The C Test uses a ring with a small gap, often called a Landolt C. The person identifies the direction of the gap as the symbol becomes smaller. It is a simple idea with useful applications.
A test based on orientation
Unlike a letter chart, the C symbol does not depend on alphabet knowledge. The gap may face up, down, left, right or a diagonal direction. Correctly locating that gap requires the eye to resolve fine detail.
What the result can tell you
A carefully administered test can estimate visual acuity under defined conditions. Screen size, viewing distance, lighting and whether glasses are worn all influence the result. An online version can be educational, but variations between devices prevent it from replacing a calibrated clinical examination.
Using the test responsibly
Test one eye at a time without pressing on the covered eye, keep the recommended distance and stop if you feel discomfort. A sudden reduction in vision, pain, flashes, a curtain-like shadow or new distortion requires prompt assessment by an eye-care professional.
A clear next step
Write down what you have noticed, when it began and which activities are affected. That simple record can make a professional conversation more focused and useful.