Every once in a while, I get a friend who sends me an article saying, “Playing with the lights off for too long can cause ‘eye cancer’! I get articles like this asking me to confirm whether it is true or not. The article often mentions something like “Macula is a very important part of human eyes, and direct light from cell phones in the dark for more than 30 minutes will cause macular degeneration in the eyes, resulting in rapid deterioration of vision.” Every time I was quite puzzled how this 30-minute figure was actually derived. But there doesn’t seem to be any definitive evidence that playing with a cell phone before bed causes macular degeneration. But it does have some effects on the eyes. First, there is a temporary invisibility or difficulty in seeing. The main manifestation is that after playing cell phone for a long time in the dark, one eye can see something, but the other eye cannot see or see, and it takes some time to slowly adapt to the dark environment. This is mainly related to the habit of using cell phones. At night with the phone, many people are used to lying on their side with one eye to see, the other eye is closed, or may be covered by a pillow or quilt. At this time, if you suddenly turn off the phone screen light, in the dark, you may find that the eye that looked at the phone before may not see anything, but the other eye can see. In fact, this is the dark adaptation of the human eye. Usually when we walk from a bright place to a dark place, we will also have this feeling that our eyes can’t see anything, and need to adapt for a while to gradually see things in the dark. The human eye has two types of photoreceptor cells: cone cells and rod cells. In a bright environment, light is sensed by the optic cone cells, which can distinguish colors, so we can distinguish different colors in bright places. Under bright light stimulation, the retinal cone cells in the retina can immediately go to work, so from dark to light, our eyes may feel the light blinding for just a moment at first, but immediately we can see the object, this process is called bright adaptation, which lasts about 1 minute. And in the dark environment, it is the optic rod cells that play a role, this is because they can produce the retinal red matter which is sensitive to low light and greatly improve the light sensitivity of human eyes. It takes about 5 minutes in the dark to produce 60% of the retinas, and about 30 minutes to produce all of them, so the process of dark adaptation takes about 30-40 minutes to complete. Optic rod cells do not have the ability to recognize the color of objects, so when you look at something in the dark, it is all one color. When using a cell phone at night with the lights off, if one eye is looking, after the screen light is turned off, it is the same as this eye needs to make dark adaptation to see things clearly, while the other eye is already in a dark environment due to closed eyes or being blocked, and has already completed dark adaptation, so it will produce the phenomenon that one eye can see, but the other eye cannot see or cannot see, and it takes some time before they can all see. Second, the development of refractive error, especially for adolescents whose eyes are still developing, is also caused by the habit of looking at the phone with one eye as mentioned earlier. As a result of using one eye for a long time, it may cause the eye to look too close and use the adjustment, so that the myopia of the eye develops faster, resulting in the refractive error of both eyes, i.e., the difference in prescription is too large. Third, may cause dry eye, visual fatigue long time eye, staring at the screen, the human eye involuntarily will blink less, so it is easy to dry eyes, soreness and other dry eye and visual fatigue symptoms. Fourth, cause glaucoma attacks This may also be the most serious kind of harm. In the case of dark light, the pupil will become larger, and for some people who have a shallow anterior chamber angle, it may induce the closure of the angle and a sharp rise in intraocular pressure, causing an attack of acute angle-closure glaucoma. Therefore, it is best not to play cell phones before going to bed, but, just as we all know that smoking is harmful to health, but still many people are smoking, simple and brutal request not to look at the phone before going to bed, or quite difficult to do. Then if you must play, please pay attention to the following two points: First, pay attention to the light many people suggest that the phone into night mode, because they think the phone screen is too bright, and the contrast between the environment is too large, it will make the eyes cause fatigue. But I do not agree too much. I think the phone screen or to keep the normal brightness, it is best to open a reading light / night light, which makes the phone screen and the environment is not too big contrast on. Because the phone brightness is too dark, not only may cause glaucoma attacks, and will increase visual fatigue. Second, both eyes to look at the same time try not to play sideways, if you must play sideways, take care not to compress the eyeball, to avoid the appearance of always be a single-eyed look at the phone state. It is best to look at the phone with both eyes at about the same distance, and the eyes are not too close to the screen. Of course, the best way is still to quit the phone before bed.