Looking at screens for too long can cause eyestrain, but eyestrain existed long before screens. (Driving long distances is another cause, the Mayo Clinic notes.) Eyestrain may involve fatigue of the tiny muscles in and around our eyes, and people who get eyestrain may experience discomfort that includes headaches, blurry vision, watering of the eyes, and sensitivity to light.
There’s a rumor that the blue light from smartphones (or other screens) can ruin your vision, perhaps even leading to blindness, but it’s not backed up by evidence. “The amount of light coming from a computer has never been demonstrated to cause any eye disease,” the American Academy of Opththalmology states in an article on their website recommending against blue-light-blocking glasses. There is research that finds blue light can damage cells in certain lab conditions, but those conditions are very different from what happens in the actual cells of our retina.
Unfortunately, there are companies citing research like this to sell their blue-light-blocking glasses or screen overlays, but they aren’t selling a solution to a real problem. This happened to me recently after getting an eye test for glasses for all day looking at screens. The prescription is actually for vision correction (that's all) but guess what, the optometrist also sells glasses, and somehow I got hoodwinked into adding blue light lens coatings "to prevent eyestrain". This adds a considerable amount to the price. In future too I'll take my prescription and get quotes for glasses (including online) as the whole business seems to be a bit of a scam. I paid double the rate of a GP for the tests and got zero report back.
And regarding affecting sleep, the recommendation is to just have screens an inch or two further away - my screens are at 85 cm which is way further than the recommended 63 cm. In other words we should be better educated about how to use our eyes, and not necessarily just be sold blue light filter coatings on lenses.
See What Happens to Your Eyes When You Stare at Screens All Day
We spend a lot of time staring at screens. There’s the small screen in our pocket, the big screen we watch our shows on, and the medium screen that many of us stare into for eight hours a day to help pay for those other screens. Are all of these screens ruining our eyes?