Every time I think of driving at night, I hear the song “Blinded by the Light” in my head. In truth, either too much light or too little is challenging when driving at night. Too much light from the shock of intense glare inducing bright blue LED headlight lamps is blinding. Moreover, too little light is bad because we need light to see, and twilight and nighttime illumination levels reduce illumination levels making it hard to see. Aging eyes experience age-induced eye changes that reduce light transmission to the retina while increasing scatter, blur and glare. With age, the pupil loses its ability to dilate to the same degree as a young eye. Therefore, less light reaches the retina of an aged eye. At night we need every bit of light available for best night vision. With age, we have reduced numbers of rod photoreceptors in the peripheral macula. The macula is the central part of the retina used for the sharpest vision. We use rods in low light and dark conditions because they are very sensitive to a single photon of light, meaning they can detect light in low light and dark conditions. The aging eye experiences more glare and is slower to recover from glare. There is little in our nighttime environment that produces more glare than blue LED headlights at night when driving. Another factor that affects night vision and glare recovery is clogged Bruch’s membrane. Why? Because Bruch’s membrane delivers the blood flow that contains essential vitamin-A derivative, 11-cis-retinal, to the rod photoreceptors.
Without 11-cis-retinal, the rod cells rhodopsin regeneration does not occur after exposure to bright light, both slowing dark adaptation and glare recovery time. The very same gunk that clogs our arteries (cholesterol and waste products) and threatens heart health may also interfere with vitamin-A derivatives reaching the rod photoreceptor cells, according to Dr. Gregory Jackson, a researcher at the University of Alabama. Anything that interferes with rod photoreceptor regeneration at night is bad for night driving. More recently, I learned that night myopia affects a third of us. Even if we see well in the distance in the daytime, we can still experience night myopia. Most of us will develop cataracts at some point later in life, and the opaque crystalline lens caused by a cataract contributes to light scatter, increased glare and blur when driving at night. We have enough challenges with nighttime driving and aging eyes but night myopia does not have to be one of them. Read the IOT sponsored article on night myopia in this issue to learn about a unique challenge for night driving that 1 in 3 of us experience even if we are emmetropes.
• Deborah Kotob
Pro to Pro Director