Everyone has found themselves in the dark, at one point or another, whether it be during childhood, due to a power outage, or just waking up in the middle of the night. You need several moments to get used to the dark and then you are able to see better. This process, ”dark adaptation,” allows us to see even when there’s almost no light.
In order for night vision and dark adaptation to happen, many physiological, neurological and biochemical mechanisms have to take place behind the scenes. How do our eyes actually function in low light? Firstly, let’s examine the eye and its anatomy. Every eye uses rod cells and cone cells, at the back of the eye; or, to be precise, on the retina. Together they make up the sensory layer that helps the eye see colors and light. The rod and cone cells exist throughout the entire retina, with the exception of the small area opposite the pupil known as the fovea. This has only cone cells, and its primary function involves focusing. What’s the difference between rods and cones? Basically, cones contribute to color vision, and rod cells let us see black and white, and are light sensitive.
Let’s put this all together. Imagine struggling to focus on something in the dark, like a distant star in the night sky, instead of focusing right on it, try to use your peripheral vision. 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 dilate in low light. Your pupil grows to it its maximum size within 60 seconds but it takes approximately 30 minutes for the eyes to achieve full light sensitivity and, as everyone has experienced, during this time, your ability to see in the dark will increase greatly.
Here’s an example of dark adaptation: when you go from a very light-filled area to a dim one for example, when coming inside after spending time in the sun. Despite the fact that your eyes require a few noticeable moments to get used to the dark, you’ll quickly be able to re-adapt upon your return to bright light, but then the dark adaptation process will have to begin from scratch if you go back into the dark.
This is actually why a lot people have difficulty driving their cars at night. If you look right at the headlights of an oncoming car in traffic, you are momentarily unable to see, until that car passes and your eyes once again adjust to the night light. A helpful way to avoid this is to avoid looking right at headlights, and learn to use peripheral vision to observe oncoming traffic at night.
There are a number of conditions that may cause difficulty seeing in the dark, including: a nutritional deficiency, cataracts, glaucoma, or some other visual interference. Should you begin to detect that you experience trouble in the dark, schedule an appointment with one of our eye care professionals who will be able to identify and rectify it.