6.3 Sensory Examinations: Vision (Snellen/Ishihara) & Hearing (Audiometry)

6.3 Sensory Examinations: Vision (Snellen/Ishihara) & Hearing (Audiometry)

Sensory diagnostic evaluations for visual acuity, color discrimination, auditory thresholds, middle ear compliance, and ocular/auricular irrigations are vital clinical functions performed by the Certified Medical Assistant. Executing these procedures with rigorous adherence to standardized distances, lighting, temperatures, and anatomical alignment prevents diagnostic errors and protects patient safety.

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1. Visual Acuity & Color Vision Testing Modalities

Visual assessments evaluate the refractive and neurological functionality of the optical system. Refractive errors include myopia (nearsightedness; light focuses anterior to the retina), hyperopia (farsightedness; light focuses posterior to the retina), astigmatism (irregular corneal or lenticular curvature causing blurred focus), and presbyopia (age-related loss of crystalline lens elasticity and ciliary muscle accommodation, typically developing after age 40).

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|                                 SUMMARY OF SENSORY ASSESSMENTS                                   |
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| 1. SNELLEN CHART   | Distance visual acuity at 20 feet; OD, OS, OU; normal is 20/20.            |
| 2. JAEGER CARD     | Near visual acuity at 14–16 inches; J1–J14; normal is J2 (presbyopia).      |
| 3. ISHIHARA PLATES | Red-green color deficiency; 30 inches, 45° angle, 3-second limit.          |
| 4. WEBER TEST      | 512 Hz fork on vertex/midline; conductive lateralizes to affected ear.      |
| 5. RINNE TEST      | Fork on mastoid vs 1" from meatus; normal is AC > BC (AC is double BC).     |
| 6. AUDIOMETRY      | Pure tones 250–8000 Hz, 0–110 dB; threshold softest heard 50% of time.     |
| 7. TYMPANOMETRY    | Eardrum compliance & middle ear pressure; Type A (normal), Type B (effusion).|
| 8. EAR IRRIGATION  | Water warmed to 98.6°F (37°C); pull pinna up/back (adult) or down/back (<3).|
| 9. EYE IRRIGATION  | Flush inner to outer canthus; 15–30 min continuous flush for chemical burns.|
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Distance Visual Acuity: The Snellen Eye Chart

• Testing Distance & Setup: The Snellen eye chart is mounted on a wall in a well-illuminated room with the 20/20 line positioned at the patient's eye level. A clearly visible floor marker is placed exactly 20 feet (6 meters) from the chart.
• Testing Sequence:
  • Test OD (Oculus Dexter - Right Eye) first while occluding the left eye.
  • Test OS (Oculus Sinister - Left Eye) second while occluding the right eye.
  • Test OU (Oculi Uterque / Oculus Uterque - Both Eyes) last with both eyes uncovered.
• Corrective Lenses: If the patient wears corrective eyeglasses or contact lenses for distance vision, test with lenses on first, then repeat without lenses if ordered by the provider. Document clearly (e.g., OD: 20/20 with correction; OD: 20/50 without correction). Note: Patients must not wear reading-only glasses during distance Snellen testing.
• Occluder Protocol: The patient holds a clean plastic eye occluder over the non-tested eye. Critical Instruction: The patient must keep both eyes open behind the occluder. Squinting, peeking around the occluder, or squeezing the non-tested eye closed causes sympathetic squinting and pupillary changes that produce artificially altered visual acuity.
• Reading Protocol & Scoring: Instruct the patient to read from the top line downward. A line is considered passed if the patient reads it with no more than 2 missed letters. Record the visual acuity as the fraction corresponding to the smallest line successfully read, noting errors (e.g., 20/30 -1 indicates the 20/30 line was read with 1 error; 20/25 +2 indicates the 20/25 line was passed plus 2 letters on the 20/20 line).
• Interpretation of Snellen Fractions:
  • Numerator (20): The fixed distance (20 feet) between the patient and the chart.
  • Denominator: The distance at which a person with standard normal vision can read that specific line.
  • Example: 20/40 vision indicates that the patient can read at 20 feet what a person with normal 20/20 vision can read from a distance of 40 feet.
  • Legal Blindness: Defined as corrected visual acuity of $\le 20/200$ in the better-seeing eye, or a visual field diameter of $\le 20$ degrees.
• Specialized Distance Charts:
  • Snellen E Chart (Tumbling E): Designed for illiterate, non-English speaking, or young pediatric patients (ages 3–5). The patient points fingers in the direction the open prongs of the "E" point (up, down, left, right).
  • Lea Symbols / Picture Charts: Utilizes standardized geometric symbols (circle, square, house, apple) for pediatric visual screening.
  • Allen Picture Cards: Utilizes recognizable silhouettes (car, horse, tree, bird) for toddlers.

