and depth results from formation of two slightly different retinal images

28. Visual Nerve Pathway

29. Life-Span Changes Age related hearing loss due to damage of hair cells in organ of Corti degeneration of nerve pathways to the brain tinnitus Age-related visual problems include dry eyes floaters (crystals in vitreous humor) loss of elasticity of lens glaucoma cataracts macular degeneration

30. Clinical Application Refraction Disorders concave lens corrects nearsightedness (myopia) convex lens corrects farsightedness (hyperopia)