Introduction to Eye and Ear Assessment

The medical assistant is responsible for performing a vari­ety of assessments and procedures that involve the eye and the ear. An understanding of the structure and func­tion of the eye and the ear is essential to mastering skill in these areas.

A visual acuity test is usually part of the routine physi­cal examination. This test is a screening test to detect defi­ciencies in vision.

The medical assistant may be responsible for assessing color vision with the use of specially prepared colored plates. As a result of this testing, color blindness can be de­tected. Color blindness is an inability to distinguish cer­tain colors; the most common problem is with the colors red and green. This is particularly significant if the patient is involved in an activity that relies on the ability to dis­tinguish colors, such as electronics and interior decorating.

Hearing tests may also be part of the routine physical examination. During contact with the patient, the medical assistant should be alert to signs that indicate the patient might be having difficulty hearing what is being said. A whispered voice or a ticking watch held next to the pa­tient's ear can be a screening test for hearing acuity. The use of tuning forks or an audiometer provides a more ac­curate determination of hearing acuity. Anaudiometer is an instrument that emits sound waves at various frequen­cies. The patient is instructed to indicate when a sound at a given frequency can be heard.

The medical assistant is responsible for performing or teaching the patient to perform eye and ear irrigations and instillations.Irrigation is washing a body canal with a flowing solution.Instillation is dropping a liquid into a body cavity. Eye and ear irrigations and instillations should be performed using the important principles of medical asepsis outlined in Chapter 2.

Structure of the Eye

Figure. The internal structure of the eye. (From Applegate EJ: The anatomy and physiology learning system, ed 2, Philadelphia, 2000, Saunders.)

The eye has three layers. The outer layer is the sclera, which is composed of tough, white fibrous connec­tive tissue. The front part of the sclera is modified to form a transparent covering over the colored part of the eye; this covering is the cornea.

The middle layer of the eye is the choroid, which is com­posed of many blood vessels and is highly pigmented. The blood vessels nourish the other layers of the eye, and the pigment works to absorb stray light rays. The front part of the choroid is specialized into the ciliary body, the sus­pensory ligaments, and the iris. The ciliary body contains muscles that control the shape of the lens. The function of the suspensory ligaments is to suspend the lens in place. The lens is responsible for focusing the light rays on the retina. The colored part of the eye is the iris, which controls the size of the pupil. The pupil is the opening in the eye that permits the entrance of light rays.

The third and innermost layer of the eye is the retina. Light rays come to a focus on the retina and are subse­quently transmitted to the brain, by way of the optic nerve, to be interpreted.

The anterior chamber is the area between the cornea and the iris, and the posterior chamber is the area between the iris and the lens. Both chambers are filled with a substance known as the aqueous humor. A transparent jellylike mate­rial, known as vitreous humor, fills the eyeball between the lens and the retina. Its function is to help maintain the shape of the eyeball.

The conjunctiva is a membrane that lines the eyelids and covers the front of the eye, except the cornea. The con­junctiva covering the sclera is transparent except for some capillaries, which allows the white sclera to show through.