Contrast sensitivity is the ability to see a range of low-contrast images in real-world settings. The contrast sensitivity test is different from standard acuity, which tests patients using only black-on-white, high-contrast letters. Unlike visual acuity, contrast sensitivity can determine how well a patient may be able to perceive low-contrast images, such as a shadowy sidewalk curb under a streetlight or a toolbox sitting on the floor of a dimly lit garage. Contrast sensitivity is a more sensitive measure of vision compared to acuity and can be used to detect and evaluate many eye conditions. It is also a very useful test for evaluating patients who participate in highly vision-intensive activities, such as athletes, pilots or police officers. The US Food and Drug Administration now requires contrast sensitivity testing in the clinical trials of new surgical technologies used to correct vision.