3.3 Scenario Practice for Visual Assessment

3.3 Scenario Practice for Visual Assessment

Scenario questions give you a patient and a complaint and ask which test to run or how to read the result. Read each stem in this fixed order: which eye, what correction state, which chart and distance, and what is the abnormal finding the stem is steering you toward.

Color vision screening

Color vision is most commonly screened with Ishihara pseudoisochromatic plates, which detect red-green deficiencies (protan and deutan defects). The patient, tested one eye at a time at about 30 inches in good (ideally daylight) illumination, names the number hidden in the dot pattern. Inability to read the plates suggests a red-green defect, which is the most common inherited color deficiency and affects roughly 8% of males and 0.5% of females. The Farnsworth D-15 is used to grade severity and to detect blue-yellow (tritan) defects, which are more often acquired (e.g., from optic-nerve or retinal disease).

Worked scenario: monocular vision loss

A 58-year-old reports painless, sudden blurring in the left eye since yesterday. You measure VAcc OD 20/20, OS 20/200, no pinhole improvement OS. The correct COA action is to complete accurate documentation, screen the pupils for a relative afferent pupillary defect (RAPD) with the swinging-flashlight test, and alert the ophthalmologist promptly — not to keep re-testing or to dilate on your own. Sudden monocular loss with an RAPD suggests optic-nerve or retinal pathology that may be time-critical.

Worked scenario: "my Snellen is fine but I can't drive at night"

A patient with 20/25 Snellen acuity complains of glare and poor night vision. Snellen uses high-contrast black letters on white and can miss functional deficits. The appropriate tests are contrast sensitivity (e.g., Pelli-Robson chart) and glare/brightness-acuity testing. Reduced contrast sensitivity with normal Snellen acuity is classic for early cataract and helps justify surgery.

Worked scenario: distortion

A patient reports wavy, distorted central vision. The screening tool is the Amsler grid, held at the reading distance with reading correction, one eye at a time. Reported wavy lines (metamorphopsia) or a missing central patch (central scotoma) point to macular disease such as age-related macular degeneration and warrant referral.

Across every scenario, the pattern is the same: match the symptom to the correct test, record the result in standard notation, and recognize the handful of findings — NLP, a new RAPD, sudden monocular loss, leukocoria — that require prompt physician notification rather than repeated technician testing.

A six-step reading method for scenario items

Most candidates miss scenario questions not because they lack knowledge but because they answer before they have fully parsed the stem. Use a deliberate method on every item. First, name the patient population (infant, child, literate adult, presbyope) because it dictates which chart is even allowed. Second, identify the complaint or trigger — distortion, glare, color confusion, sudden loss — because the complaint points to the specific test. Third, pin down the eye and correction state the stem gives you. Fourth, decide the test and distance that matches. Fifth, predict the expected finding and how you would chart it.

Sixth, ask whether the finding is routine or physician-alert. Working in that order, the tempting distractor that ignores the population or the complaint becomes easy to reject.

Worked scenario: the uncooperative toddler

A two-year-old will not name letters or match symbols. A weak candidate picks "record unable to test." The stronger answer steps down the pediatric ladder: assess fixation behavior using the CSM convention — is fixation central, steady, and maintained through a blink in each eye? Asymmetry, such as steady fixation in one eye but not the other, suggests reduced acuity or strabismus in the weaker eye. Documenting CSM for each eye gives the physician usable data even when no chart acuity is obtainable, which is exactly the judgment the exam expects.

Worked scenario: the patient who improves too much

A patient's acuity jumps from 20/80 to 20/20 the moment you hand them the occluder, faster than they could plausibly read. The cue is that the patient may be squinting or peeking, both of which create a pinhole-like effect and falsify the result. The correct move is to re-test with a proper opaque occluder, instruct the patient to keep both eyes open and relaxed, and re-record. Recognizing that an implausibly good jump signals a technique artifact, not a real result, is a recurring scenario theme.

Worked scenario: confrontation visual fields

A patient reports bumping into objects on one side. Before any formal perimetry, the COA can perform a confrontation visual field screen: sit facing the patient about one meter away, have them cover one eye and fixate on your nose, then present fingers in each of the four quadrants of peripheral vision and ask the patient to count them. A consistently missed quadrant suggests a field defect — a missed temporal field in both eyes, for instance, raises concern for a chiasmal lesion, while a homonymous loss on one side points behind the chiasm.

Confrontation fields are a screen only; an abnormal result is documented and the physician decides whether automated perimetry is warranted. This scenario reinforces the chapter's core lesson: pick the test that matches the complaint, document the finding precisely, and escalate rather than diagnose.