1. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Eye and Associated Structures  70% of all sensory receptors are in the eye  Most of the eye is protected by a cushion of fat and the bony orbit  Accessory structures include:  Eyebrows  Eyelids  Conjunctiva  Lacrimal apparatus  Extrinsic eye muscles

2. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Eyebrows  Coarse hairs that overlie the supraorbital margins  Functions include:  Shading the eye  Preventing perspiration from reaching the eye  Orbicularis muscle – depresses the eyebrows  Corrugator muscles – move the eyebrows medially

3. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Conjunctiva  Transparent membrane that:  Lines the eyelids as the palpebral conjunctiva  Covers the whites of the eyes as the ocular conjunctiva  Lubricates and protects the eye

4. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lacrimal Apparatus  Consists of:  lacrimal gland  associated ducts  Lacrimal glands:  secrete tears  Tears  Contain mucus, antibodies, and lysozyme  Enter the eye via superolateral excretory ducts  Exit the eye medially via the lacrimal punctum  Drain into the nasolacrimal duct

5. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lacrimal Apparatus Figure 15.2

6. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Extrinsic Eye Muscles  Six straplike extrinsic eye muscles  Four rectus muscles:  originate from the annular ring  Two oblique muscles:  move the eye in the vertical plane

7. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Extrinsic Eye Muscles Figure 15.3a, b

8. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.3c Summary of Cranial Nerves and Muscle Actions  Names, actions, and cranial nerve innervation of the extrinsic eye muscles

9. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of the Eyeball  A slightly irregular hollow sphere  Has anterior and posterior poles  The wall is composed of three tunics:  Fibrous  Vascular  sensory  The internal cavity is:  filled with fluids called humors  The lens separates the internal cavity into:  Anterior segment  posterior segment

10. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of the Eyeball Figure 15.4a

11. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Fibrous Tunic  Forms the outermost coat of the eye and is composed of:  Opaque sclera (posteriorly)  Clear cornea (anteriorly)  The sclera:  Protects the eye  Anchors extrinsic muscles  The cornea:  Lets light enter the eye

12. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Vascular Tunic (Uvea): Choroid Region  The vascular tunic has three regions:  Choroid  Ciliary body  Iris  Choroid region:  A dark brown membrane  Forms the posterior portion of the uvea (vascular tunic)  Supplies blood (nutrients) to all eye tunics

13. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Vascular Tunic: Ciliary Body  A thickened ring of tissue  Surrounds the lens  Composed of smooth muscle bundles (ciliary muscles)  Anchors the suspensory ligament  The suspensory ligament holds the lens in place

14. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Vascular Tunic: Iris  The colored part of the eye  The central opening of the iris forms the pupil  The pupils:  Regulate the amount of light entering the eye  Constrict in:  Close vision  Bright light  Dilate in:  Distant vision  Dim light

15. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pupil Dilation and Constriction Figure 15.5

16. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Tunic: Retina  A delicate two-layered membrane:  Pigmented outer layer:  Absorbs light preventing its scattering  Neural layer containing:  Photoreceptors that transduce light energy  Bipolar cells  Ganglion cells  Amacrine  Horizontal cells

17. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Tunic: Retina Figure 15.6a

18. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Retina: Ganglion Cells and the Optic Disc  Ganglion cell axons:  Run along the inner surface of the retina  Leave the eye as the optic nerve  The optic disc:  Is the site where the optic nerve leaves the eye  Lacks photoreceptors (the blind spot)

19. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Retina: Ganglion Cells and the Optic Disc Figure 15.6b

20. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Retina: Photoreceptors  Rods:  Respond to dim light  Are used for peripheral vision  Cones:  Respond to bright light  Have high-acuity color vision  Are found in the macula lutea  Are concentrated in the fovea centralis

21. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  Break Slide  Biol2401.33248  Mon 04/15/’13

22. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Blood Supply to the Retina  The neural retina receives its blood supply from two sources  The choroid supplies the outer third  The central artery and vein supply the inner two- thirds  Small vessels radiate out from the optic disc:  Can be seen with an ophthalmoscope

23. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Inner Chambers and Fluids  The lens separates the internal eye into:  Anterior segment  Posterior segments  The posterior segment is filled with:  A clear gel called vitreous humor  The viterous humor:  Transmits light  Supports the posterior surface of the lens  Holds the neural retina firmly against the pigmented layer  Contributes to intraocular pressure

24. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Anterior Segment  Composed of two chambers  Anterior chamber:  Between the cornea and the iris  Posterior:  Between the iris and the lens  Aqueous humor:  A plasmalike fluid that fills the anterior segment  Drains via the scleral venous sinus (Schlemm canal)  Supports, nourishes, and removes wastes

25. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Anterior Segment Figure 15.8

26. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lens  A biconvex, transparent, flexible, avascular structure  Allows precise focusing of light onto the retina  Is composed of epithelium and lens fibers  Lens epithelium:  Anterior cells that differentiate into lens fibers  Lens fibers:  Cells filled with the transparent protein crystallin  With age, the lens:  Becomes more compact & dense  Loses its elasticity

27. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Light  Electromagnetic radiation  Wide spectrum energy waves (gamma rays to radio)  Our eyes respond to the visible spectrum  Different cones in the retina respond to:  Different wavelengths of the visible spectrum

28. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Light Figure 15.10

29. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Refraction and Lenses  Light bends on passing through a convex lens (eye lens)  The rays converge to a focal point  The formed image is:  Upside down  Reversed right to left

30. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Refraction and Lenses Figure 15.12a, b

31. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Focusing for Distant Vision  Light from a distance needs little adjustment for proper focusing  Far point of vision:  The distance beyond which the lens does not need to change shape to focus (20 ft.) Figure 15.13a