3.1 Visual Assessment Overview

3.1 Visual Assessment Overview

Visual acuity (VA) is the measure of the eye's ability to resolve fine spatial detail, and it is the most frequently performed test in any ophthalmology clinic. On the Certified Ophthalmic Assistant (COA) exam administered by the International Joint Commission on Allied Health Personnel in Ophthalmology (IJCAHPO), Visual Assessment carries roughly 7% of the 200 scaled multiple-choice questions under the content outline effective August 1, 2025. The exam is 180 minutes; you have about 54 seconds per question, so VA notation and endpoints must be automatic.

Visual acuity notation

VA is written as a fraction. The numerator is the test distance; the denominator is the distance at which a person with normal sight could read that same line. So 20/40 means the patient at 20 feet reads what a normal eye reads at 40 feet. A smaller denominator is better vision; 20/20 is the standard reference, and many adults achieve 20/15.

Recording order and abbreviations

Always chart VA in a fixed sequence so the chart is unambiguous: OD (right eye) first, then OS (left eye), then OU (both eyes). Note the correction state with each value:

• sc (sine correctio) = without correction
• cc (cum correctio) = with correction (glasses or contacts)
• ph = with the pinhole occluder

For example, "VAsc OD 20/60, OS 20/40; ph OD 20/25" tells the doctor the right eye improves with pinhole, suggesting an uncorrected refractive error rather than disease.

Standard testing distance

The Snellen chart is calibrated for 20 feet (6 meters), which approximates optical infinity and relaxes accommodation. Many lanes are shorter and use a mirror system or a projected/LCD chart so the optical path still equals 20 feet. If a true 20-foot lane is unavailable, the chart can be scaled, but the recorded distance must reflect the actual optical path.

Notation for very low vision

When the patient cannot read the top letter at 20 feet, you walk the chart toward the patient and record the new distance, e.g. 10/200 or 5/200. If no chart letter is seen, move down the low-vision ladder, in this exact order from better to worse:

1. Count fingers (CF) at a stated distance, e.g. "CF at 3 ft"
2. Hand motion (HM) at a stated distance
3. Light perception with projection (LP with projection) — patient localizes direction of light
4. Light perception (LP) — sees light but cannot localize
5. No light perception (NLP) — total blindness, a medicolegally critical finding

Legal-blindness endpoint

Legal blindness in the US is best-corrected VA of 20/200 or worse in the better eye, or a visual field of 20 degrees or less. A high-yield trap: pinhole and automated-refraction acuities are NOT used to certify legal blindness because they estimate potential, not true best-corrected vision. The COA records the data; the ophthalmologist certifies the disability.

Why the procedure matters

Visual acuity is the clinic's chief complaint converted into a number, and almost every later decision depends on it. An inflated or sloppily recorded acuity can mask a worsening cataract, hide early macular disease, or make a stable eye look like it is deteriorating. Because the doctor often sees only your recorded value, the COA's measurement effectively becomes the medicolegal record of how the patient could see on that date. Reproducibility is therefore as important as the raw number: the same patient, same chart, same distance, and same correction should yield the same result on repeat testing.

The COA must also understand what acuity does not tell you. Snellen acuity measures only central, high-contrast resolution under ideal illumination. It says nothing about peripheral vision, contrast under glare, color discrimination, or binocular function, all of which require separate tests covered later in this chapter. A patient can read 20/20 and still be functionally disabled by glare, field loss, or diplopia. Treat the acuity line as the opening measurement, not the whole assessment, and always pair it with the patient's stated complaint when you decide what to flag for the physician.

Metric and Snellen equivalents

Many clinics, charts, and international questions use the metric (6-meter) system. The conversions are direct: 20/20 equals 6/6, 20/40 equals 6/12, 20/200 equals 6/60, and 20/15 equals 6/4.5. The logMAR scale used by the ETDRS chart assigns 0.0 to 20/20, with each step of three letters worth 0.1 logMAR; lower logMAR is better vision. Knowing these equivalents prevents a charting error when a patient's prior record uses a different notation than your lane.

The ETDRS chart deserves special mention because research studies and many surgical clinics use it as the gold standard. Unlike the Snellen chart, which has an uneven number of letters per line and inconsistent spacing, the ETDRS chart has exactly five letters per line with proportional spacing and a geometric size progression. This lets technicians score acuity letter by letter, which is far more sensitive to small changes than the Snellen chart and is why it is preferred for tracking macular disease or drug-trial endpoints.

For COA purposes, know that ETDRS is more precise and reproducible but slower, while Snellen is faster and clinically standard.