CHAPTER 2 Vision and Hearing

Vision and hearing problems are the “quiet debilitators.” Often defects in these two important senses are so subtle that they are unnoticed until educational or significant medical implications emerge. Because vision and hearing problems generally begin in a child’s critical years of development, early detection and diagnosis are vital so that medical treatment and rehabilitation can begin sooner, physical or behavioral complications can be avoided or minimized, and long-term educational implications can be eliminated or reduced. Such measures ensure that the child will have a fuller and more productive life.

Ideally, the first visual and hearing screening should occur when the newborn is in the nursery. Universal newborn hearing screening is becoming the standard so infants will receive early, optimal intervention for language development. Tests for the infant and very young child do not obtain acuities or thresholds; testing relies on elicitation of responses from various forms of stimuli. The younger the child, the more general the screening procedure.

Any nurse who works with infants and young children can play a major role in early detection of a vision or hearing deficit. The nurse has the opportunity to observe behavior, listen to parental concerns, and, in many instances, perform developmental, hearing, and vision screening. The school nurse is often the first person to observe and screen an older child with a vision and hearing problem.

Once the nurse suspects a vision or hearing problem, an appropriate referral should be initiated. Depending on the circumstances, the referral is made to the attending physician or one or more specialists, such as an ophthalmologist, optometrist, otolaryngologist, or audiologist.

Various vision and hearing problems occur in children and young adults. This chapter addresses the more common problems and presents major characteristics of vision and hearing development, a list of high-risk conditions that impair infants, screening methods, and certain testing procedures. Useful glossaries and acronyms of vision and hearing terms are listed at the end of their respective sections.

Information regarding vision, hearing, and brain development has been added to this chapter. Technology and research have prompted a new awareness of the importance of early vision and hearing deprivations. Torsten Wiesel and David Hubel won the Nobel Prize in 1981 for two very significant discoveries. They found that even with an intact brain, if an individual does not process visual experiences early in life, he/she will not be able to see due to the absence of cortical stimulation. They demonstrated that organization of the adult visual cortex is dependent on early visual experiences; and after that sensitive time period has passed, significant deficits occur in the visual cortex; e.g., cataracts prevent seeing visual experiences; therefore, if not removed early infant will be blind.

Other discoveries demonstrated that if words are not heard by age 10, the individual will never totally learn his/her native language as the brain cells will migrate to other functioning areas (Kotulak, 1996). The developing postnatal brain differs from that of an adult; thus, this period of early critical experiences is essential for brain development in the sensory systems.

Figures 2-1 to 2-4 illustrate the basic structures of the eye and ear and the pathways and mechanics that enable vision, hearing, and the understanding of a language.

FIGURE 2-1 Normal structure of the eye. A, Anterior view. B, Cross-sectional view.

FIGURE 2-2 Visual pathway.

FIGURE 2-3 Normal structures of the ear.

FIGURE 2-4 Auditory processing of sounds in the brain.

The cross-section depicts the lens in each eye, focusing light on the retina and inverting the image. Receptors in the retina convert the image into nerve impulses that travel along the optic nerve to the optic chiasm, where half of the nerves from each eye cross over to the other side of the brain, continuing on alternate pathways to the visual cortex. What is seen in the right half of the visual field is transmitted to the left hemisphere of the brain, and what is seen in the left half of the visual field is transmitted to the right hemisphere. Each hemisphere is aware of what the other perceives as visual information flows back and forth.

The visual cortex lies within the occipital lobes. Other visual association areas are located in various areas of the cerebral hemispheres; these areas interpret visual images. See Figures 1-1 and 1-2, pages 3-4.

Sound is perceived in both the left and right sides of the auditory cortex in the brain from impulses received by both ears. The left hemisphere translates sound impulses into meaning and is the language-processing center of the brain. The auditory cortex receives incoming impulses; the angular gyrus links vision to Wernicke’s area, whereas Wernicke’s area supplies the meanings of words, and Broca’s area controls the mechanics of speech.

