Adjusting to the dark

If you’re over 50, your night-time vision probably isn’t what it used to be. Here’s how to stay safe.

The typical 50-year-old needs twice as much light to see as well after dark as a 30-year-old, according the US National Safety Council. Yet few of us make the necessary lifestyle adjustments to stay safe both on the road and at home.

It’s like wearing sunglasses at night
Eyes adapt to dim light or darkness by widening the pupils to let in as much light as possible. The iris, or the coloured part of the eye surrounding the pupil, contains tiny muscles that control the size of the pupil. And as we age, these muscles weaken and do not respond as well to the need to let in more light.

This results in a pupil too small for seeing well in dim light – sort of like you’ve put on sunglasses at night.

The less responsive muscles in the iris also affect the eye’s ability to adjust to sudden light changes, such as when a car with its headlights on approaches and then passes. A driver may also experience a decrease in depth perception.

Other age related changes include the formation of cataracts, which makes the lens less transparent and reduces the amount of light reaching the retina. Cataracts can cause light to scatter, resulting in the temporarily blinding glare from the headlights of an approaching vehicle.

To improve night vision, experts advise protecting your eyes during the day by wearing sunglasses and a hat with a brim when the weather is sunny. Bright sunlight can bleach the photoreceptors and thereby, lengthen the time it takes for your eyes to adjust to the dark. Normally it takes 30 to 60 minutes for full adaptation to the dark, but being in bright sunlight for two or three hours can delay this adaptation by hours.

Road safety
Traffic deaths are three times more frequent at night than during the day, even though only 20 per cent of driving is done after dark. While fatigue and alcohol can contribute to this risk, experts say the biggest factor is darkness. A full 90 per cent of a driver’s reaction depends on vision.

The experts offer these tips for driving at night.

• Make sure your vehicle is in good working condition, especially your lights and brakes.

• Clean the windshield thoroughly, inside and out at least weekly. Make sure the windshield washer reservoir is full and operational. Windshield wipers should also be clean and free of defects.

• Slow down and increase the distance between you and the vehicle ahead of you. You should be able to stop inside the area illuminated by your headlights. If you overdrive your headlights, you create a blind crash area in front of your vehicle.

• Clean the headlights. Even a thin layer of grime can reduce the light they cast by about 90 per cent, which in turn reduces how well you can see.

• Use high beams wherever possible without creating a traffic hazard for oncoming traffic. Driving with high beams can double your visibility. Glare recovery is a major concern when driving at night. The average person needs 10 seconds to recover from glare, but the recovery time increases with age. To deal with glare:

  • Look beyond the oncoming headlight beam and not directly into it.
  • Reduce the illumination of the dashboard lights. This will eliminate glare into the eyes or onto the windshield.
  • After experiencing glare from an oncoming vehicle, gradually let off the gas, look to the right slightly, and resume normal driving after the vehicle passes.

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