Night Blindness Quentin asked
Seems dumb but how would one know it wasn't just a dark night.
Isn't it something to do with how quickly one recovers from the glare of an oncoming headlights or is that something else.
Marty responded
If you are driving on a dark road at night and another car comes toward you with regular headlights (not highbeam headlights), the light blinds you for a few seconds and you can not see the road ahead after the other car passes (that's night blindness).
Night vision uses the rods and there are many more of these than the cones (color vision). To see well at night, low light activates many of the rods (vitamin A visual pigment). If retinol delivery to the eye is lower than it should be (stores in the liver go below 50,000IU) the eye is the first tissue in the body to be affected. You should not use all available rods when the light from a passing car hits the retina. Your unfired rods should allow you to see the road after the car passes. If active rod number is lower than normal (low retinol delivery to the eyes), you fire too many rods and have none in reserve to see after the light passes. You can not see well again until the fired rods come back online.
Cataracts will prevent good night vision but there the problem is getting enough light to the retina. Zinc and molybdenum deficiencies will also cause night blindness.
Liver requires zinc for retinol release and the cells that take up retinol require the retinol receptor which needs molybdenum to work.
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