What are the cause of eye strain during computer usage?

It happens because your eyes follow the same path over and over. And it can get worse the longer you continue the movement. When you work at a computer, your eyes have to focus and refocus all the time. They move back and forth as you read. You may have to look down at papers and then back up to type. Your eyes react to changing images on the screen to create so your brain can process what you’re seeing. All these jobs require a lot of effort from your eye muscles. And to make things worse, unlike a book or piece of paper, the screen adds contrast, flicker, and glare.

You’re more likely to have problems if you already have eye trouble, if you need glasses but don't have them, or if you wear the wrong prescription for computer use.

Computer work gets harder as you age and the lenses in your eyes becomes less flexible. Somewhere around age 40, your ability to focus on near and far objects will start to go away. Your eye doctor will call this condition presbyopia.

By putting your camera into shutter speed priority. this way camera will automatically adjust the iso and the aperture in accordance with the environment.