The Special Senses - Ailments: what can go wrong with the special senses

---

Most problems that afflict the special senses are the result of normal aging. As people grow older, their lacrimal glands become less active. The eyes become dry and are more prone to infection and irritation. The muscles of the iris also become less efficient, and the lens tends to lose its crystal clarity. Both of these conditions cause less light to reach the retina, thereby reducing vision.

The ears are affected by few problems during childhood and adult life (except for ear inflammations or infections). However, after the age of sixty, the organ of Corti begins gradually to deteriorate and the ability to hear high tones and human speech decreases.

Smell and taste, the chemical senses, usually stay sharp throughout childhood and adult life. They gradually begin to decrease when a person reaches middle age because of a loss in the number of chemoreceptor cells. During life, impairment of smell and taste are usually the result of a nasal cavity inflammation (due to a cold, an allergy, or smoking) or a head injury. More serious infections in the nasal or oral cavity, such as oral candidiasis (yeast infection of the mucous membranes of the oral cavity), can obviously impair smell and taste.

The following are just a few of the disorders or diseases that can afflict some of the special senses.

Astigmatism

Astigmatism is a condition brought about by an uneven curvature of the cornea. As a consequence, some light rays entering the eye focus on the retina while others focus in front or behind it. The result is an indistinct or slightly out-of-focus image. Some cases of astigmatism are caused by problems in the lens. Minor variations in the curvature of the lens can result in minor degrees of astigmatism. In these cases, the cornea is usually normal in shape.

Astigmatism is a condition that may be present at birth. It may also be acquired if something is distorting the cornea. The upper eyelid resting on the eyeball, trauma or scarring to the cornea, tumors in the eyelid, or a developing condition in which the cornea thins and becomes cone shaped can all cause distortion. Diabetes can also play a role. High blood sugar levels can cause changes in the shape of the lens, resulting in astigmatism.

The main symptom of astigmatism is blurring. People with the condition can also experience headaches and eyestrain.

Astigmatism can generally be corrected by the use of cylindrical lenses, which can be in eyeglasses or contact lenses. The lenses are shaped to counteract the shape of the sections of the cornea that are causing the difficulty. In 1997, the U.S. Food and Drug Administration (FDA) approved laser treatment of astigmatism.

Cataracts

A cataract is a cloudiness in the normally transparent crystalline lens of the eye. This cloudiness can cause a decrease in vision and may lead to eventual blindness. Because cataracts are so common in the elderly, they are thought to be a normal part of the aging process. Of those people who are seventy years of age or older, at least 70 percent are affected by cataracts.

As people age, the lens hardens and changes shape less easily. The materials making up the lens also tend to degenerate. Changes in the proteins, water content, enzymes, and other chemicals of the lens are some of the reasons for the formation of a cataract. Some medical studies have determined that smoking, high alcohol intake, and a diet high in fat all increase the likelihood of cataract formation.

Common symptoms of cataracts include poor central vision, changes in color perception, increased glare from lights, poor vision in sunlight, and the painless onset of blurry or fuzzy vision. If the cataract forms in the area of the lens directly behind the pupil, vision may be significantly impaired. If it occurs on the outer edge or edges of a lens, vision loss is less of a problem.

When a cataract causes only minor visual changes, no treatment may be necessary. When it causes severe vision problems, surgery is the only treatment option. Cataract surgery, in which the lens is removed and a replacement or artificial lens is inserted, is the most frequently performed surgery in the United States. It generally improves vision in over 90 percent of those who undergo the procedure.

Conjunctivitis

Conjunctivitis, commonly known as pinkeye, is an inflammation of the conjunctiva that is usually the result of an infection (viral or bacterial) or an allergic reaction. It is an extremely common eye problem because the conjunctiva is continually exposed to microorganisms and environmental agents that can cause infections or allergic reactions. If caused by an infection, conjunctivitis is extremely contagious and can be easily transmitted to others during close physical contact.

