Some nights, you lie in your bed, all ready to dream the night away with the lights off, but you can't sleep. You open your eyes and you can't see a thing. You need several moments to get used to the dark and then objects in the room begin to re-appear. We call this ''dark adaptation'' and it's what lets our eyes get used to the dark.
Many people don't know that night vision is dependent upon the cooperation of physical, neural and biochemical mechanisms. So how do your eyes operate in the dark? Firstly, let's examine the eye and its anatomy. The retina is a layer of cells at the back of the eye. The area of the retina across from the pupil which produces sharp focused vision is called the fovea. The retina comprises cone cells and rod cells, named for their respective shapes. The rod cells are able to function more efficiently than cone cells in low light conditions but they are not found in the fovea. As you may know, the cones enable us to see color and detail, while rod cells are sensitive to light.
So, if you want to see something in the dark, you'll be better off if you look at something off to the side of it. You want to maximize the use of the rod cells in low light, and avoid relying on your cone-rich fovea, even though it seems counter-intuitive to look away from the object you want to see.
Another process your eye undergoes is pupil dilation. It takes fewer than sixty seconds for the pupil to completely dilate; however, dark adaptation keeps improving your ability to see for the next half hour and, as everyone has experienced, during this time, your ability to see in the dark will increase remarkably.
Dark adaptation occurs when you first enter a dark cinema from a bright area and struggle to find somewhere to sit. After a while, your eyes adapt to the situation and see better. This same thing occurs when you're looking at the stars in the sky. Initially, you probably won't be able to actually see that many. If you keep looking, your eyes will dark adapt and the stars will gradually appear. Even though it takes several moments to adapt to the dark, you'll quickly be able to re-adapt to exposure to bright light, but if you go back into the darker setting, your eyes will need time to re-adjust again.
This is one reason behind why many people don't like to drive when it's dark. If you look directly at the lights of opposing traffic, you are briefly blinded, until you pass them and you readjust to the night light. To prevent this, don't look right at headlights, and learn to use peripheral vision in those situations.
There are a number of conditions that could potentially cause trouble with night vision. Here are some possibilities: a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. If you notice problems with night vision, schedule an appointment with one of our eye care professionals who will be able to shed some light on the issue.