A sudden onset of floaters and flashing lights could be completely benign or a medical emergency. If those symptoms arise suddenly, it is imperative that you have a dilated fundus exam to rule out the potential of a detached retina or retinal tear.
The eye is a fluid filled structure. The fluid gives the eye its shape and would collapse like a balloon without air if not filled with the normal fluid volume. There is a transparent zip lock storage bag like structure called the vitreous, which contains the fluid volume, and is attached loosely to the retina. As a young person, the fluid contents of the eye is the consistency of grape jelly and kind of just giggles when you move. As you gain more life experience, usually around the age of 40, the fluid contents undergoes a process call "syneresis", which means it liquifies and becomes much more mobile. The increased motion inside the eye, combined with the more brittle nature of the vitreous as time goes by, can create the perfect storm, whereby the vitreous either creates a horseshoe tear in the retina, a partial or complete retinal detachment, of a completely benign but troublesome condition called a posterior vitreous detachment.
The first two are a medical emergency, and the latter is disturbing and annoying, but completely benign. The only way to properly evaluate and differentiate between the two is to have a dilated fundus exam.
The mechanism for the flashing light symptoms is related to the photosensitive nature of the RPE (Retinal Pigmented Epithelial) cells in the retina. There are no pain receptors in the retina. Therefore, those cells can only be stimulated by the presence of light, or by mechanical stimulation. If the vitreous inside the eye comes loose and begins to tug on the retina, that constitutes mechanical stimulation and the cells fire with your perception of a flashing light.
If the vitreous comes loose from the retina without tearing or detaching it, the transparent bag can then hang in the sight line and cast a shadow on the retina. The "floater" is your perception of the shadow that is cast on the retina. If you try to follow the image you perceive, the object moves and the image moves, resulting in you "chasing the shadow". In this instance, you can never look directly at the virtual image, as it always appears away from your line of sight. These symptoms can be quite disconcerting but are again completely harmless. Over time, the vitreous will completely separate and drop to the floor of the orbit. It becomes the snow in the snow globe for the rest of your life, and you may see occasional floaters when you shake up the globe with excessive eye movement.
There is a slightly increased incidence of retinal detachment associated with the onset of the floating symptoms, that lasts for one year. After the year passes, the incidence of retinal detachment drops to the same level of occurrence as everyone else your age.
As a general rule the following are signs and symptoms of a retinal detachment, which indicate the necessity for a prompt and urgent visit to your eye care professional for immediate evaluation:
- A curtain or a veil crosses in front of your sight line obscuring your vision repeatedly.
- You see a shower of flashing lights where there is no reasonable cause to see these lights.
- You see lightning bolts across the sky when there is no storm to explain it.
- You see a sparkler effect, similar to that of lighting that fiery metal stick around the Fourth of July, but there is no stick in your hand.
- You have the perception that you are walking through a swarm of gnats, but there are no gnats present.
- You see a pinkish or reddish tinge to the vision in one eye when compared to the other, while looking at a solid white background.