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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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