Sometimes you get ready for bed and turn off the light, but you can't sleep. You open your eyes and you can't see a thing. It takes a few minutes for your vision to return. This process, ''dark adaptation,'' causes people to see even when there's almost no light.
A person with a healthy set of eyes probably takes night vision - and the role of the biochemical, physical and neural mechanisms - for granted. Let's have a look at how this works. The retina is a layer of cells at the back of the eye. The section of the retina opposite 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 rods have the capacity to function even in low light conditions but those cells are absent from the fovea. As you may know, the details and colors we see are sensed by the cones, and rod cells are sensitive to light and detect movement.
Considering these facts, if you want to see something in the dark, like a faint star in the night sky, instead of looking directly at it, try to use your peripheral vision. 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.
Your pupils also dilate when it's dark. It requires approximately one minute for your pupil to completely dilate; however, it takes approximately 30 minutes for your eyes to achieve full light sensitivity.
Dark adaptation occurs if you leave a bright area and enter a dim one, for example, walking inside after being out in the sun. It'll always take a few moments for your eyes to adjust to regular indoor light, but if you go back outside, that dark adaptation will vanish in a moment.
This is actually one reason behind why so many people have trouble driving at night. If you look right at the ''brights'' of opposing traffic, you may find yourself momentarily unable to see, until that car passes and your eyes readjust to the night light. A good way to prevent this sort of temporary blindness is to avoid looking right at headlights, and learn to try to allow peripheral vision to guide you.
There are a number of things that may cause decreased night vision, including: not getting enough Vitamin A in your diet, cataracts, glaucoma, or some other visual obstruction. Should you begin to notice that you experience problems with seeing at night, book an appointment with one of our eye doctors who will be able to shed some light on the issue.