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Your Optometrists in the Santa Cruz area!

Your Optometrists in the Santa Cruz area!

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Night Vision



Everyone has found themselves in the dark, at one time or another. You need several moments to get used to the dark and then objects in the room begin to re-appear. This process, ''dark adaptation,'' causes our eyes to adjust to the dark.

Night vision requires a combination of biochemical, physical and neural mechanisms – for granted. How does it actually happen? Let's start by exploring the eye and its complex anatomy. The retina is a layer of cells at the back of the eye. The portion of the retina behind 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 have the capacity to function even in low light conditions. Those cells are absent from the fovea. What's the functional difference between these two cell types? Basically, details and colors we see are sensed by cone cells, while the rods are sensitive to light.

This information is significant because, when you want to see something in the dark, like a faint star in the night sky, instead of focusing right on it, try to use your peripheral vision. If, on the other hand, you focus on the object itself, you'll use the fovea, which is made up of cone cells that are less responsive in low light conditions.

Another part of the process is pupil dilation. The pupil grows to it its largest diameter within 60 seconds but it takes about half an hour for the eye to achieve full light sensitivity. During this time, your eyes become 10,000 times more sensitive to light.

Here's an example of dark adaptation: when you enter a darkened cinema from a bright lobby and have a hard time finding somewhere to sit. After a while, you get used to the dark and see better. This same thing occurs when you're looking at the stars in the sky. At the beginning, you can't see very many. If you keep looking, your eyes will dark adapt and the stars will gradually appear. It takes a few noticeable moments until you begin to adapt to regular indoor light. Then if you go back outside, that dark adaptation will be lost in a moment.

This explains why many people have difficulty driving at night. If you look at the ''brights'' of a car heading toward you, you may find yourself momentarily unable to see, until that car passes and your eyes once again adjust to the night light. To prevent this, don't look directly at the car's lights, and learn to use your peripheral vision in those situations.

If you're beginning to find it increasingly difficult to see at night or in the dark, book a consultation with our doctors who will see if your prescription needs updating, and rule out other and perhaps more severe reasons for worsening vision, like macular degeneration or cataracts.