Healthy Eyes and Ears – Varsity Education

The eyes and their supporting structures are a complex of parts.

Most of the sensory information that travels to your brain comes from light signals received by your eyes. Structurally, your eyes sit in bony sockets, called orbits, at the front ofyour skull. A layer of fat cushions each eyeball inside its socket.

Another structure is the lacrimal gland, which secretes tears into the eye through ducts. Tears are made of water, salts, mucus, and a substance that protects the eye from infection. As you blink, tears are moved across the surface of the eye.They keep the surface of the eyeball moist and clear of foreign particles.

Parts of the Eye

The eye consists of the optic nerve and three layers of the eyeball wall, as shown in Figure 13.8.

Screen Shot 2020-08-03 at 12.58.38 PM.png

The outermost layer of the eye is made up of the sclera and the cornea. The sclera (SKLEHR-uh), the white part ofthe eye, is composed oftough, fibrous tissue that protects the inner layers of the eye. The cornea at the front of the eye, is a transparent tissue that bends and focuses light before it enters the lens.
Within the middle layer of the eye wall is the choroid (KOHR-oid), a thin structure that lines the inside of the sclera. Also within the middle layer is the iris, the col- ored portion of the eye that contains the pupil. The pupil is the hole through which light reaches the inner eye.In bright light, the pupil constricts; in dim light, it enlarges, or dilates, to let in more light.
The retina is the inner layer of the eye wall. The retina con- tains millions oflight-sensitive cells called rods and cones. Rods allow us to see in dim light. Cones function in bright light and allow us to see color. When light stimulates these cells, a nerve impulse travels to the brain through 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 lens is transparent and helps refine the focus of images on the retina. The area between the cornea and the lens is filled with a watery fluid called aqueous humor, which provid~s nutrients to the eye. Between the lens and retina there is a cavity filled with a gelatin-like substance called vitreous humor. This helps the eyeball stay firm and keep its shape, and holds the retina against the choroid.

Vision

When light passes through the cornea, pupil, and lens to reach the retina, an image forms. Light rays are first focused by the curved cornea, then later refined by the lens onto the retina. This light stimulates the rods and cones in the retina, sending nerve impulses to the brain through the optic nerve. The brain translates the nerve impulses into images that you recognize.

Your vision may be affected by the way images are pro- duced on the retina. Having clear, or 20/20, vision means that the images are produced clearly and sharply on your retina. This means that you can stand 20 feet away from an eye chart and read the top eight lines. When the images produced on your retina are not clear, an eye doctor will perform tests to determine what type of disorder is affecting your vision. Two common vision disorders are nearsightedness, or myopia,and farsightedness, or hyperopia.

If you have 20/60 vision, you must be 20 feet from the chart in order to read it the way a person with normal vision can read it from 60 feet. A person with 20/60 vision is said to be nearsighted, which means being able to see close, but not far. Other components of vision include eye coordination, Peripheral or side vision, and depth perception.

Screen Shot 2020-08-03 at 1.00.49 PM.png

Keeping Your Eyes Healthy

Main Idea: Making healthy choices will keep your eyes healthy.

Eye problems are outlined in Figure 13.9. You can practice several healthful behaviors to help keep your eyes healthy.

• Follow a well-balanced eating plan. Include foods that contain vitamin A, such as carrots and sweet potatoes. Deficiency in vitamin A could result in night blindness-the inability to see well in dim light.

Protect your eyes. Wear safety goggles when participating m activities m which your eyes could be injured. Kee dirty hands or other objects such as makeup applicators p away from your eyes to reduce the risk of infection and injury. Wear sunglasses that block UV light, and never look directly into the sun or bright lights.
Rest your eyes regularly. Take regular breaks when using the computer or reading. Looking up and away every 10 minutes reduces eyestrain.
Get regular eye exams. Routine eye exams enable health care professionals to detect and treat eye disease in its early stages.

In some cases when a cornea is diseased, a corneal transplant may be recommended. Corneal transplants can restore vision and reduce pain. It is the most commonly performed transplant surgery in the United States.

Your Ears

Main Idea: The inner, middle, and outer ear work together so you can hear.

The ear can be divided into three main sections, each with its own unique structures. The parts of the ear are shown in Figure 13.10.

Screen Shot 2020-08-03 at 1.03.04 PM.png

- The Outer Ear. The outer ear is the visible part ofthe
  ear, called the auricle. It channels sound waves into the external auditory canal. This canal leads to the remain- ing portion of the outer ear, called the eardrum. The skin ofthis canal is lined with tiny hairs and glands that produce wax that protect the ear from dust and foreign objects. The eardrum, also called the tympanic mem- brane, acts as a barrier between the outer and middle ear.
- The Middle Ear. Directly behind the eardrum are the auditory ossicles, three small bones linked together that connect the eardrum to the inner ear. The auditory ossi- cles are the smallest bones in the body. The middle ear is connected to the throat by the eustachian tube. When you swallow or yawn, this tube allows pressure to be equalized on each side of the eardrum.
- The Inner Ear. The inner ear, or labyrinth, consists of a network of curved and spiral passages that can be divided into three main parts. The cochlea, a spiral- shaped canal, is the area of hearing in the inner ear. The vestibule and the semicircular canals are where balance is controlled.

Hearing and Balance

Receptors in your inner ear are stimulated by a sound wave. The impulse is then sent to your brain, where it is interpreted as a sound. These sound waves enter the external auditory canal, causing the eardrum to vibrate.The vibrations cause fluid in the cochlea to move, which stimulate receptor cells. These cells send a nerve impulse to the brain, where sound is interpreted. As this is occurring, receptor cells in the vestibule and the semicircular canals send messages to the brain about your sense of balance. Tiny hairs located in the ear sense movement and send nerve impulses to the brain. The brain makes adjustments to maintain balance.

Keeping Your Ears Healthy

Main Idea: Caring for your ears helps prevent irritation, injury, infection, and damage to the ears, as well as hearing loss.

To protect your hearing, have your ears examined by a health care professional if you suspect an infection. Middle ear infections can damage the structure of the ear, but can be treated with antibiotics. Other ways to protect your hear- ing include wearing a hat that covers both the auricles and the earlobes in cold weather. Wear protective gear, such as a batting helmet, when playing sports. Keep foreign objects, including cotton-tipped swabs, out of the ear canal.

Preventing Hearing Loss

Exposure to loud noises can lead to temporary and some- times permanent hearing loss, or deafness, over time. Hear- ing loss can be divided into two categories: conductive and sensorineural.

Conductive Hearing Loss

In conductive hearing loss, sound waves are not passed from the outer ear to the inner ear, usually because of a blockage or injury to the inner ear. For example, middle-ear infections may cause fluid to build up within the middle ear.

Sensorineural Hearing Loss

This problem may result from a birth defect, exposure to noise, growing older, and medication problems. One type of sensorineural hearing loss is tinnitus, a condition in which a ringing, buzzing, whistling, roaring, hissing, or other sound is heard in the ear in the absence of external sound. To prevent tinnitus, avoid loud music and wear earplugs in noisy environments and at loud concerts or sporting events. By limiting the length of time you are exposed to loud noise, you reduce the risk of permanent damage.