2. Structure & Function of the Eye External Features 1.Soft tissue that must be protected 2.Cells exposed to air must not be allowed to dry out 3.Should have the ability to select a direction to sample 4.Should have the ability to control the amount of light entering the eye

3. Structure & Function of the Eye External Features 1.Soft tissue that must be protected 2.Cells exposed to air must not be allowed to dry out 3.Should have the ability to select a direction to sample 4.Should have the ability to control the amount of light entering the eye

4. Structure & Function of the Eye External Features 1.Soft tissue that must be protected 2.Cells exposed to air must not be allowed to dry out 3.Should have the ability to select a direction to sample 4.Should have the ability to control the amount of light entering the eye

5. Structure & Function of the Eye External Features 1.Soft tissue that must be protected 2.Cells exposed to air must not be allowed to dry out 3.Should have the ability to select a direction to sample 4.Should have the ability to control the amount of light entering the eye

6. 1. Protecting the Soft Tissues The eye is located in a bone socket. Why is there a hole in the back of the eye socket?

7. 1. Protecting the Soft Tissues The _________ help filter out dust

8. 1. Protecting the Soft Tissues The eyelashes help filter out dust

9. 1. Protecting the Soft Tissues The eyelashes help filter out dust The ______ can close and cover the eye.

10. 1. Protecting the Soft Tissues The eyelashes help filter out dust The eyelid can close and cover the eye.

11. 1. Protecting the Soft Tissues The eyelashes help filter out dust The eyelid can close and cover the eye. The eye is covered by a tough thick skin called the ___________

12. 1. Protecting the Soft Tissues The eyelashes help filter out dust The eyelid can close and cover the eye. The eye is covered by a tough, thick, opaque skin called the sclera

13. 2. Keeping the eye Moist The ______________ lies within the orbit on the outer portion of the upper eye. The gland continually secretes ____ which moisten, lubricate, and protect the surface of the eye. Excess tears drain into __________ which empty into the __________.

14. 2. Keeping the eye Moist The lachrymal gland lies within the orbit on the outer portion of the upper eye. The gland continually secretes ____ which moisten, lubricate, and protect the surface of the eye. Excess tears drain into __________ which empty into the __________.

15. 2. Keeping the eye Moist The lachrymal gland lies within the orbit on the outer portion of the upper eye. The gland continually secretes tears which moisten, lubricate, and protect the surface of the eye. Excess tears drain into __________ which empty into the __________.

16. 2. Keeping the eye Moist The lachrymal gland lies within the orbit on the outer portion of the upper eye. The gland continually secretes tears which moisten, lubricate, and protect the surface of the eye. Excess tears drain into small ducts which empty into the __________.

17. 2. Keeping the eye Moist The lachrymal gland lies within the orbit on the outer portion of the upper eye. The gland continually secretes tears which moisten, lubricate, and protect the surface of the eye. Excess tears drain into small ducts which empty into the nasal cavity.

18. 2. Keeping the eye Moist The lachrymal gland lies within the orbit on the outer portion of the upper eye. The gland continually secretes tears which moisten, lubricate, and protect the surface of the eye. Excess tears drain into small ducts which empty into the nasal cavity. Why do you think we have to blow our nose when we cry?

19. 3. Controlling Direction A set of 6 muscles control the direction the eye is pointed

20. 4. Controlling the Amount of Light Entering the Eye The _____ is the hole. The ____ is a muscle that can be contracted or relaxed to change hole size.

21. 4. Controlling the Amount of Light Entering the Eye The pupil is the hole. The ____ is a muscle that can be contracted or relaxed to change hole size.

22. 4. Controlling the Amount of Light Entering the Eye The pupil is the hole. The iris is a muscle that can be contracted or relaxed to change hole size.

23. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 16.5b Accessory Structures of the Eye Lacrimal apparatus – keeps the surface of the eye moist – Lacrimal gland – produces lacrimal fluid – Lacrimal sac – fluid empties into nasal cavity

24. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Fibrous Tunic Most external layer of the eyeball – Composed of two regions of connective tissue Sclera – posterior five-sixths of the tunic – White, opaque region – Provides shape and an anchor for eye muscles Cornea – anterior one-sixth of the fibrous tunic Limbus – junction between sclera and cornea Scleral venous sinus – allows aqueous humor to drain

25. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Medial View of the Eye Figure 16.7a