As the speculum is introduced farther into the canal in a downward and forward direction, the tympanic membrane is visualized. The tympanic membrane should appear as an intact, ovoid, semitransparent, pearly gray membrane at the end of the canal. The lower four fifths of the tympanic membrane is called the pars tensa; the upper fifth, the pars flaccida. The handle of the malleus should be seen near the center of the pars tensa. From the lower end of the handle, there is frequently a bright triangular cone of light reflected from the pars tensa. This is called the light reflex, which is directed anteroinferiorly. The pars flaccida, the short process of the malleus, and the anterior and posterior folds should be identified. A normal tympanic membrane is pictured in Figure 11-17A, and the important landmarks are identified in Figure 11-17B.
The presence or absence of the light reflex should not be considered indicative of either normality or disease. The sensitivity of the light reflex for indicating disease is low. There are as many normal tympanic membranes without a light reflex as there are abnormal membranes with a light reflex.
Describe the color, integrity, transparency, position, and landmarks of the tympanic membrane.
Healthy tympanic membranes are usually pearly gray. Diseased tympanic membranes may be dull and become red or yellow. Is the eardrum injected? Injection refers to the dilatation of blood vessels, making them more apparent. The blood vessels should be visible only around the perimeter of the membrane. Dense, white plaques on the tympanic membrane may be caused by tympanosclerosis, which is caused by deposition of hyaline material and calcification within the layers of the tympanic membrane. This condition is commonly (in 50% to 60% of cases) secondary to the insertion of ventilation tubes. The classic horseshoe shape of tympanoscle-rosis is seen in the tympanic membrane shown in Figure 11-18. Despite the size of these lesions, they usually do not impair hearing and are rarely of clinical importance. If the lesion extends into the middle ear, however, conductive deafness may result.
Is the tympanic membrane bulging or retracted? Bulging of the membrane may indicate fluid or pus in the middle ear. No bubbles or fluid should be seen behind the tympanic membrane in the middle ear. A tympanic membrane becomes retracted when intratympanic cavity pressures are reduced: for example, when the eustachian tube is obstructed. Figure 11-19 depicts a ''retraction pocket'' just above the lateral process of the malleus, a condition known as attic retraction. On occasion, the entire tympanic membrane may become retracted
onto the ossicles of the middle ear. The ossicles may become eroded, with the development of a conductive hearing loss.
If the tympanic membrane is perforated, describe the characteristics. Perforation of the tympanic membrane can occur after trauma or infection.
The normal position of the tympanic membrane is oblique to the external canal. The superior margin is closer to the examiner's eye. This is frequently better seen in infants than in adults.
In the normal ear, the handle of the malleus attached to the tympanic membrane is the primary landmark. Frequently, the long process of the incus may be seen posterior to the malleus. The chorda tympani nerve, which supplies innervation to the anterior two thirds of the tongue and stimulates taste there, is frequently visible in the upper posterior quadrant;it passes horizontally across the middle ear behind the tympanic membrane between the long process of the incus and the handle of the malleus. Keratin patches appear as multiple, discrete white patches on the tympanic membrane of all normal membranes; if illumination is not sufficient, however, they may not be visualized. In the presence of a retracted tympanic membrane, the malleus is seen in sharp outline.
There are many differences in the color, shape, and contour of the tympanic membrane, which can be recognized only with experience.
After examining the right ear, examine the left ear by holding the otoscope in the left hand and straightening the canal with the right hand.
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