Vision, Hearing, Allergy and Pulmonary Function Tests

Visual Acuity and Color Perception Screening

In the outpatient setting, the medical assistant routinely conducts visual acuity screenings under provider supervision during rooming or routine examinations. Distance visual acuity is most commonly assessed using a standard Snellen chart. The test is conducted with the patient standing or sitting exactly 20 feet away from the chart. The medical assistant instructs the patient to keep both eyes open throughout the procedure while using an opaque occluder to cover one eye at a time. Testing is typically performed on the right eye (OD) first, followed by the left eye (OS), and finally both eyes together (OU). If the patient wears corrective lenses for distance vision, the medical assistant tests and records their visual acuity with the lenses on first, unless the provider specifically instructs otherwise.

The results of a Snellen test are expressed as a fraction. The numerator represents the distance the patient stands from the chart, which is standard at 20 feet. The denominator represents the distance at which an individual with normal vision can read that specific line of characters. A patient successfully passes a line on the Snellen chart if they correctly identify more than half of the characters displayed on that line. For preliterate pediatric patients or non-English-speaking patients who may struggle with standard Latin letters, the medical assistant uses an alternative screening tool, such as the Tumbling E chart or the Landolt C chart.

Screening for near visual acuity assesses the patient's ability to read material close at hand, helping to detect conditions such as hyperopia and presbyopia. The medical assistant conducts this screening using a handheld card, such as a Jaeger card or a Rosenbaum pocket vision screener. The patient holds the test card 14 to 16 inches away from their eyes, similar to the natural distance one might hold a book or a smartphone. Each eye is tested individually and then both eyes together, documenting the findings accurately for the provider's review.

Color vision screening identifies inherited or acquired color vision deficiencies, particularly red-green color vision deficiencies. The medical assistant administers the Ishihara test by presenting test plates approximately 30 inches (75 cm) from the patient's eyes. The plates must be held perpendicular to the patient's line of sight and viewed under natural daylight or standardized illumination to avoid distorted color perception. The medical assistant allows the patient approximately 3 seconds to identify the number or trace the pattern present on each plate before documenting the responses.