Conjunctivitis caused by a viral infection (such as a cold) is marked by mild to severe discomfort in one or both eyes; redness in the eye or eyes; swelling of the eyelids; and a watery, yellow, or green discharge. Symptoms of bacterial conjunctivitis include redness, swelling, a puslike discharge, and crusty eyelids upon awakening. Conjunctivitis caused by wind, smoke, dust, pollen, or grass has symptoms ranging from itching and redness to a mucus discharge.

In most cases, warm compresses applied to the affected eye several times a day may help to reduce discomfort. In cases caused by a bacterial infection, an antibiotic eye ointment or eye drops may be prescribed. For conjunctivitis caused by an allergic reaction, cool compresses may be applied to the affected eye. Antihistamine drugs and eye drops may also be prescribed.

If treated properly, viral or bacterial conjunctivitis usually clears in ten to fourteen days. Conjunctivitis caused by an allergic reaction should clear up once the allergen (substance causing the allergic reaction) is removed.

Farsightedness

Farsightedness, known formally as hyperopia, is a condition of the eye where incoming rays of light reach the retina before they converge to form a focused image. While objects far away may be seen clearly, objects close up cannot. Babies are generally born farsighted, but this normally decreases with age as the eye grows.

Light waves from close objects tend to scatter. In order to focus those light waves precisely on the retina, the lens must bulge or become convex. In farsightedness, the lens is flatter than needed for the length of the eyeball. In other words, the eyeball is too short for the curvature of the lens, and the image of a nearby object is focused behind the retina.

People who are farsighted can see far objects clearly because light waves from distant objects approach the eye as parallel rays. The lens does not change its relatively flat shape in order to focus those rays on the retina.

There is no way to prevent farsightedness. Individuals with low to moderate farsightedness can achieve full vision by wearing corrective convex lenses (either eyeglasses or contact lenses). At the beginning of the twenty-first century, surgery to correct farsightedness had not yet been perfected or approved.

Glaucoma

Glaucoma is a serious vision disorder caused by a buildup of aqueous humor, which is prevented for some reason from properly draining. The excessive amount of fluid causes pressure to build up. The high pressure distorts the shape of the optic nerve and destroys the nerve. Destroyed nerve cells result in blind spots in places where the image from the retina is not being transmitted to the brain.

Following cataracts, glaucoma is the second leading cause of blindness in the United States. Over 2 million people in the country have glaucoma. Some 80,000 of those are legally blind as a result. Glaucoma is the most frequent cause of blindness in African Americans. There are many underlying causes and forms of glaucoma, but most causes of the disorder are not known.

In the most common form of glaucoma, the field of vision is lost over time. Usually the condition starts with a loss of the peripheral (side) vision so that the person does not realize he or she is losing sight until it is too late for treatment.

If treated early, the condition can be controlled with drugs (typically given as eye drops) that either increase the outflow of aqueous humor or decrease its production. Laser surgery or microsurgery to open up drainage canals can be effective in increasing the outflow of aqueous humor. Although the surgeries are successful, the effects often last less than a year.

There is some evidence that marijuana lowers the pressure caused by excess aqueous humor. However, marijuana has serious side effects and contains carcinogens (cancer-causing substances). The U.S. Food and Drug Administration and the National Institutes of Health are currently supporting medical research into marijuana and its possible use as a treatment for glaucoma.

Meniere's disease

Meniere's disease is a condition characterized by recurring vertigo or dizziness, hearing loss, and tinnitus (a buzzing or ringing sound in the ears). The disease is named for French physician Prosper Meniere, who first described the illness in 1861. An estimated 3 to 5 million people in the United States are afflicted with the condition. Meniere's disease usually starts between the ages of twenty and fifty, and it affects men and women equally. In about 85 percent of the cases, only one ear is affected.

