Vision & Eye Test Glossary
Every term used across OpticQuiz, in plain English — each linked to the test or guide where it lives.
- Visual acuity
- The smallest high-contrast detail your eye can resolve — “how sharp is your vision.” Measured with an eye chart. Acuity test · guide
- Snellen fraction (20/20)
- The eye-chart notation for acuity. 20/20 means you read at 20 feet what a normal eye reads at 20 feet — normal, not maximum. What 20/20 means
- logMAR
- A precise acuity scale used clinically and in research, where 0.0 equals 20/20 and lower numbers are sharper. The metric cousin of the Snellen fraction.
- Contrast sensitivity
- Your ability to detect faint differences in lightness — “how faint can it be,” the axis that matters in fog and dim light. Contrast test · guide
- Just-noticeable difference (JND)
- The smallest change in a stimulus you can reliably detect — for color, the smallest hue gap you can still tell apart. Hue test
- Adaptive staircase
- A testing method that makes each trial easier or harder based on your last answer, homing in efficiently on your threshold. Used in the contrast, hue, saturation, and vernier tests.
- Threshold
- The level at which you can just barely perform a task — the faintest color, smallest offset, or highest flicker you can still detect. The number most perception tests are chasing.
- Ishihara plate
- A dot-pattern image hiding a number visible to normal color vision but not to a matching color deficiency. The classic color-blindness screen. Color test · how they work
- Confusion line
- A set of colors that a specific color deficiency can’t tell apart. Ishihara plates and the D-15 test are built along these lines. D-15 test
- Protanopia / protanomaly
- Red-channel color deficiency — reds look dimmer and are confused with greens and browns. “-opia” is the strong form, “-anomaly” the mild. Color blindness explained
- Deuteranopia / deuteranomaly
- Green-channel color deficiency — the most common type of color blindness, with red-green confusions. guide
- Tritanopia / tritanomaly
- Blue-yellow (blue-channel) color deficiency — rare, not sex-linked, often acquired. Blues look greenish, yellows wash out.
- Anomaloscope / Rayleigh match
- The clinical gold-standard color test: you mix red and green light to match a yellow reference. Where you settle reveals your red-green balance. Anomaloscope
- Hyperacuity / vernier acuity
- The ability to detect misalignment between lines at a scale finer than a single cone — one of the sharpest things human vision does. Vernier test
- Critical flicker fusion (CFF)
- The frequency at which a flickering light stops looking like it’s blinking and appears steady — a measure of temporal vision. Flicker test
- Amsler grid
- A grid used to check central vision for wavy, blurry, or missing areas linked to macular problems such as AMD. Amsler grid
- Metamorphopsia
- Distortion of vision that makes straight lines look wavy or bent — a key sign the Amsler grid is designed to catch.
- Astigmatism
- A cornea or lens shaped more like a rugby ball than a sphere, focusing one orientation better than another and blurring vision. Astigmatism test · home test
- Blind spot / optic disc
- The receptor-free patch where the optic nerve exits each eye, so images there aren’t seen. Everyone has one. Blind spot mapper · guide
- Dominant eye
- The eye your brain favors for aiming and judging direction, like handedness. Dominant eye test · guide
- Achromatopsia
- Total or near-total color blindness — seeing little or no color — usually with light sensitivity and reduced sharpness. Extremely rare.
- Saturation
- How vivid or “colorful” a hue is versus gray. The saturation test finds the faintest color you can still detect. Saturation test
- Visual reaction time
- How fast you perceive a visual change and respond — perception plus motor delay, measured in milliseconds. Reaction test