It's happened to all of us; you get prepared for bed, and you turn the lights off, but you can't sleep. You open your eyes and you can't see anything. After a few moments you are able to distinguish between the objects in the room and the darkness around you. This process, ''dark adaptation,'' causes people to see even when it's really dark.
Night vision involves a number of biochemical, physical and neural mechanisms – for granted. But how does this work? The retina is a layer of cells at the back of the eye. The portion of the retina across from the pupil that is responsible for sharp focused vision is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rods are able to function even in low light conditions. Those cells are not found in the fovea. What's the difference between these two cell types? In short, cones contribute to color vision, while rod cells help us visualize black and white, and are light sensitive and detect movement.
So, if attempting to make out an object in the dark, like the dresser in your darkened room, instead of focusing right on it, try to look just beside it. By looking to the side, you take advantage of the rods, which work better in the dark.
Another process your eye undergoes is pupil dilation. It requires less than a minute for your pupil to completely dilate but it takes approximately 30-45 minutes for your vision to fully adapt.
You'll experience dark adaptation when you first enter a dark cinema from a bright lobby and struggle to find a seat. But soon enough, your eyes get used to the dark and before you know it, you can see. This same thing occurs when you're looking at the stars in the sky. Initially, you won't see many. Keep looking; while you dark adapt, millions of stars will become visible. It takes a few noticeable moments until you begin to adjust to normal indoor light. If you go back into the brightness, that dark adaptation will disappear in a moment.
This explains one reason behind why a lot people prefer not to drive at night. When you look at the ''brights'' of a car heading toward you, you may find yourself briefly unable to see, until you pass them and you once again adjust to the night light. To prevent this, don't look directly at headlights, and learn to use peripheral vision in those situations.
There are several things that could contribute to inability to see at night, including: diet-related vitamin deficiencies, cataracts, glaucoma, or some other visual obstruction. Should you begin to detect issues with night vision, call to make an appointment with one of our eye care professionals who will be able to shed some light on why this is happening.