Near Visual Acuity: The Jaeger Chart

• Purpose: Evaluates near vision and screens for presbyopia and hyperopia.
• Equipment & Testing Distance: A handheld card containing short paragraphs of text formatted in ascending font sizes, graded from J1 (smallest/finest print) to J14 (largest print). The card is held exactly 14 to 16 inches (35 to 40 cm) from the patient's eyes in good lighting.
• Protocol: Test OD, OS, and OU, with and without corrective reading glasses. The patient reads the smallest paragraph possible without moving the card closer or farther away. J2 represents standard normal near visual acuity (equivalent to 20/20 at 14 inches).

Color Vision Discrimination: Ishihara Polychromatic Plates

• Purpose: Screens for congenital red-green color deficiency (protanopia and deuteranopia), an X-linked recessive genetic trait affecting approximately 8% of males and 0.5% of females, as well as acquired optic nerve pathologies.
• Testing Protocol: Standard booklet containing 14, 24, or 38 polychromatic plates. Each plate consists of a circular array of dots in varying sizes, colors, and brightness forming hidden numerals or winding paths against a contrasting background.
• Administration: Administer in natural daylight or standardized glare-free fluorescent lighting. The plate is held 30 inches (75 cm) away from the patient at a 45-degree angle to the line of vision. The patient must identify the hidden number within 3 seconds. If illiterate or pediatric, the patient traces the winding line using a cotton-tipped swab (never bare fingers, as skin oils degrade the pigments). Plate 1 is a universal control plate readable by all patients.

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2. Hearing Acuity & Audiometric Testing

Hearing assessments evaluate acoustic conduction through the external/middle ear and sensorineural transduction in the cochlea and auditory nerve (Cranial Nerve VIII).

Classification of Hearing Loss

• Conductive Hearing Loss: Caused by physical interference with sound wave conduction through the external auditory canal, tympanic membrane, or ossicular chain (malleus, incus, stapes). Causes: impacted cerumen, otitis media with effusion, perforated tympanic membrane, otosclerosis, foreign body obstruction.
• Sensorineural Hearing Loss: Caused by permanent damage to the sensory hair cells of the organ of Corti in the cochlea, the auditory nerve (CN VIII), or the auditory processing pathways in the brain. Causes: presbycusis (age-related high-frequency sensorineural loss), chronic loud noise exposure, ototoxic medications (aminoglycosides like gentamicin, high-dose aspirin, loop diuretics, cisplatin), Meniere's disease, and acoustic neuroma.
• Mixed Hearing Loss: Concurrent conductive and sensorineural deficits.

Gross Hearing Assessment: The Whisper Test

• Technique: The medical assistant stands 2 feet (arms-length / 0.6 m) directly behind the patient to eliminate visual lip-reading cues. The patient occludes the non-tested ear and rubs the tragus in small circular motions. The CMA exhales fully and whispers a series of 3 random numbers/letters (e.g., "4-K-2"). The patient repeats them. Repeating $\ge 50%$ correctly represents passing.

Diagnostic Tuning Fork Tests (512 Hz)

A 512 Hz tuning fork is the clinical standard because it falls squarely within the human speech frequency band (500–3,000 Hz) without producing distracting somatosensory bone vibrations.

