By Grant Brown, ABOM
For most of our history, the fading of daylight into twilight and then to darkness gave our eyes time to slowly and naturally adapt to the lower light levels. We adjusted our lifestyles to the light level available. People’s habits were to get up with the rising sun and to retire when natural functional illumination ceased. The earlier artificial light, from animal fats and oils to kerosene lamps and lanterns, while extending our day, did not have the intensity to greatly affect our dark adaptation.
With the advent of electricity, the increased level of illumination contrast from well-lit areas to darkness is so much more abrupt. This greatly affects our ability to adapt at a pace necessary for not only our safety but also the safety of those around us. During the dark adaption process, contrast with our surroundings also changes which causes us to loose depth perception and acuity in not only our immediate but also our distant environment.
Our pace of life, especially with the speed of our transportation, has the potential to have a devastating effect on our lives. Most of us have experienced this while driving at night in areas that are not lit with artificial light. We go from maximum adaption, to quickly being overloaded from the intensity of car lights coming towards us, sometimes not dimmed, to instant darkness again when the car passes. Weather conditions, especially rain, snow or fog just exacerbate this already dangerous scenario. The National Highway Traffic and Safety Administration tests show that the delay in return to night adaption can and does lag behind the probable distance your car travels within that time.
Everyone has an adaption period in this scenario. However, many of us have an additional adaption time delay because of age, cataracts, medication, physical limitations as well as possible lack of adequate vision correction. Anyone with any kind of adaption delay experiences this effect with a greater severity. The NHTSA reports that these limitations can easily double, triple, quadruple or more our normal adaption time, and subsequently our reaction time.
The only reasonable answer right now is awareness of these situations and the appropriate adjustments for safety. Give yourself time to adapt. Adjust your travel schedules when possible. Drive slower and be more aware of your surroundings and limitations. Be aware of other drivers and always adjusts your lights properly if meeting a car, even if they don’t have the same courtesy for you. Do you really want BOTH of you to not see?
Grant Brown, ABOM, is a senior optician with the Prisma Health Eye Institute.