The ear drum, technically called the tympanic membrane, is a thin, oval sheet of tissue that serves as the boundary between the outer ear canal and the middle ear space. It is fundamental to the process of hearing. The primary role of the tympanic membrane is to capture sound waves traveling down the ear canal and convert them into mechanical vibrations. These vibrations are then transferred directly to the tiny bones of the middle ear, initiating the sound transmission pathway to the inner ear.
Structure and Location
The tympanic membrane is positioned at the end of the external ear canal, where it forms the lateral wall of the middle ear. It sits obliquely, forming an angle of approximately 55 degrees with the floor of the ear canal. This slight tilt contributes to its efficiency in capturing sound waves.
The structure is composed of three distinct layers. The outermost layer is continuous with the skin of the ear canal, while the innermost layer is a mucous membrane that lines the middle ear cavity. Sandwiched between these is a middle fibrous layer, which provides the membrane’s structural integrity and tensile strength.
The membrane is divided into two parts: the pars tensa and the pars flaccida. The pars tensa is the larger, lower section that contains the robust fibrous layer, making it taut and highly vibratory. The smaller pars flaccida lacks this strong fibrous layer, making it looser.
Describing the Healthy Ear Drum
A healthy tympanic membrane presents a characteristic visual appearance when examined by a healthcare professional using an otoscope. Its color is typically described as translucent or pearly gray. The membrane is also extremely thin, allowing structures of the middle ear to be faintly visible through it.
The healthy ear drum is slightly cone-shaped, concave inward toward the middle ear space. This conical shape is maintained by the handle of the malleus, the first of the three middle ear bones. The handle appears as a pale streak running down to the membrane’s most depressed point, known as the umbo.
Another distinctive feature is the “cone of light,” a triangular reflection of the otoscope’s light source. Because of the membrane’s concave shape, the light reflects back in a specific pattern, usually visible in the anterior-inferior quadrant. The presence and clarity of this cone of light confirm the membrane’s proper resting position.
Visual Signs of Common Issues
The visual appearance of the ear drum changes noticeably when common medical conditions affect the middle ear. Acute infection, such as acute otitis media, causes the membrane to become inflamed, resulting in a color shift from pearly gray to distinctly red. This intense redness is due to the increased blood flow to the area.
Pressure changes within the middle ear space also dramatically alter the membrane’s shape. Bulging (convex outward) of the drum is a sign of positive pressure, typically caused by the accumulation of pus or fluid behind it during an active infection. Conversely, an excessively concave or retracted appearance suggests negative pressure in the middle ear, often due to a blocked Eustachian tube.
When non-infected fluid is present in the middle ear, the translucent membrane may take on a yellow-brown or amber hue, a condition sometimes referred to as “glue ear.” In some cases, air bubbles or a visible fluid line (air-fluid level) can be seen behind the membrane, confirming the presence of middle ear fluid. A tear or hole, known as a perforation, is a direct visual sign of a burst eardrum, which may appear as a dark spot or opening in the membrane.