REFRACTIVE ERRORS

ASTIGMATISM

I. Definition

A. Astigmatism is a refractive error in which light rays are refracted different at two or more points, because of the irregularity of the cornea, producing a distorted image. May occur along with myopia or hyperopia.

II. Etiology

A. Astigmatism may be caused by an irregularly shaped or defective curvature of the cornea or lens, which creates unequal refraction of incoming light rays in different meridians. This prevents the eye from focusing clearly on an image. Astigmatism may be congenital or acquired.

III. Signs, Symptoms, and History

Dependent on severity of refractive error in each eye:

A. Higher astigmatism.

1. Blurred vision.

2. Squinting; eye rubbing.

3. Tilting or turning of the head.

4. Reading material held close to eyes.

B. Lower astigmatism.

1. Tired eyes.

2. Blurred vision.

3. Frontal headache.

C. Mild astigmatism.

1. There may be no symptoms.

IV. Effects on Individual

A. Safety concerns; susceptibility to accidents because of blurry vision.

B. Difficulty with near and/or distance activities, such as close schoolwork and chalkboard activities, depending on associated visual error. Child may tire quickly with reading assignments and seem easily distracted.

C. May have same clinical manifestations as myopia.

V. Management/Treatment

A. Correction for refractive errors that creates a uniform surface (cornea or lens) through which light rays may pass, such as lenses (glasses or contacts). It is corrected with a combination of plus and minus lenses to fit the individual curvature of the astigmatic eye (Anshel, 2007).

B. Rescreen at appropriate intervals.

C. Be cautious of a child who does not like to wear the new glasses. Astigmatism corrections usually require an adaptation period. Check with prescribing doctor if doubt exists.

VI. Additional Information

A. Most people’s eyes are not perfectly symmetrical; thus, they may have small amounts of astigmatism. Astigmatism is common in infants. High astigmatism can result in amblyopia.

MYOPIA

I. Definition

A. Commonly called nearsightedness, myopia is the inability to see objects at distance. Myopia is a refractive error in which parallel light rays from a distant object focus in front of the retina, causing images at a distance from the individual to appear blurred. Figure 2-5 illustrates the distortion caused by myopia, as well as hyperopia and astigmatism, and corrections for each condition.

II. Etiology

A. Myopia may be caused by an elongated anterior-posterior diameter of the eyeball or a cornea curve that is too severe, thereby refracting the light rays too much. Heredity plays a role in myopia.

III. Signs, Symptoms, and History

A. Blurred distance vision.

B. Unusual posturing.

C. Squints at distant object to sharpen vision.

D. Rubs eyes frequently.

E. Headache, but rare.

F. Dizziness.

G. Nausea after close work, but rare.

H. Holds book close to face (severe or high myopia); however, this behavior is normal behavior between 4 and 7 years. It is also a first sign of a problem.

I. Depending on classroom seating, unable to see whiteboard or chalkboard or at home, television.

J. Fails distance vision testing.

IV. Effects on Individual

A. Difficulty participating in sports or playground activities.

B. Safety concerns; may walk into objects, inability to read road signs.

C. May miss whiteboard or chalkboard instructions if not sitting at front of classroom.

D. Academic performance may be affected if myopia severe or/and seating cannot be changed.

V. Management/Treatment

A. Correction, if indicated, with concave (minus) lens to focus rays on retina: either fitted glasses or contact lens may be used; or corneal surgery in older children to reduce corneal curvature (see Figure 2-5).

B. Surgery: laser techniques to reduce curvature of the cornea. These surgeries can be performed as early as 18 years, but typically should not be done before the eye has stopped growing.

C. Recheck periodically with and without prescribed glasses to see if error remains corrected.

VI. Additional Information

A. Growth produces visual changes, so child may need new eyeglasses every 1 or 2 years. Generally stabilizes around the mid-teen years.

