The vitreous is a clear gel that fills the area at the back of the eye. As we age, the vitreous undergoes a gradual process of becoming more liquid. Ultimately, the outer portion of residual gel separates from the retina. This change is normal and is called posterior vitreous detachment (PVD).
Small optical particles can move around within the vitreous fluid and become visible to the patient as floaters. In many eyes, there are areas of strong adhesion between the vitreous gel and the retina. PVD can cause pulling in these areas resulting in flashes of light. If the traction results in a retinal tear, vitreous fluid can seep under the retina and cause retinal detachment.
Retinal tear and retinal detachment are vision-threatening emergencies and require prompt treatment with laser and sometimes surgery. About 15% of eyes with flashes of light and floaters have a retinal tear, so it is important to schedule a retina examination if you experience a sudden onset of these symptoms.