Because a visual acuity test is usually performed under normal daylight conditions, it does not indicate how well a person can see in low light. This distinction is important to make because “twilight vision” can be noticeably worse for some people with certain eye conditions. As a result, they may find it difficult to drive or perform other important tasks under low-light conditions. Decreased twilight vision (often referred to as “night myopia”) can be a problem for many young adults who have a slight shift toward nearsightedness. Older adults may also experience night myopia as a result of clouded eye lenses (cataracts), while others may have retinal eye diseases that cause decreased vision at lower light levels.
P.S. Twilight vision can be tested during a visual acuity test with a Snellen (E) eye chart by using filters that block out light at varying levels.