Flashes are caused by the vitreous pulling or tugging at the retina. This is related to the aging process and is called a vitreous separation. Sometimes they can indicate a retinal detachment. Flashes could appear like a crescent-shaped streak, a lighting flash, or a camera flash. Floaters are caused by small particles of dead cells or other debris that become suspended in the vitreous clumping together and casting a shadow on the retina.
Most people have floaters in some degree and they are also related to the aging process.
They cast shadows on the retina and appear as spots or cobwebs. You should contact your ophthalmologist if you notice a new onset of flashes or floaters. Generally the eyes may continue to change until a person reaches their early 20 s. The changing of eye correction will often slow down during the teenage years. Refraction is the part of the exam that measures any visual change and a measurement of glasses prescription.