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|                             DIAGNOSTIC TUNING FORK DIFFERENTIATION                              |
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| 1. WEBER TEST (Midline Vertex / Forehead):                                                       |
|    - Normal: Sound heard equally in both ears (no lateralization).                               |
|    - Conductive Loss: Sound lateralizes to the AFFECTED (impaired) ear.                          |
|    - Sensorineural Loss: Sound lateralizes to the UNAFFECTED (normal) ear.                       |
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| 2. RINNE TEST (Mastoid Bone [BC] vs. 1 Inch from Canal Meatus [AC]):                             |
|    - Normal / Positive Rinne: AC > BC (Air Conduction duration is twice Bone Conduction).        |
|    - Conductive Loss / Negative Rinne: BC >= AC (Bone Conduction heard equal to or longer than AC).|
|    - Sensorineural Loss: AC > BC (both reduced, but AC remains longer than BC).                  |
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• The Weber Test (Bone Conduction Lateralization):
  • Procedure: Activate the tuning fork by striking the prongs against the heel of the hand. Place the vibrating stem firmly against the midline of the skull on the vertex of the skull or the center of the forehead.
  • Ask the Patient: "Do you hear the sound equally in both ears, or is it louder in one ear?"
  • Clinical Interpretation: In a conductive hearing loss, sound lateralizes to the affected (abnormal) ear because ambient room noise is blocked by the conduction defect, allowing bone vibrations to be perceived more loudly. In a sensorineural hearing loss, sound lateralizes to the unaffected (normal) ear because the damaged cochlea/nerve in the abnormal ear cannot transduce the signal.
• The Rinne Test (Air Conduction vs. Bone Conduction):
  • Procedure: Strike the fork. Place the vibrating stem firmly against the mastoid process behind the ear (testing Bone Conduction - BC). Instruct the patient to signal immediately when the sound stops. The instant the patient signals, quickly move the vibrating tines 1 inch (2.5 cm) in front of the external auditory meatus (testing Air Conduction - AC). Ask if the patient can still hear the tone.
  • Normal / Positive Rinne ($+Rinne$): Air Conduction is twice as long as Bone Conduction ($AC > BC$, or $AC = 2 \times BC$).
  • Conductive Loss / Negative Rinne ($-Rinne$): Bone Conduction is greater than or equal to Air Conduction ($BC \ge AC$). The patient does not hear the tone when moved in front of the meatus, indicating middle/external ear pathology.

Pure-Tone Audiometry & Tympanometry

• Pure-Tone Audiometry: Uses an electronic audiometer in a quiet soundproof room. Tests individual frequencies from 250 to 8,000 Hz across sound intensities from 0 to 110 decibels (dB) through calibrated headphones (Red = Right, Blue = Left). The hearing threshold is the softest sound level in decibels at which the patient detects the tone 50% of the time. Normal hearing threshold is 0 to 25 dB.
• Tympanometry: Objective assessment of tympanic membrane compliance and middle ear pressure. A soft probe tip creates an airtight seal in the ear canal while changing air pressure and transmitting a continuous tone.
  • Type A Curve (Normal): Symmetrical mountain-shaped peak at normal atmospheric pressure ($0\text{ daPa}$), reflecting normal membrane mobility.
  • Type B Curve (Flat / Non-Mobile): No compliance peak, indicative of middle ear effusion (serous otitis media), hemotympanum, or tympanic perforation.
  • Type C Curve (Negative Pressure Peak): Compliance peak shifted to significant negative pressure ($<-100\text{ daPa}$), indicating Eustachian tube dysfunction or early acute otitis media.

