Sudden Floaters and Flashes: When Do You Need an Urgent Eye Ultrasound?
Suddenly seeing floaters or flashing lights in your vision can be frightening. Floaters may look like small dots, cobwebs, threads, shadows, flies, circles or moving specks. Flashes may appear as brief sparks, lightning streaks, camera flashes or flickering lights, often at the edge of vision.
In many cases, floaters and flashes are caused by age-related changes in the gel inside the eye. However, they can also be warning signs of a retinal tear or retinal detachment, which can permanently affect vision if not treated quickly.
Urgent Warning
Seek urgent medical, optometry or ophthalmology assessment if you develop a sudden shower of new floaters, new flashing lights, sudden blurred vision, a dark curtain or shadow in your vision, or sudden loss of part of your visual field.
These symptoms should not be ignored. Retinal tears and retinal detachment may be painless, but they can threaten vision if not treated quickly.
Quick Answer: Are Sudden Floaters and Flashes Serious?
Sudden floaters and flashes are often caused by posterior vitreous detachment, a common age-related change in the vitreous gel inside the eye. However, they can also be warning signs of a retinal tear, vitreous haemorrhage or retinal detachment.
Eye ultrasound, also called ocular B-scan ultrasound, may help when the back of the eye cannot be clearly seen, for example because of bleeding, dense cataract, corneal opacity or poor retinal view.
What Are Floaters?
Floaters are small shapes that appear to move across your vision. They often move when you move your eyes and may seem more obvious when looking at a bright background, such as a white wall, computer screen or blue sky.
Floaters may look like:
- Dots
- Lines
- Threads
- Cobwebs
- Small flies
- Rings
- Shadows
- Moving specks
Floaters are usually caused by changes in the vitreous, the clear gel-like substance inside the eye.
What Are Flashes?
Flashes are brief bursts of light seen in the vision. They can happen when the vitreous gel pulls on the retina. The retina is light-sensitive tissue at the back of the eye and converts light into signals that travel to the brain.
Flashes may appear as:
- Lightning streaks
- Sparkles
- Camera flashes
- Flickering arcs
- Light at the side of vision
- Brief bursts of light
When the retina is mechanically stimulated by traction, the brain may interpret this as light, even when no light is entering the eye.
Why Do Floaters and Flashes Happen?
Posterior Vitreous Detachment
The most common cause of sudden floaters and flashes is posterior vitreous detachment, also called PVD. As we age, the vitreous gel naturally becomes more liquid and begins to shrink. Eventually, it may separate from the retina.
PVD is common, especially after the age of 50. It is often harmless, but it can sometimes pull strongly enough on the retina to cause a tear. This is why new floaters or flashes should be assessed promptly.
Why Can a Retinal Tear Be Serious?
A retinal tear occurs when the retina develops a break. If fluid passes through the tear and collects behind the retina, the retina may lift away from the back wall of the eye. This is called retinal detachment.
Retinal detachment is serious because the retina needs direct contact with its underlying blood supply to function properly. If it becomes detached and is not treated quickly, permanent vision loss can occur.
Retinal Detachment Warning Signs
Seek urgent medical or ophthalmology assessment if you experience:
- A sudden shower of new floaters
- New flashes of light
- A dark curtain or shadow in your vision
- Sudden blurred vision
- Sudden loss of part of your visual field
- Floaters and flashes after eye trauma
- Symptoms in one eye that are new or worsening
- Any sudden vision change
These symptoms should not be ignored, even if there is no pain.
What Is the Pathophysiology Behind Retinal Detachment?
The retina is a thin, delicate layer of nerve tissue at the back of the eye. Its job is to detect light and send visual signals to the brain.
- The vitreous gel pulls on the retina.
- A small break forms in the retina.
- Fluid enters through the break.
- The retina begins to separate from the underlying tissue.
- The separated retina loses normal support and nutrition.
- Vision becomes distorted, blurred, shadowed or lost.
If the macula, the central part of the retina responsible for sharp vision, becomes detached, central vision may be severely affected. Early diagnosis is therefore essential.
What Is Vitreous Haemorrhage?
Vitreous haemorrhage means bleeding into the vitreous gel. If blood blocks the view of the retina, eye ultrasound may be particularly useful.
Vitreous haemorrhage may occur due to:
- Retinal tear
- Diabetic eye disease
- Retinal vein occlusion
- Trauma
- Abnormal fragile blood vessels
Symptoms may include:
- Sudden floaters
- Hazy vision
- Red or dark spots
- Sudden visual clouding
- Reduced vision
How Can Eye Ultrasound Help?
An eye ultrasound scan, also called an ocular B-scan, uses high-frequency sound waves to image the inside and back of the eye.
It can help assess:
- Retinal detachment
- Vitreous haemorrhage
- Posterior vitreous detachment
- Intraocular masses
- Lens displacement
- Some trauma-related changes
- Optic disc drusen in selected cases
- Internal eye abnormalities
Eye ultrasound is particularly helpful when the retina cannot be seen clearly through normal examination, for example due to bleeding, dense cataract, corneal opacity or poor view.
