Oh, to be 20 again

Some years ago, my wife and I were out at a local restaurant for dinner. Due to low lighting in the dining area, I couldn’t for the life of me read anything on the menu. We laughed because I had to go back into the well-lit lobby where I could actually read the thing.

This is just one of many indignities I’ve had to suffer as a result of advancing age, having to do with the pupils of my eyes. This is not a structure, but, rather, an aperture, much like that of a camera, that increases or decreases in size depending on the amount of light present. One of the routine neural tests is to shine a bright light into each eye to test whether the parasympathetic nervous input is functional; if so, the pupil constrictor muscle (iris) will contract, reducing pupil size and the amount of light entering the eyes.

On the flip side, a functional sympathetic system stimulates relaxation of the pupil dilator muscle, causing pupil size to increase under low light condi-tions. This lets more light into the eyes and aids a person’s vision. The sympa-thetic system controls the flight-or-flight response that helps a person cope with stressful situations, and increasing visual acuity is an important feature of this response.

The muscles that work to regulate pupil size weaken with age, reacting more sluggishly to light and dilating less effectively in the dark, and this increas-es the danger of driving at night. After the sun goes down, our depth percep-tion, color and contrast recognition, and peripheral vision become compro-mised. Only 25% of all driving occurs at night, but 50% of all accidents occur then. I recently received some tips from AAA for safer driving at night that are valuable things to consider:

1. Your field of vision is limited to the area illuminated by your headlights. Increase the typical distance between you and the car you’re following.

2. Don’t look directly into oncoming car lights, especially if the high beams aren’t turned down. It takes several seconds to readjust to the darkness after they pass.

3. If you have to drive extensively on a sunny day and then continue into night, wear sunglasses and then take them off after the sun goes down. If you’re wearing prescription glasses, try to use anti-reflective lenses.

4. Headlights can sometimes be uneven or pointed too low, even in new cars. If so, make sure they are adjusted to maximize your field of vision.

5. Those at age 60 need three times as much light as those at age 20 be-cause of pupil aging. Aging drivers should compensate by scanning further down the road and moving their heads as well as their eyes to overcome re-duced peripheral vision (see pic).

Finally, if this isn’t enough, annual eye exams become increasingly im-portant as we age, because problems such as glaucoma, cataracts or disease complications (eg, diabetic retinal deterioration) only add to the visual challeng-es of nighttime driving.