Drive during the day and you can pretty much cruise on autopilot. But when it gets dark out, you might find it harder to navigate the road.

Darkness presents a challenge for almost every driver, says Rebecca Taylor, M.D., a clinical spokesperson for the American Academy of Ophthalmology. That’s because poor lighting can cause blurred and cloudy vision.

Blame the inner workings of your eye. During a bright day, your pupils—which control how much light enters your eyes—stay small.

This allows light to zoom into your peepers like a laser beam. It takes almost a straight, uninterrupted path to your eye’s retina, giving you a clearer, more focused image for your brain to process.

Once that picture lands on your retina, photoreceptors in your eyes called cones perk up and pick up the sharpest image and the most vivid colors, helping you see greater detail.

But when it’s dark out, your pupils grow larger, Dr. Taylor says.

Since bigger pupils suck in extra beams of light, the light doesn’t enter your eyes as straight as it does on a bright day. As a result, you can’t focus or see as well.

And to make matters worse, your cones don’t kick in when it’s dark; different photoreceptors called rods come into play instead. Rods don’t see as sharply and don’t pick up on color at all.

This hurts the clarity of your vision, as well as your ability to distinguish hues.

A little degradation is normal, Dr. Taylor says, but if you have significant trouble seeing at night, you should make an appointment with your eye doctor.

“Poor vision during twilight is usually one of the earliest manifestations of someone who is becoming a little nearsighted,” she says.

So you might need glasses or contacts, or a new prescription.

Dry eye can make your night vision even worse, since the condition dries out your cornea and blocks light rays from landing properly on your retina.
You could also have cataracts, which are cloudy or opaque regions on the lenses of your eyes. Cataracts can make you see a glare and halos around lights at night.

If you suffer a huge drop from day to night vision, it may signal a systemic condition like diabetes, or a genetic disorder called retinitis pigmentosa—which could lead to blindness.

But don’t stress: Retinitis pigmentosa is extremely rare in young, healthy guys without a family history of the disease.

So what can you do about your night driving issues? Unfortunately, you can’t change the way your pupils respond to the dark. So you’ll probably always experience a bit of a decline, says Dr. Taylor.

But a pair of special specs may help, she says.

Wearing glasses with a yellow tint or an anti-reflective coating could cut down on glare and enhance your vision when you’re driving in low-light conditions. Ask your eye doctor for details.

CHRISTA SGOBBA