FIGURE 2-5 Refractive errors displaying point of focus, distortion of globe, and lens correction. Arrow indicates point of focus, or fovea. Astigmatism could have both convex and concave surfaces and not necessarily flat.

HYPEROPIA

I. Definition

A. Commonly called farsightedness, hyperopia is the inability to see objects clearly at close range. Hyperopia, also termed hypermetropia, is a refractive error in which parallel light rays focus behind the retina, causing images close to the individual to appear blurred. In middle age, hyperopia is confused with presbyopia which is caused by the decreased elasticity of the crystalline lens.

II. Etiology

A. Hyperopia may be caused by insufficient length of the eyeball or by a lens that is too flat (unresponsive) to bend light rays adequately, thereby causing an image to focus beyond the retina, or by an inadequately curved cornea.

III. Signs, Symptoms, and History

A. Blurred vision at close range.

B. Tired eyes when focusing for prolonged periods of time.

C. Pain in the eyes.

D. Frontal headaches.

E. Eye strain after long periods of reading or writing.

F. Lines appear to run together while reading.

NOTE: Symptoms A to F intensified when individual is tired or ill.

G. Light sensitivity.

H. May fail visual screening.

I. Esotropia or an inward (medial) deviation of one or both eyes from parallelism.

J. Fails near vision testing.

IV. Effects on Individual

A. Schoolwork may suffer, and child may be unable to keep up with classmates.

B. Teachers may expect only poor academic achievement.

C. Student is more easily irritated because of constant eyestrain.

D. Student may be nervous during school visual tasks (e.g., reading, computer work).

E. Student may develop poor self-esteem if vision is affecting academic achievement or performance in playground activities.

V. Management/Treatment

A. Correction with use of convex (plus) lenses (glasses or contacts) to focus rays on retina (see Figure 2-5).

B. Correction may be necessary in children with only a moderate degree of hyperopia and no other symptoms or a strabismus.

C. Recheck periodically, with and without prescribed glasses, to determine whether error remains corrected.

VI. Additional Information

Most infants are hyperopic, and children continue to be so until they reach about 5 to 7 years, when normal development elongates the eyeball. These children can accommodate to objects at close range. If the child is truly hyperopic, the continual muscular effort of accommodation may cause eyestrain to result in strabismus (esotropia) or amblyopia. Hyperopia is measured in plus diopters rather than as a Snellen notation.

COLOR DISORDERS

COLOR DEFICIENCY/ABSENCE

I. Definition

A. Color deficiency or absence is the inability to distinguish between the primary colors red, green, and blue. In color deficiencies, photochemical receptors in the cones are diminished while in color absence, there is an actual lack of one or more of three receptors. Color vision is a function of central vision in the fovea cones of the eye. When stimulated by light, the cones transmit impulses to the brain. The cones facilitate discernment of color and detail while the rods are sensitive to movement and light; helps one adjust to darkness. Deficiencies or absences range from mild to severe. Color blindness, or the complete absence of all three photochemical receptors in the cones, is rare but limits vision to black, white, and gray shades.

II. Etiology

A. Color disorders are a defect inherited as an X-linked recessive trait that primarily affects the male population. The gene for color vision may not be faulty, but the gene that chemically triggers the color vision gene to function may be defective. Occasionally, a color disorder may be acquired from injury, disease (sickle cell anemia, diabetes), or certain drugs (antibiotics, chlorpromazine [Thorazine]); however, most incidences are about 4% hereditary. In any given classroom, about 4% of the students may have color disorders. Approximately one half the populations of a group of children are male; therefore, about 4% of a given class will be color-affected. Deficiencies/absences in the green photochemical receptors are the most common; blue receptors are the least common. Color disorders can affect many areas of life, including education, safety, and some occupational choices.

III. Signs, Symptoms, and History

A. Unable to discriminate colors, particularly reds and greens.

B. Difficulty learning primary colors.

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