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3. Ear & Eye Irrigation and Instillation Protocols

Ear Irrigation (Aural Lavage)

• Indications: Removal of impacted cerumen, non-vegetable foreign objects, or purulent exudate.
• Absolute Contraindications: Perforated tympanic membrane, presence of ventilating tympanostomy tubes (PE tubes), history of myringotomy or ear reconstruction, active severe otitis externa, or vegetable/organic foreign bodies (e.g., beans, peas, corn, which absorb moisture, swell rapidly, and cause severe canal impaction and necrosis).
• Irrigation Solution & Temperature Control: Utilize warm sterile water, normal saline, or dilute hydrogen peroxide. The solution MUST be warmed to normal body temperature: $98.6°\text{F} (37.0°\text{C})$. Critical Danger: Cold or hot water stimulates the lateral semicircular canal of the inner ear, triggering the caloric reflex, which induces immediate, violent vertigo, nystagmus, severe nausea, and vomiting.
• Procedure & Canal Alignment:
  • Patient sits upright, holding an emesis basin firmly against the neck beneath the earlobe with a protective drape.
  • Adults and Children $\ge 3$ Years: Pull the pinna (auricle) upward and backward to straighten the S-shaped external auditory canal.
  • Infants and Toddlers $< 3$ Years: Pull the pinna downward and backward.
  • Direct the irrigating nozzle gently toward the superior/posterosuperior wall of the canal. Fluid flows along the canal roof, sweeps behind the cerumen impaction, and flushes it outward into the basin. NEVER direct the stream directly at the center of the tympanic membrane, as the hydraulic force can rupture the eardrum.

Eye Irrigation (Ocular Lavage)

• Indications: Chemical burns (acids/alkalis), foreign body debris, irritants, or purulent secretions.
• Ocular Chemical Burn Emergency: Alkaline chemical exposure (e.g., lye, bleach, ammonia, drain cleaner) causes liquefactive necrosis and penetrates ocular tissues rapidly. Irrigation must begin immediately and continue for at least 15 to 30 minutes (using 1 to 2 liters of sterile normal saline or Lactated Ringer's) until the conjunctival pH neutralizes to 7.0 to 7.4 on litmus/pH paper.
• Irrigation Protocol: Patient is supine with head tilted toward the affected eye (preventing runoff from entering the unaffected eye or lacrimal punctum). Retract eyelids gently. Direct the gentle stream from the inner canthus (nasal/medial aspect) to the outer canthus (temporal/lateral aspect) across the lower conjunctival sac. A Morgan Lens (a specialized scleral lens connected to IV tubing) may be inserted for continuous, hands-free corneal and conjunctival lavage.

Eye & Ear Medication Instillations

• Ophthalmic Drops: Patient tilts head back and looks up. Retract lower eyelid to form a conjunctival pocket. Instill prescribed drops into the lower conjunctival sac (never directly onto the cornea). Apply gentle pressure over the nasolacrimal duct (inner canthus) for 1 to 2 minutes to prevent systemic medication absorption.
• Otic Drops: Warm bottle between palms. Position patient with affected ear facing upward. Straighten canal (up/back for $\ge 3$ yrs; down/back for $<3$ yrs). Instill drops along the canal wall. Press the tragus gently several times to facilitate distribution. Patient remains in position for 3 to 5 minutes.

Sensory Examination Modalities & Diagnostic Values

Speech and Word Recognition Testing

Pure-tone audiometry establishes the softest tone a patient can detect at each frequency, but detecting a tone is not the same as understanding speech. Speech audiometry adds two measures, and the AAMA content outline names both.

The SRT functions as an internal validity check: when it disagrees with the pure-tone average by much more than 10 dB, the test is unreliable and is repeated — a discrepancy suggests inattention, misunderstanding of the task, or a non-organic (functional) hearing loss.

The word recognition score is the measure that distinguishes types of loss. In conductive loss, sound is simply attenuated on its way in, so once it is made loud enough the patient understands it well and word recognition remains high. In sensorineural loss, the cochlea or auditory nerve distorts the signal, so making speech louder does not fully restore intelligibility and word recognition falls disproportionately. This is the physiologic reason patients with presbycusis say "I can hear you, I just can't understand you," and why shouting at them does not help.

Medical assistant responsibilities. Confirm by otoscopy that the canal is free of cerumen impaction, which produces an artifactual conductive loss. Test in a quiet room or booth. Position the patient so they cannot see your face or the audiometer display, because lip-reading and visual cues invalidate the score. Present the standardized word list at the prescribed level without emphasis or repetition. Document the ear tested, the presentation level, the SRT, and the word recognition percentage, and report the results to the provider without interpreting them.