The disease is an abnormality in the inner ear, specifically within the fluid-filled semicircular canals. A change in the fluid volume within the canals or a swelling of the canals is thought to result in symptoms characteristic of the disease. The cause of Meniere's disease is unknown.

In addition to the symptoms listed above, a person suffering from the disease may feel pain or pressure in the affected ear. Symptoms can appear suddenly and last up to several hours. They can occur as often as daily or as infrequently as once a year. Attacks of severe vertigo can force the sufferer to have to sit or lie down. Headache, nausea, vomiting, or diarrhea may accompany the attack.

There is no cure for Meniere's disease. Certain symptoms of the disease, such as vertigo, nausea, and vomiting, can be controlled with a variety of medications that are either taken orally or injected by needle. If the vertigo attacks are frequent and severe, surgery may be required.

The most common surgical procedure is the insertion of a shunt or small tube to drain some of the fluid from the canal. Unfortunately, this is not a permanent cure in all cases. In another surgical procedure, the nerves responsible for transmitting nerve impulses related to balance are cut. The distorted impulses causing dizziness then no longer reach the brain. This procedure permanently cures the majority of cases, but there is a slight risk that hearing or facial muscle control will be affected.

Nearsightedness

Nearsightedness, known formally as myopia, is the condition of the eye where incoming rays of light are bent too much and converge to form a focused image in front of the retina. While objects close to the eye may be seen clearly, distant objects appear blurred or fuzzy. Nearsightedness affects about 30 percent of the population in the United States.

Light waves from distant objects approach the eye as parallel rays. Normally, the lens does not change its relatively flat shape in order to focus those rays on the retina. In nearsightedness, the lens is thicker and more convex than needed for the length of the eyeball. In other words, the eyeball is too long (oblong instead of the normal almost spherical shape) for the curvature of the lens, and the image of a distant object is focused in front of the retina.

People who are nearsighted can see close objects clearly because light waves from those objects tend to scatter or spread out. The already convex shape of the lens helps to focus those rays on the retina.

Nearsightedness is considered to be primarily a hereditary disorder, meaning that it runs in families. However, some medical researchers believe that it results from a combination of genetic and environmental factors. The tendency toward being nearsighted may be inherited, but it may actually be brought about by factors such as close work, stress, and eye strain.

People who are nearsighted can (but not always) achieve full vision by wearing corrective concave lenses (either eyeglasses or contact lenses). Another possible treatment for nearsightedness is refractive eye surgery. In most surgical procedures, either a laser is used to vaporize small amounts of tissue from the cornea's surface (thereby flattening it) or a knife is used to cut a circular flap on the cornea, then a laser is used to change the shape of the inner layers of the cornea underneath. Depending on a person's degree of nearsightedness and other factors, refractive surgery can make permanent improvements.

Otitis media

Otitis media is an infection of the middle ear space behind the eardrum. By the age of three, almost 85 percent of all children will have had otitis media at least once. Babies and children between the ages of six months and six years are most likely to develop this type of infection. The most usual times of the year for otitis media to strike are in winter and early spring.

Otitis media is an important problem because it often results in fluid accumulation within the middle ear. The fluid can last for weeks or months, and it can cause significant hearing impairment. When hearing impairment occurs in a young child, it may interfere with the development of normal speech.

Because the middle ear is connected to the throat by the eustachian tube, an infection in the throat may easily reach the middle ear. In fact, most cases of otitis media occur during a bacterial infection of the upper respiratory tract.

Symptoms of otitis media include fever, ear pain, and problems with hearing. When significant fluid is present in the middle ear, pain may increase when a person lies down. Pressure from increased fluid buildup may also perforate or rupture the eardrum, causing bloody fluid or greenish-yellow pus to drip from the ear.

Antibiotics are the treatment of choice for ear infections. The type of drug depends on the type of bacteria causing the infection. Special nose drops, decongestants, or antihistamines may also be prescribed to improve the functioning of the eustachian tube. In rare cases, a procedure to drain the middle ear of pus may be performed.