You wake suddenly, in the middle of the night, or maybe you’re looking for a light switch or door handle or phone in a room with the lights off. We’ve all found ourselves in the dark before. Gradually, the things in the room begin become visible. This process, ”dark adaptation,” allows us to adjust to the dark.
In order for night vision and dark adaptation to work, several physiological, neurological and biochemical mechanisms have to take place behind the scenes. Let’s have a closer look at how your eye actually operates in these conditions. Every eye takes in various forms of light using two kinds of cells: cones and rods, at the back of the eye; or, to be precise, on the retina. Together they form the sensory layer. This is the part that gives your eye the ability to pick up light and color. These cells are spread throughout your retina, with the exception of the small area known as the fovea, where there are only cone cells. That part is necessary for detailed sight, such as when reading. What’s the difference between rods and cones? In short, cones enable us to perceive color and detail, while the rods are sensitive to light and detect movement.
Let’s put this all together. Imagine struggling to focus on something in the dark, like a faint star in a dark sky, it’s more efficient to focus on something right next to it. That way, you’re avoiding the use of the fovea, which only has cells that are less sensitive to low light.
In addition to this, the pupils, the black circles in the middle of your eyes, dilate when it’s dark. Your pupil grows to it its largest diameter within a minute but it takes approximately 30 minutes for the eye to achieve full light sensitivity.
Dark adaptation occurs when you go from a very bright place to a darker one for example, when coming inside after being out in the sun. It’ll always take a few moments until your eyes fully adapt to normal indoor light. If you walk back out outside, those changes will be lost in a moment.
This explains one reason behind why a lot people have difficulty driving their cars at night. When you look right at the lights of opposing traffic, you are momentarily blinded, until that car is gone and your eyes readjust to the night light. To prevent this, don’t look directly at the car’s lights, and learn to use peripheral vision to observe oncoming traffic at night.
There are numerous conditions that could potentially cause trouble with night vision, including: a nutritional deficiency, macular degeneration, cataracts, glaucoma, and others. If you detect that you experience problems with seeing at night, schedule an appointment with one of our eye doctors who will be able to shed some light on the issue.