Flashes of light and floaters are among the most common complaints in ophthalmology, and in the great majority of cases they are entirely benign. But they are also precisely the warning signs of retinal detachment — an emergency that can cause permanent vision loss. The key is not to panic at every floater, but to know how to tell the routine phenomenon from the change that requires urgent attention. That is what this page explains.
What posterior vitreous detachment is
The cavity of the eye is filled with a clear gel called the vitreous, which is attached to the retina. With age the gel liquefies and shrinks, and at some point separates from the retina — a process called posterior vitreous detachment (PVD). This is a common and natural process that most people go through after age 60, and it is not in itself dangerous. But it is the common cause of the two familiar symptoms: floaters — fibres in the gel that cast shadows on the retina — and flashes of light, produced when the vitreous tugs gently on the retina during the separation.
When it is benign
A few floaters that have been with you for a long time, that do not change, almost always stem from a benign ageing of the vitreous. They may be a nuisance when reading or against a bright background, but they do not threaten vision, and the brain learns to ignore them over time. An “ordinary” posterior vitreous detachment is also benign — but because in a small proportion of cases it tears the retina, it is advisable to be examined within a short time of its onset, even when it seems innocent.
When it is an emergency — the warning signs
Four changes are not routine, and require an urgent dilated eye exam, usually the same day:
- A sudden shower of new floaters — far more than usual, appearing all at once.
- Recurrent flashes of light, especially new or increasing.
- A shadow, curtain or dark screen moving across part of the visual field.
- A sudden loss of part of the vision.
These signs may indicate that the vitreous detachment has torn the retina, or that the retina is already beginning to detach. There is no way to tell from the outside — only an examination of the peripheral retina with dilated pupils can determine it. The simple rule: a sudden change in floaters or flashes is not something to “wait and see”.
From a tear to a detachment
When the vitreous pulls and tears a hole in the retina, fluid from the vitreous cavity can seep through the tear and lift the retina from its place — this is a retinal detachment. The detached retina loses its blood supply and function, and if the process is not stopped, it spreads.
Here timing is especially decisive: as long as the centre of vision (the macula) is still attached, prompt surgery gives the best chance of preserving central vision. Once the detachment reaches the centre, sharp vision is harmed — and sometimes does not fully return even after successful surgery. So the difference between coming in the same day and coming a week later can be the difference between vision preserved and vision lost.
Diagnosis and treatment
Diagnosis is made with a dilated fundus exam, which lets the physician examine the peripheral retina and detect tears. When the vitreous is clouded (for example by bleeding) and the retina cannot be seen, an ultrasound examination is used.
A retinal tear that has not yet progressed to a detachment is treated in the clinic: laser (retinopexy) or freezing (cryopexy) create a “weld” around the tear and prevent it from widening. This is effective preventive treatment, and it is exactly why it is worth catching a tear early.
A retinal detachment is treated surgically, according to the type and location of the detachment: vitrectomy (removing the vitreous and repairing from within), an external buckle (scleral buckle), or the injection of a gas bubble (pneumatic retinopexy). What they have in common: earlier is better.
Who should be especially alert
The risk of retinal detachment is higher in high myopia, after cataract surgery, after eye trauma, with a family history, and in anyone who has already had a detachment in one eye. Advanced diabetic retinopathy also sometimes causes a tractional detachment. People in these groups should know the warning signs in advance, in order to act immediately if they appear.
Bottom line
Flashes and floaters are usually a benign part of the eye’s ageing, and there is no need to panic at every one of them. But a sudden change — a shower of floaters, increasing flashes, or a curtain over the field of vision — is the way retinal detachment announces itself, and it is never a “wait and see”. An urgent dilated exam is the only way to tell a benign vitreous detachment from a tear, and sealing a tear in time prevents a detachment. For background on other retinal diseases see macular degeneration and eye diseases; on how a visual impairment translates into disability percentages, see eye disability assessment.
The information on this page is general and not a substitute for a personal examination and medical advice. Anyone noticing new flashes, a shower of floaters or a shadow in the visual field should seek an ophthalmologist or an eye emergency room urgently.
Frequently asked questions
I have floaters in my vision. Is that dangerous?
In most cases, no. Floaters usually arise from ageing of the vitreous — the clear gel that fills the eye — and from posterior vitreous detachment, a common and natural process after age 60. They are annoying but benign, and the brain adapts to them. But a sudden change — a shower of new floaters, flashes of light, or a shadow moving across the field of vision — is not routine, and requires an urgent dilated eye exam to rule out a retinal tear.
What are the warning signs of retinal detachment?
Four signs require an urgent exam: the sudden appearance of many new floaters; recurrent flashes of light, especially new or increasing; a shadow, curtain or dark screen moving across part of the visual field; and a sudden loss of part of the vision. These signs may indicate that the vitreous has torn the retina, or that the retina is beginning to detach. The earlier the examination, the greater the chance of preserving vision.
How are a retinal tear and a detachment treated?
A retinal tear that has not yet progressed to a detachment is sealed in the clinic with laser (retinopexy) or freezing (cryopexy), which surround the tear and prevent it from spreading. An actual retinal detachment is a surgical emergency, treated by surgery — vitrectomy, an external buckle (scleral buckle) or the injection of a gas bubble. The sooner the surgery is done, and especially while the centre of vision is still attached, the better the outcome.
Who is at higher risk of retinal detachment?
The risk rises with high myopia (nearsightedness), after cataract surgery, after eye trauma, with a family history, and in anyone who has already had a detachment in the other eye. Advanced diabetic retinopathy can also cause a tractional detachment. People in these groups should know the warning signs and not delay if they appear — time is a decisive factor.
