Helen Keller, the disability rights advocate who lost her sight and hearing at 19 months of age, famously warned of “having sight but no vision”. Hers was a metaphor on living. But what happens to our eyesight as we age? And how common is it to have sight, but poor vision?
More specifically, how do we know when we need to make changes in our lives because we are not seeing as well as we used to? Driving, for example, is an intensive visual undertaking. But glare sensitivity and reductions in visual field are significant predictors of involvement in a crash. No amount of wisdom will help in the seconds before an accident you did not see coming.
Macular degeneration is a leading cause of driving accidents involving seniors. It’s also the main reason for being classified as legally blind for those over 55 years of age. The macula is a pin-sized area in the retina at the back of the eye that transmits images to the brain. Like a rifle bullet, it can zero in on small-sized distant objects. When the macula develops degenerative changes, nighttime driving becomes especially hazardous.
Other changes occur in the eye as we age. Like other parts of the body, the eyelids begin to droop providing less peripheral vision.
The pigmented iris that makes us brown or blue-eyed involve tiny muscles that fail to increase the size of the pupil to let more light strike the retina. This loss of vision is not detectable during the day. But driving a car with droopy eyelids and small pupils has the same effect as wearing sunglasses while driving at night.
Older drivers are also unable to adapt as quickly to changes in intensity of light. On occasion we’ve all complained, "Why didn’t that idiot turn off the high beams?" In this situation an aging iris contracts more slowly to the blazing light. But once the car has passed, it’s also slow in dilating to provide more light for the dark road ahead. A light pigment called rhodopsin, that helps adjust to night vision, also decreases as we age.
Today, most people are aware of the risk of developing cataracts in the lens in later years. The less transparent lens decreases the amount of light striking the retina and worsens night driving.
The final problem for the aging eye is photoreceptors in the retina. These cells transmit the image of an upcoming car to the brain. Older adults have lost one-third of these cells.
What can you do to decrease the hazards of driving at night? Mother urged us to eat our carrots to maintain good vision and she was partly right. Carrots are rich in vitamin A needed to regenerate rhodopsin.
There’s no sure way to stop macular degeneration. Some authorities advise people to take a daily supplement containing lutein, a macular pigment based on research showing this antioxidant helps to slow down this disease. Others say eating a diet rich in fruits and vegetables makes more sense.
Cataract surgery can improve night vision.
A sure way to survive night driving is to be realistic about your ability to see well in the dark. Good sense dictates that as visual acuity decreases, it’s prudent not to drive after sunset.
Helen Keller embodied the triumph of perseverance over tragedy. She had youth and a good teacher on her side. There is honour, too, in accepting when you have sight but poor vision, and don’t get behind the wheel.
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