Sunlight , under normal conditions,is not an enemy of the eyes.On the contrary,it is an essential element for healthy strong eyes. when eyes are deprived of sunlight for long periods of time,they become weak and oversensitive to light.It is well known that persons deprived of light for long periods of time lose their eyesight .An example of this is the slave miners who were totally deprived of sunlight for years and eventually lost the power of sight .