If we see an object by our two eyes we can only see a single object. Though each eye forms individual images on their own retinas but the brain combines the two images to make a single one. We can measure the distance accurately for having two eyes. So, it is very difficult to thread a needle keeping one eye closed.

Apart from that, due to the relative position of our eyes with respect to the object we see the right portion of the object better with our right eye and the left portion better with our left eye. If we see an object by our two eyes the superimposition of two images will happen and we will be able to see the object clearly.

The saline watery fluid that fills up the space between the eye lens and cornea is called aqueous humour. On the other hand, the jelly like substance that fills the gap between retina and eye lens is called vitreous humour.