Authored by Nicholas Oliver Corey Kuzik
Reviewed by Stephen Carrell, PGY-4 at University of Alberta
Edited and posted by Yosra Er-reguyeg
Aug 28, 2026 | 5 min
Part 5: Flashes & Floaters on Your Ophthalmology Elective
Recently, I was shadowing the ophthalmology weekend call emergency clinic where the chart note said patient complains of a floater. Aside from the resident’s frustration at being woken up at 2 am for a floater, we became much more interested when the patient described it as a spot of blurred or missing vision that has been there for a few days. Flashes and floaters should prime you to expect a posterior vitreous detachment, but you need to first rule out a retinal tear or detachment. A persistent blurry or missing area/spot might be a scotoma, which should make you think about pathology involving the retina or optic nerve, including ischemia if the onset was sudden. If instead the patient describes shimmering zig-zags that slowly spread across both sides of their vision for 20 minutes before disappearing. Now we are thinking about migraine aura.
Sometimes you get the same vague description of “something is weird with my vision”, but that can take you to very different differentials.
The tricky part is taking subjective descriptions from your patient, looking for objective findings to support or challenge your differential, and ultimately understand what your patient is actually seeing.
For flashes, floaters, and other visual disturbances, you can start with four questions:
Those four questions will take you surprisingly far.
First: What Are They Actually Seeing?
Floaters
Floaters are mobile opacities that patients may describe as: dots, specks, cobwebs, threads, bugs, squiggly lines, etc. They tend to move with the eye and may drift slightly after eye movement stops. So have the patient move their eye left and right and ask if the floater is drifting.
A few longstanding floaters are common.
A sudden shower of new floaters is different. That should make you think about posterior vitreous detachment, retinal tear, vitreous haemorrhage, or retinal detachment.
Flashes
Flashes, or photopsias, may occur when the retina is mechanically stimulated. Patients may describe:
New unilateral flashes, particularly when paired with new floaters, should make you think about vitreoretinal traction and a possible retinal tear.
But flashing lights can also come from the brain. That is where the history becomes useful.
Positive vs Negative Visual Phenomena
This distinction is simple and helpful.
Positive phenomena
The patient sees something that is not normally there:
Negative phenomena
Something that should be visible is missing:
New negative symptoms should immediately raise your concern. A curtain or progressive shadow is particularly worrying for retinal detachment.
One Eye or Both?
Monocular
Think more about:
Posterior vitreous detachment, retinal tears, and retinal detachment usually produce monocular symptoms.
Binocular
Think more about:
The catch is that patients are often not sure whether something happened in one eye or both. If the symptom is happening in front of you, have them cover each eye separately.
The Classic Retinal Pattern
The pattern that should immediately get your attention is:
New unilateral flashes + new floaters ± curtain or field loss
Think about:
Posterior Vitreous Detachment
Posterior vitreous detachment itself is common and often uncomplicated. As we age the gel-like vitreous humour liquefies, causing it to shrink and pull away from the retina. This is a posterior vitreous detachment.
Patients may notice:
The problem is that vitreous traction can create a retinal tear during that process. So, it is essential that you conduct a thorough exam to ensure there are no retinal tears or detachments.
Retinal Tear and Retinal Detachment
Features that should increase your concern include:
Important risk factors include:
One important pearl:
Normal central visual acuity does not rule out a retinal tear or peripheral retinal detachment.
The macula can still be attached while the peripheral retina is detaching.
That is exactly why the history and peripheral exam matter.
A Shower of Floaters Can Be Blood
Vitreous haemorrhage may present as:
Possible causes include:
If the view to the fundus is poor because the vitreous is full of blood, that is not reassuring.
A poor view is a finding.
Retinal Flashes or Migraine Aura?
This is one of the most useful distinctions to start learning.
More suggestive of retinal photopsias
More suggestive of migraine aura
A simple way to remember it:
Migraine tends to build and travel. Retinal traction tends to flash.
Not perfect, but useful.
Other Visual Disturbances Worth Recognizing
Patients will often describe things that are not really flashes or floaters.
Sudden monocular missing vision
A sudden dark, grey, or missing area in one eye is different from a floater. If the deficit persists, think about pathology affecting the retina or optic nerve, including retinal vascular occlusion or ischemic optic neuropathy depending on the pattern and patient.
If instead the patient describes sudden monocular dimming, greying, or a curtain-like loss of vision that completely resolves over minutes, think about transient retinal ischemia (amaurosis fugax). This may represent a retinal TIA and requires urgent vascular assessment.
“Stars” after standing up
Brief bilateral greying, tunnel vision, or sparkling after standing quickly, especially with lightheadedness, heat, dehydration, or presyncope, may reflect systemic hypoperfusion.
Transient visual obscurations
Very brief greying or blacking out of vision triggered by posture change, bending, coughing, or straining, especially with headache or pulsatile tinnitus, should make you think about papilledema and raised intracranial pressure.
Shimmering zig-zags
Think migraine aura, especially if the phenomenon gradually expands and resolves.
Curtain or shadow
Think retinal detachment until proven otherwise.
The wording matters.
Trauma Changes the Story
Trauma gets its own post later in this series, but it matters here.
Flashes, floaters, reduced vision, or a field defect after trauma can reflect:
Do not bury the trauma history halfway through your questions.
Ask early.
The Exam You Need
Visual Acuity
Check each eye separately.
Again, normal central acuity does not rule out a peripheral retinal tear.
Pupils
Look for an RAPD.
A large retinal detachment or significant optic nerve lesion may produce one.
Confrontation Visual Fields
This becomes especially important if the patient reports:
Vitreous
At the slit lamp look for pigment or blood in the vitreous. Shafer’s sign, or “tobacco dust,” refers to pigment in the anterior vitreous and should raise concern for retinal tears in a patient with acute flashes and floaters. If you are Shafer’s positive and can’t find evidence of a retinal tear or detachment, it’s a good indication to check again. A vitreous haemorrhage should also raise concern for an underlying retinal tear.
Dilated Fundus Examination
This is the main event. At the slit lamp with a 90D or 78D lens, assess the vitreous, disc, macula, and vessels. With the indirect ophthalmoscope and a 20D or 28D lens assess the peripheral retina for tears, holes, or detachment. The periphery is your most likely location to find a tear, which will require scleral depression to appreciate.
A Practical Flashes & Floaters Approach
When someone reports flashes, floaters, or another visual disturbance:
1. Positive or negative?
Positive: flashes, floaters, sparkles, zig-zags.
Negative: curtain, shadow, field loss, greying, blackout.
2. One eye or both?
Monocular: think eye, vitreous, retina, optic nerve.
Binocular: consider migraine, neurologic disease, or systemic causes.
3. Sudden or gradual?
Sudden: retinal or vascular pathology becomes more concerning.
Gradually evolving over minutes: migraine aura becomes more likely.
4. Any retinal danger signs?
If yes, the peripheral retina needs a careful look.
If You Remember Nothing Else
Next month: Diplopia on Your Ophthalmology Elective
