The space between the crystalline lens and the retina is filled with a clear, gel-like substance called vitreous. In a newborn, the vitreous has an egg-white consistency and is firmly attached to the retina. With age, the vitreous thins and may separate from the back of the eye. This is called posterior vitreous detachment (PVD), a very common, usually harmless condition.
As the vitreous pulls free from the retina, it is often accompanied by light flashes or floaters. Floaters are caused by tiny bits of vitreous gel or cells that cast shadows on the retina. Flashes occur when the vitreous tugs on the sensitive retinal tissue.
There are other more serious causes of flashes and floaters, however. Retinal tears, retinal detachment, infection, inflammation, haemorrhage, or an injury such as a blow to the head may also cause floaters and flashes. (Have you ever seen stars after bumping your head?) Occasionally, flashes of light are caused by neurological problems such as a migraine headache. When related to a headache, the flashes of light are seen in both eyes and usually lasts 20-30 minutes before the headache starts.
Notify your eye care practitioner immediately if you notice a sudden shower of floaters, new light flashes, a veil or curtain obstructing your vision, or any other change. The eye care practitioner will dilate your pupils with drops and examine the vitreous and retina inside the eye with an ophthalmoscope.
Because of the risk, surgery is rarely indicated for PVD except when the floaters obscure the vision. In these cases, surgical removal of the vitreous (vitrectomy) may be considered only if the vision is significantly affected. This treatment is rarely needed since floaters typically become less bothersome over a period of weeks to months as they settle below the line of sight.
If the flashes and floaters are related to a problem other than a PVD, surgical treatment may be required.
It is important to periodically assess the vision of each eye. Many problems can be detected early by simply comparing both eyes.
To test your vision:
Report any new symptoms or changes in vision to your eye care practitioner.
Illustrations by Mark Erickson
With acknowledgement to St. Lukes Eye Hospital.