What are eye flashes?
Flashes of light in the vision are exactly what they sound like: brief, sudden sparks or arcs of light that appear without any obvious external source. They tend to appear at the edges of your vision, last for only a fraction of a second, and are often most noticeable in dim or dark conditions.
The medical term is photopsia, and they are one of the more common symptoms that bring people to the eye clinic. In the majority of cases, they are caused by something physically tugging on the retina, the light-sensitive layer at the back of the eye. Understanding that cause makes the symptom far less alarming, though it also explains why certain accompanying features deserve prompt attention.
Why do flashes happen?
The inside of your eye is filled with a clear gel called the vitreous. In youth, this gel is firmly attached to the retina all the way around. As you get older, the gel gradually shrinks and liquefies, a process that is entirely normal. At some point, usually between the ages of 50 and 70, the gel may pull away from the retina in a process called a posterior vitreous detachment (PVD).
When the gel tugs on the retina during this process, the retina responds in the only way it knows: by generating a signal that the brain interprets as light. This is the flash you see. It is, in essence, a mechanical signal being misread as a visual one. The retina cannot tell the difference between genuine light striking it and the physical stimulus of being pulled, so it fires in the same way.
Flashes for this reason tend to be brief, arc-like, and peripheral. They often occur when you move your eyes quickly, particularly in dim environments where contrast is higher.
Mechanical stimulation of the retina by the vitreous produces flashes of light.
Retinal flashes versus migraine aura
Not all visual flashes are caused by the retina, and it is worth understanding the distinction. The two most common causes are posterior vitreous detachment on one hand, and migraine aura on the other. They look and behave quite differently.
Retinal flashes
These arise from traction on the retina. They are brief, usually lasting a fraction of a second. They tend to appear at the side of the vision, in one eye only. They are often described as a single flash or a brief arc of light, similar to what you might see if you press gently on a closed eye. They can recur over days or weeks while the vitreous is separating, and they are frequently associated with new floaters.
Migraine aura
A migraine aura is quite different in character. It typically begins as a small bright spot or zigzag shape in or near the centre of the vision, which then slowly expands outward over 20 to 30 minutes, forming a shimmering, crescent-shaped arc. It tends to affect both eyes simultaneously, not one side only, and it resolves fully, usually before or as a headache begins. It does not cause floaters.
If you are unsure which category your flashes fall into, an eye examination will clarify this. There is also a detailed comparison on the migraine aura versus retinal flashes page.
Migraine aura affects both eyes and expands over 20 to 30 minutes. Retinal flashes are brief, one-sided, and last a fraction of a second. If in doubt, have your retina examined.
Warning signs that need urgent assessment
Most flashes caused by a posterior vitreous detachment are harmless, but the vitreous pulling away from the retina can occasionally cause a small tear in the retinal tissue. A retinal tear is a serious finding because, if left untreated, it can allow fluid to track underneath the retina, potentially leading to a retinal detachment. This is a sight-threatening emergency.
The following symptoms alongside flashes should prompt you to seek same-day assessment from an eye doctor, or to attend an eye casualty department if your usual practice is closed:
- A sudden significant increase in the number of floaters
- A shower or swarm of new, dark floaters appearing at once
- A shadow, curtain, or veil at any edge of your vision
- Reduced central or peripheral vision
- Floaters that appear like a dark ring, cobweb, or curtain
- Flashes that are new, very frequent, or worsening rapidly
The reason these features matter is that they may indicate a retinal tear or the early stages of a retinal detachment. A retinal tear can usually be treated quickly and effectively with laser, but only if it is identified before the detachment has progressed.
What to do if you are getting flashes
If you have noticed new flashes of light in your vision, the first step is a dilated eye examination. This involves drops that temporarily widen the pupil so the ophthalmologist can examine the peripheral retina, where tears are most likely to occur. Without dilatation, peripheral retinal tears can be missed.
For most people, the examination will show a posterior vitreous detachment with no associated tear, and the flashes will gradually settle over the following weeks to months as the vitreous stabilises. Flashes that persist, but remain stable and without new accompanying features, do not usually require further intervention.
If a tear is found, it can typically be sealed with a brief in-office laser procedure, which is highly effective at preventing progression to a detachment. Early detection is the key, which is why prompt assessment matters even when you feel your vision is otherwise fine.
New flashes in one eye are worth having examined, even if you feel otherwise well. A dilated retinal examination takes only a few minutes and provides clear reassurance or early treatment if needed.
Understand your eye symptoms in more detail
Floaters and flashes explained →Common questions about eye flashes
Are flashes of light in your eye serious?
They are usually caused by a posterior vitreous detachment, which is common and rarely dangerous. However, new or sudden flashes alongside new floaters, a shadow in the vision, or any reduction in sight should be assessed the same day. These features can indicate a retinal tear.
What do retinal flashes look like?
They are typically brief, peripheral, arc-like flickers, often described as resembling a camera flash at the edge of the vision. They tend to occur in one eye and are most noticeable in dim lighting or when the eyes move quickly.
Do eye flashes go away on their own?
Flashes from a posterior vitreous detachment often settle over several weeks to months as the vitreous stabilises. New, worsening, or alarming flashes should always be assessed promptly.
What is the difference between eye flashes and migraine aura?
Migraine aura produces a shimmering, expanding zigzag arc across both eyes over 20 to 30 minutes. Retinal flashes are brief, in one eye only, and last a fraction of a second. They do not expand or resolve in the same way.
When should I go to A&E for eye flashes?
Seek urgent help if you notice new flashes alongside a sudden shower of floaters, a shadow or curtain in your vision, or any reduction in your visual field. These are the warning signs of a retinal tear or detachment, which need same-day assessment.
This page is for general educational purposes and does not constitute medical advice. If you are concerned about your symptoms, please seek assessment from a qualified eye care professional.
