Eye Health Facts
Seeing in the dark
Vision in the dark continues to improve for about 30 minutes after being in bright light, as our eyes switch over from the colour-rich, crisp vision of daylight to the less crisp but more sensitive vision of night.
Once the eyes are adapted to dark, their most sensitive area is off to one side of 'straight ahead', making it possible to sense something out of the corner of your eye that disappears when you look straight at it.
Retinal degenerations, a genetic condition called retinitis pigmentosa, and Vitamin A deficiency can all reduce night vision.
Eye Health Facts
Ever wondered why cutting onions makes you cry?
As you slice an onion, the onion cells release a gas into the air. When this gas contacts the eye, it turns into weak sulphuric acid in the moist tear layer that coats the eye. Nerve endings in the cornea react to the acid, causing the sting, and trigger the lacrimal (tear) glands to produce lots of tears in an attempt to further dilute and flush away the acid.
If onions are in water, or near running water when cut, there will be much less gas in the air, and you are less likely to start crying.