What Does a Retinal Detachment Look Like on Ultrasound?
On B-scan ultrasound, a retinal detachment may appear as a bright membrane lifted away from the back of the eye.
The ultrasound specialist may assess:
- Whether the retina appears attached or detached
- Whether there is vitreous haemorrhage
- Whether membranes are mobile
- Whether the macula may be involved
- Whether further urgent ophthalmology referral is needed
Ultrasound does not replace specialist ophthalmology assessment, but it can provide valuable information when the retina cannot be directly visualised.
Can Ultrasound Rule Out Every Retinal Tear?
No. This is very important.
Small retinal tears may not always be visible on ultrasound, especially if the view is limited or the tear is subtle. If you have new flashes or floaters, you should still have urgent eye assessment, usually including dilated retinal examination by an optometrist, ophthalmologist or emergency eye service.
A normal ultrasound can be reassuring, but it does not replace full retinal assessment when symptoms are concerning.
Who Is More Likely to Develop Retinal Tears or Detachment?
Risk factors include:
- Increasing age
- Short-sightedness
- Previous retinal tear
- Previous retinal detachment in the other eye
- Eye trauma
- Previous cataract surgery
- Family history of retinal detachment
- Diabetic eye disease
- Inflammatory eye disease
People with these risk factors should be especially cautious with new visual symptoms.
When Should You Book an Eye Ultrasound?
An eye ultrasound may be useful if:
- You have floaters or flashes and the back of the eye cannot be clearly seen
- Vitreous haemorrhage is suspected
- Retinal detachment is suspected
- Dense cataract prevents retinal examination
- There has been eye trauma and the globe is intact
- There is concern about an intraocular abnormality
However, urgent symptoms should be assessed promptly and not delayed while waiting for a routine scan.
What Should You Do If You Have Sudden Floaters or Flashes?
- Do not ignore new symptoms.
- Avoid driving if vision is affected.
- Seek urgent optometry, ophthalmology, NHS 111, eye casualty or emergency assessment.
- Mention whether symptoms started suddenly.
- Report any dark curtain, shadow or loss of vision.
- Ask whether eye ultrasound is needed if the retina cannot be clearly seen.
Private Eye Ultrasound in London
London Private Ultrasound provides private ocular B-scan ultrasound for selected eye conditions where internal eye imaging is clinically appropriate.
- Book a private eye ultrasound scan in London
- View London Private Ultrasound price list
- Contact London Private Ultrasound
Important: If you have sudden vision loss, severe eye pain, a dark curtain or shadow, or symptoms after trauma, seek urgent ophthalmology or emergency assessment immediately. Do not delay urgent care while waiting for a routine appointment.
Frequently Asked Questions
Are sudden floaters and flashes always serious?
Not always. They are often caused by posterior vitreous detachment, which is common with age. However, they can also be warning signs of retinal tear or retinal detachment, so sudden new symptoms should be assessed urgently.
What is posterior vitreous detachment?
Posterior vitreous detachment occurs when the vitreous gel inside the eye shrinks and separates from the retina. It is often harmless but can sometimes pull on the retina and cause a tear.
Can eye ultrasound detect retinal detachment?
Eye ultrasound can help detect retinal detachment, especially when the back of the eye cannot be clearly seen due to bleeding, dense cataract or poor view. Final management should still be guided by ophthalmology assessment.
Can a normal ultrasound rule out a retinal tear?
No. Small retinal tears may not always be visible on ultrasound. If you have new floaters or flashes, you still need urgent retinal assessment.
Should I book an ultrasound first or seek urgent eye assessment?
If you have sudden floaters, flashes, blurred vision or a dark curtain or shadow, seek urgent eye assessment first. Eye ultrasound may be arranged if clinically needed.
Final Thoughts
Sudden floaters and flashes are often caused by posterior vitreous detachment, a common age-related change in the gel inside the eye. However, they may also signal a retinal tear or retinal detachment, which can threaten vision if not treated urgently.
Eye ultrasound can be extremely useful when the retina cannot be clearly seen, especially in cases of vitreous haemorrhage, dense cataract or poor view. It can help detect retinal detachment and guide urgent referral decisions.
If you develop sudden floaters, flashes, blurred vision, or a dark curtain or shadow in your vision, seek urgent medical or ophthalmology assessment immediately.
Book a Private Eye Ultrasound Scan in London
London Private Ultrasound provides private ocular B-scan ultrasound for selected eye conditions where internal eye imaging is clinically appropriate.
References
Article Preparation and Clinical Review
This patient information page was prepared with AI-assisted editorial support and reviewed for clinical accuracy by:
Dr Pedram Aghaei — Vascular Scientist, SVT reg. SVT 679 · Registered Clinical Technologist, RCT reg. 93290 · BMUS 20702
Dr Hosna Rashidi — BMUS 29386 · SVT reg. M11114