Supplemental Testing

Supplemental Testing is 3% of the COA exam: the short tests that answer questions a letter chart cannot. Each one has a specific job.

Order protects the results — color, stereo, and contrast come before dilation; tear-film tests come before anything touches or numbs the eye unless the protocol calls for anesthetic.

Congenital or acquired is the real question. Inherited red-green deficiency is X-linked and common (roughly 8% of males, about 0.5% of females), symmetric between the eyes, and stable for life. Acquired defects can appear at any age, are often asymmetric, and change over time; they point toward optic nerve or macular disease or drug toxicity. That is why each eye is tested separately.

Conditions decide the result — daylight-quality lighting (dim or yellow light manufactures failures), one eye at a time, with the patient's correction on. Hold the plates at about 75 cm and allow about 3 seconds per plate; long pauses let a patient work out figures they cannot actually see. Keep the book closed between uses so the colors do not fade.

Stereoacuity — the finest difference in depth the two eyes together can detect, measured in seconds of arc: the smaller the number, the better. The Titmus test uses polarized glasses; the fly is a coarse target, and the graded circles go down to 40 seconds of arc, generally treated as normal adult stereoacuity.

Random-dot tests — random-dot targets contain no outlines visible to one eye alone, so they can only be seen with genuine binocular vision. That makes them the more honest screen for young children and suspected suppression.

Why stereo matters — fine stereopsis requires both eyes aligned and working together, so a good result is indirect evidence of alignment.

Worth 4-dot — the patient wears red-green glasses (by convention, red over the right eye) and views four lights: one red, two green, one white.

Test at distance and near, and confirm which lens is over which eye before recording a side.

Pachymetry — central corneal thickness averages about 540–550 μm. Applanation tonometry assumes an average cornea, so thick corneas read falsely high and thin corneas falsely low, and thin corneas carry a higher glaucoma risk in their own right. For ultrasonic pachymetry, anesthetize the eye and touch the center of the cornea lightly with the probe perpendicular; a tilted probe reads falsely thick. Take several readings. Optical pachymeters avoid contact. Chart the pressure and the thickness as measured; adjusting the pressure for thickness is the physician's call.

Schirmer test — bend the strip at its notch and place the short end over the lower lid margin where the middle and outer thirds meet, clear of the cornea. The patient keeps the eyes closed or blinks normally, per the clinic's protocol, for 5 minutes; then read the wetting in millimeters from the notch. Without anesthetic the test measures basal plus reflex tearing; with anesthetic it approximates basal secretion. About 10 mm or less in 5 minutes without anesthetic is generally considered low. Always chart which version was done.

Tear break-up time (TBUT) — place a small amount of fluorescein, have the patient blink a few times, then keep the eyes open without blinking. Under cobalt blue light, time how long after the last blink the first dry spot appears; less than about 10 seconds suggests an unstable tear film. Too much dye lengthens the time and hides the problem.

Exophthalmometry — the Hertel instrument rests on the lateral orbital rims and reads how far each cornea sits in front of them, in millimeters. Record the base (the rim-to-rim setting) and reuse it at every visit, or the readings cannot be compared. Asymmetry of more than about 2 mm between the eyes, or change over time, matters most. Thyroid eye disease is the classic reason to measure.

Contrast sensitivity — real life is low-contrast. On the Pelli-Robson chart every letter is the same size and the contrast fades in groups of three; the score is the faintest group in which the patient reads at least two of the three letters. It reveals functional loss from cataract, glaucoma, or optic nerve disease that a high-contrast chart misses.

Glare testing — a brightness acuity tester compares acuity with and without a bright surrounding light. A cataract patient who reads 20/25 in a dark lane can lose several lines under glare, and documenting that loss supports the surgical decision.

Amsler grid — covers about 10° on every side of fixation, one eye at a time, with the reading correction on, at about 30 cm. The patient looks only at the central dot and reports wavy lines (distortion) or missing or gray areas (scotoma).

Be ready to match each test to its question, separate Ishihara's job from the D-15's, describe congenital color deficiency, explain seconds of arc and why random-dot tests need true binocular vision, interpret Worth 4-dot responses, state how corneal thickness biases applanation, give the Schirmer and TBUT cutoffs, and say what a Hertel exophthalmometer measures.