Visual Assessment

Visual acuity is the vital sign of ophthalmology — measured before anything else is done to the eye: before drops, before pressure, before bright lights.

Snellen notation — 20/40 means the patient reads at 20 feet what a standard eye reads at 40. A 20/20 optotype spans 5 minutes of arc with 1-minute detail. Metric charts use 6 meters: 6/6 = 20/20. Record each eye separately, with correction (cc) and without (sc), always right eye first, partial lines with plus-minus notation (20/40+2).

Pinhole — if acuity improves through a pinhole, uncorrected refractive error is the likely cause; no improvement suggests media opacity or retinal/neural disease. Check it whenever acuity is reduced.

Near acuity — tested at 40 cm (16 in) with the near card and the patient's reading correction; recorded in Jaeger, point, or reduced Snellen. A presbyope without their add will test falsely poor — note missing correction.

When the chart can't be read — walk the patient closer and record the true distance (5/400), then descend the scale in order: count fingers with distance (CF @ 3 ft), hand motion (HM), light perception with projection, light perception (LP), no light perception (NLP).

Preliterate children — Lea symbols, HOTV with a matching card, Allen pictures. The child points to the match; speed and play win cooperation. Infants: fix-and-follow per eye, recorded as CSM (central, steady, maintained), plus how strongly the child objects to covering each eye.

Adults who don't read English letters — tumbling E or Landolt C: the patient signals the direction of the opening, preserving a true optotype measurement.

Amblyopia and crowding — amblyopic eyes read isolated letters better than full lines. Test with lines or crowding bars, or the deficit hides.

Latent nystagmus — full occlusion makes it worse; fog the fellow eye with a high plus lens instead of covering it.

ETDRS / logMAR charts — five letters per line, uniform geometric steps: the standard for research and low vision, where 'lines lost' must mean the same thing everywhere on the chart.

Glare testing — a cataract patient can read 20/25 in a dark lane and be disabled in sunlight. Brightness acuity testing documents the real-world loss and often justifies surgery.

Occlusion done right — a solid occluder or cupped palm resting on the orbital rim. Spread fingers invite peeking; pressure on the globe blurs the covered eye for its own turn.

Consistent conditions — chart luminance, room lighting, and testing distance must match visit to visit, or trend lines mean nothing. Short lanes use calibrated mirrors or distance-scaled charts.

Timing matters — acuity (and pupils) come before drops. After dilation, accommodation is impaired and near acuity reads falsely poor.

What was actually tested — habitual correction, newest Rx, or unaided? The chart must say (cc/sc), because the same eye can honestly produce three different numbers.

Inconsistent performance — when claimed vision doesn't match observed behavior, chart objective observations neutrally and inform the physician. Sorting out functional vision loss is the doctor's job; accusations are nobody's.