Eye test — Landolt C
Calibrate your screen, measure your distance and identify the C-shaped gap with arrow keys or touch. Free, with all responses processed in your browser.
Screen calibration
A visual-acuity self-check, not a medical eye exam. It cannot diagnose eye disease, determine a prescription or confirm that your vision is healthy.
Free, without an account or camera. Calibration and responses stay in this page’s memory and are cleared when you leave or reload. Eye results are not sent to analytics.
How it works
- An isolated Landolt C has an outer diameter five times its stroke and gap width. Size is calculated from your ruler calibration and measured viewing distance, not an assumed screen DPI.
- Each size has 5 independently randomized symbols. At least 4 correct answers advance to a smaller size; the first unsuccessful size ends the session. Sizes change in 0.1 logMAR steps, starting at decimal acuity 0.1.
Where is the gap?
Press an arrow key or select the matching direction. Release the key between answers. If you cannot tell, choose “Not sure”. Escape stops the session.
Calibrate the screen and confirm your distance to begin.
Assumptions and limitations
This simplified four-direction procedure has not been clinically validated and is not an ISO-compliant or licensing test. Guessing, screen quality, lighting, calibration and viewing distance affect results. It checks recognition of an isolated high-contrast shape only; it does not test your full visual field, eye health or reading vision. Concerns about vision need a professional eye exam.
Sources
- Michael Bach — FrACT: calibration and visual-acuity principles Sources reviewed: 2026-10-24
- National Eye Institute — comprehensive eye exams Sources reviewed: 2026-10-24
