A striped pattern (grating) will appear at low contrast. Identify if the stripes are vertical or horizontal. Contrast decreases each round until you can't tell.
Contrast sensitivity measures your ability to distinguish an object from its background when the difference in luminance is small โ distinct from visual acuity (sharpness). It's critical for night driving, fog, and low-light sports, and tends to decline with age even when 20/20 acuity is preserved.
More vision tests: Sports Vision Test or Color Perception Test.