While many people feel uncomfortable driving at night, most of us don’t think about how well we are able to see during the evening. According to Optometry and Vision Science, a simple testing method has been developed to identify people who have decreased visual acuity (clarity or sharpness of vision) under these lower light conditions.
“Typically, eye chart visual acuity is measured at light levels that approximate daylight (photopic) vision conditions,” explains Anthony Adams, OD, PhD, Editor-in-Chief of Optometry and Vision Science, which is the official journal of the American Academy of Optometry. “However, twilight vision or vision at dusk (mesopic vision) can be noticeably worse for some people, especially for patients with eye problems.”
The Clinical Research
By using varying light filters, the visual acuity of 43 participants was tested at daylight level and during twilight conditions using three different light levels that mimicked various stages of twilight. Researchers then assessed how their vision was affected by low light levels and studied other factors like the normal increase in pupil size.
The study participants, healthy individuals with an average age of 25, had “normal” vision (about 20/20) in daylight. Researchers discovered that as the participants’ environment became progressively darker, visual acuity decreased from normal to almost three eye chart lines worse at the darkest level tested. The change in pupil size was unrelated to the change in visual acuity, while the “focus posture” of the eyes (accommodative error) had only a small effect.
Trouble Seeing In Low Light
Sometimes called “night myopia,” decreased twilight vision can be a major functional problem for many young adults and can cause them to have a slight shift toward myopia. According to All About Vision, nearsightedness, or myopia, is the most common refractive error of the eye. As adults age, people can also have poor twilight vision but for other reasons that have more to do with decreased clarity of the eyes’ contents, like the eye’s internal lens. Others may have retinal eye diseases that decrease vision at lower light levels.
Until now, there hasn’t been a standard approach to testing vision in low light. While there are continuous questions about the factors contributing to it, the new study provides a simple and reliable approach to testing twilight vision and reveals light levels are the major factor in a decrease in visual acuity. According to Jason S. Ng, OD, PhD of Southern California College of Optometry at Marshall B. Ketchum University in Fullerton, CA, further studies in older age groups could be an important way of testing or screening for various eye health issues, especially for patients with concerns around night vision.
Studies show that the health of macular pigment, a protective pigment found in the part of the retina responsible for high-definition vision, affects the quality of people’s sight, including how well they are able to see in low light conditions. EyePromise macular health vitamins like Screen Shield Pro have been proven to increase this natural protection and improve visual performance measures like clarity and ability to see in low light.