Seeing black dots is natural phenomenon in most cases which is due to vitreous liquefaction.. it means with increasing age fluid inside in the eye ,between lens and retina , which is in jelly state becomes more liquid and it casts a reflection over the retina which u see as black dot or also known as floaters.. more u try to focus on it, u will see it for longer duration..

Most floaters not a problem. But sometimes  they can be signs of a serious condition. Consult  an ophthalmologist if Thereare lot of new floaters If it is associated with flashes If a curtain covers part of your vision

These are called floaters. And are usually nonpathological.please learn to omit them but get your fundus examination done so as to rule out any retinal problem.