Visual acuity is usually measured with a Snellen eye chart. The standard for “normal” vision is 20/20. This means that the person being tested sees the same line of letters on the chart at 20 feet that the person with normal vision sees at 20 feet.
A visual acuity of 20/70 means that the person being tested sees at 20 feet what a person with normal vision can see at 70 feet.

The vitreous is a clear, gel-like substance that fills the area between the lens and the retina. The pressure of the vitreous allows the eye to hold its shape. It also keeps structures like the retina in place.
With age, the composition of the vitreous changes. It may liquefy, allowing small bits of debris to float freely. Sometimes, miniscule collagen fibers clump together within the vitreous. Both create black, spidery flecks called floaters seen in the field of vision. Floaters are generally harmless but will remain within the vitreous unless surgically removed. The changing composition of the vitreous may also cause it to pull on the retina, sometimes resulting in a macular hole or a detached retina.