2. Lesson 3 Our eyes work in a way that is similar to a camera. Like the click of a camera lens, in the blink of an eye images are formed in the process of vision. Eye Care

3. Lesson 3 Identify the parts of the eye. Understand how the eye forms visual images. Examine the effects of health behaviors on the eye. Describe different types of eye problems. In this lesson, you’ll learn to: Lesson Objectives

4. Lesson 3 Structure of the Eye Your Eyes The eyebrows, eyelashes, and eyelids protect the eyes from foreign particles and bright light. Each eye has a group of structures that make and allow drainage of tears. One of these structures is the lacrimal gland. lacrimal gland As you blink, tears are moved across the surface of the eye. Tears keep the surface of the eyeball moist and clear of foreign particles.

5. Lesson 3 Optic Nerve and Three Layers of the Eyeball Wall Parts of the Eye

6. Lesson 3 The Outer Layer The outermost layer of the eye is made up of the sclera and the cornea.scleracornea The sclera is composed of tough, fibrous tissue that protects the inner layers of the eye and supports and shapes the eyeball. At the front of the eye is the cornea. Parts of the Eye

7. Lesson 3 The Middle Layer Within the middle layer of the eyeball is the choroid and the iris.choroid The muscles of the iris control the size of the pupil. In bright light the pupil constricts and in dim light it enlarges to let in more light. Parts of the Eye

8. Lesson 3 The Inner Layer The light-sensitive cells in the retina are called rods and cones, each named for its basic shape. retina When light stimulates these cells, a nerve impulse travels to the brain via the optic nerve, which is located at the back of the eye. Behind the iris and the pupil is the lens of the eye. Parts of the Eye

9. Lesson 3 The Process of Image Formation Image formation begins as light passes through the cornea, pupil, and lens and reaches the retina. Light rays are first focused by the curved cornea, and then the focus is refined by the lens. Muscles attached to the lens contract or relax to change its shape. Light stimulates rods and cones in the retina, and a nerve impulse is transmitted to the brain through the optic nerve. Vision

10. Lesson 3 How You View Objects Click image to view animation. Vision

11. Lesson 3 Sharpness of Vision The sharpness of vision can be measured by reading an eye chart. If you have 20/20 vision, you can stand 20 feet away from an eye chart and read the top eight lines. If you have 20/60 vision, you can see the chart from 20 feet the way a person with normal vision would see it from 60 feet. Reading an eye chart measures only one aspect of vision. Vision

12. Lesson 3 Ways to Keep Your Eyes Healthy Follow a well-balanced diet. Protect your eyes. Have regular eye exams. Rest your eyes regularly. Healthy Eyes

13. Lesson 3 Vision Problems Two common vision problems reflect the inability of the eye to properly focus light on the retina. MyopiaHyperopia Myopia, or nearsightedness, results in a person not being able to see distant objects clearly. Hyperopia, or farsightedness, results in a person being able to see distant objects clearly, while near objects appear blurred. These conditions can be corrected with glasses or contact lenses. Eye Problems

14. Lesson 3 Other Vision Problems Astigmatism: Because of an irregularly curved cornea or lens, the eye is not able to focus properly, resulting in images that appear blurry. Strabismus: If the muscles of the eyes are weak or don’t function properly, strabismus may result. Eye Problems

15. Lesson 3 Diseases of the Eye Sties: A sty is an inflamed swelling of a sebaceous gland near the eyelash. Conjunctivitis or pinkeye: This is an inflammation of the conjunctiva, a thin membrane that covers the sclera lining of the eyelids. Detached Retina: This occurs if a portion of the retina is separated from the choroid as a result of natural aging or from an injury. Treatment includes using a laser to repair a tear or surgery to reattach the retina. Eye Problems

16. Lesson 3 Serious Eye Diseases Glaucoma: In glaucoma, abnormally high pressure inside the eyeball leads to irreversible damage of the retina and the optic nerve and can result in loss of sight. Cataracts: In this condition, the normally transparent lens becomes cloudy. Macular Degeneration: This condition occurs when the light-sensing cells of the macula, the portion of the retina directly opposite the lens, begin to malfunction. Eye Problems

17. Lesson 3 Q. The retina is the light-sensitive membrane on which images are cast by the _________. 1.sclera 2.cornea 3.choroid 4.lacrimal gland Choose the appropriate option. Quick Review

18. Lesson 3 A. The retina is the light-sensitive membrane on which images are cast by the cornea. Click Next to attempt another question. Quick Review - Answer

19. Lesson 3 Provide a short answer to the question given below. Q. List the structures that make up the three layers of the eyeball wall. Click Next to view the answer. Quick Review

20. Lesson 3 A. The structures that make up the three layers of the eyeball wall are as follows: 1. Outer: Sclera and cornea 2. Middle: Choroid, iris, pupil 3. Inner: Retina Click Next to attempt another question. Quick Review - Answer

21. Lesson 3 Provide a short answer to the question given below. Q. Explain the difference between myopia and hyperopia. Click Next to view the answer. Quick Review

22. Lesson 3 A. Myopia is nearsightedness—when near objects are clear and distant objects are blurry. Hyperopia is farsightedness—when near objects are blurry and distant objects are clear. Click Next to attempt another question. Quick Review - Answer

23. Lesson 3 How might having night blindness affect a person’s activities? Analyze the following question. Quick Review

24. Lesson 3 A. Correct! The retina is the light-sensitive membrane on which images are cast by the cornea. Click Next to attempt another question. Quick Review - Answer

25. Lesson 3 You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer. Quick Review - Answer

26. Lesson 3 The eyebrows, eyelashes, and eyelids protect the eyes from foreign particles and bright light. Each eye has a group of structures that make and allow drainage of tears. One of these structures is the lacrimal gland. lacrimal gland As you blink, tears are moved across the surface of the eye. Tears keep the surface of the eyeball moist and clear of foreign particles. Structure of the Eye The lacrimal gland is the gland that secretes tears into ducts that empty into the eye. Your Eyes

27. Lesson 3 The Outer Layer The outermost layer of the eye is made up of the sclera and the cornea. The sclera is composed of tough, fibrous tissue that protects the inner layers of the eye and supports and shapes the eyeball. At the front of the eye is the cornea. The sclera is the tough, white part of the eye. Parts of the Eye

28. Lesson 3 The outermost layer of the eye is made up of the sclera and the cornea. The sclera is composed of tough, fibrous tissue that protects the inner layers of the eye and supports and shapes the eyeball. At the front of the eye is the cornea. The cornea is a transparent tissue that bends and focuses light before it enters the lens. The Outer Layer Parts of the Eye

29. Lesson 3 The Middle Layer Within the middle layer of the eyeball is the choroid and the iris. The muscles of the iris control the size of the pupil. In bright light the pupil constricts and in dim light it enlarges to let in more light. The choroid is a thin structure that lines the inside of the sclera. Parts of the Eye

30. Lesson 3 The light-sensitive cells in the retina are called rods and cones, each named for its basic shape. retina When light stimulates these cells, a nerve impulse travels to the brain via the optic nerve, which is located at the back of the eye. Behind the iris and the pupil is the lens of the eye. The retina is the light-sensitive membrane on which images are cast by the cornea. The retina is the light-sensitive membrane on which images are cast by the cornea. The Inner Layer Parts of the Eye