OCT and ultrasound as complementary tests

Optical coherence tomography (OCT) analyses the layers of the retina at high resolution. It is particularly useful for studying the macular area and detecting vitreomacular traction. Ocular ultrasound (B-mode) is valuable when the ocular media are not very transparent (intravitreal haemorrhage, dense cataract): it makes it possible to visualise the retina and the vitreous without seeing directly into them.

Management according to the findings

If the examination is normal, monitoring is arranged: the patient is reviewed at 4 to 8 weeks to check the stability of the PVD, and informed of the signs that should prompt an urgent return. If a retinal tear without detachment is found, preventive laser treatment (photocoagulation) may be proposed to “weld” it to the wall of the eye and block the passage of subretinal fluid. If a retinal detachment is already established, surgery is required (vitrectomy or scleral buckle), as an emergency for recent forms involving the macula.

Key point

The dilated fundus examination is the only test that allows the retina to be seen in its entirety. It cannot be carried out by a general practitioner. In the event of new flashes, the ophthalmologist — not the general emergency department — is the right point of contact, or a specialised ophthalmological emergency service.

FREQUENTLY ASKED QUESTIONS

Frequently asked questions about phosphenes

Phosphenes and floaters: what is the difference?

A phosphene is a brief flash of light, often located at the periphery of the visual field. Floaters are mobile shadows — filaments, grey dots — that drift across the field of view. The two can occur together during a vitreous detachment: the vitreous pulls on the retina (flash) and at the same time releases opacities that cast shadows (floaters). See also: black spots that move around.

Are phosphenes dangerous?

The great majority of phosphenes are benign. They often accompany the natural ageing of the vitreous (posterior detachment) and fade over time. Less commonly, however, they can signal a retinal tear or detachment. A sudden onset of flashes, especially with a shower of floaters or a black veil, calls for a prompt ophthalmological consultation.

Is it normal to see flashes at night?

Phosphenes are often more visible in the dark, because the contrast makes them easier to perceive. Occasional flashes in the dark, during eye movements, can be linked to benign traction of the vitreous. New, frequent or intense flashes — even at night — always warrant a fundus examination to rule out a retinal cause.

Phosphenes and migraine: how do you tell them apart?

Phosphenes of retinal origin are brief flashes, often on one side only and at the periphery of the visual field, without progression or prolonged duration. Migraine with aura instead produces shimmering luminous zigzags, broken lines or a patch that gradually enlarges, affecting both eyes and lasting 15 to 30 minutes, sometimes followed by a headache. The cerebral (not retinal) origin of migraine explains the bilateral involvement.

When should you seek urgent care for flashes of light?

You should seek urgent care in the event of a sudden onset of many flashes, especially if they are accompanied by a shower of new floaters, a black veil or curtain in the visual field, or a drop in vision. These signs may reflect a retinal tear or detachment that must be managed without delay. The visual prognosis depends on how quickly treatment is provided.

Do phosphenes disappear over time?

Often, yes. Phosphenes linked to a vitreous detachment fade over a few weeks to a few months, as the vitreous finishes detaching and the traction ceases. This natural course does not remove the need for an initial examination: only a dilated fundus examination can rule out an associated retinal tear.

High myopia and phosphenes: is there more cause for concern?

Yes, vigilance is heightened. High myopia lengthens the eyeball and stretches the retina, making it more fragile at the periphery. People with high myopia undergo PVD earlier (from 40-45 years of age) and are at higher risk of a tear. Any new phosphene in a highly short-sighted person should lead to an ophthalmological examination within 24 to 48 hours. Regular fundus follow-up is recommended, even in the absence of symptoms.

Sources

  • French Society of Ophthalmology (SFO) — Data on the vitreous, posterior vitreous detachment, retinal tears and retinal detachment.
  • College of University Ophthalmologists of France (COUF) — Item “Vitreoretinal pathology: posterior vitreous detachment, retinal tear and retinal detachment”; semiology of phosphenes.
  • French National Authority for Health (HAS) — Guidance on the management of ophthalmological emergencies and functional ocular signs.
  • Ameli.fr (French Health Insurance) — Fact sheet “Retinal detachment: symptoms, causes and treatment”.

This article is for information only and does not replace a medical consultation. Flashes of light of sudden onset, associated with a shower of floaters or a black veil, constitute an ophthalmological emergency. Only a dilated fundus examination can rule out retinal involvement and establish a personalised diagnosis.

Recent flashes of light or visual disturbance?

Dr Moïse Tourabaly, former chief clinical fellow at the Quinze-Vingts hospital, carries out a full fundus examination and directs you towards the management best suited to your situation, at consultations in Cachan or Paris 13.

Book an appointment

Related articles

The dilated fundus examination: the reference test

The ophthalmologist examines the retina using a slit lamp and a three-mirror contact lens, or an indirect ophthalmoscope with a wide-field lens. This examination makes it possible to:

  • Visualise the state of the vitreous and its attachment zone (posterior hyaloid).
  • Detect any peripheral retinal tear.
  • Identify an area of fragility (lattice degeneration) before it tears.
  • Confirm or rule out an early retinal detachment.

OCT and ultrasound as complementary tests

Optical coherence tomography (OCT) analyses the layers of the retina at high resolution. It is particularly useful for studying the macular area and detecting vitreomacular traction. Ocular ultrasound (B-mode) is valuable when the ocular media are not very transparent (intravitreal haemorrhage, dense cataract): it makes it possible to visualise the retina and the vitreous without seeing directly into them.

Management according to the findings

If the examination is normal, monitoring is arranged: the patient is reviewed at 4 to 8 weeks to check the stability of the PVD, and informed of the signs that should prompt an urgent return. If a retinal tear without detachment is found, preventive laser treatment (photocoagulation) may be proposed to “weld” it to the wall of the eye and block the passage of subretinal fluid. If a retinal detachment is already established, surgery is required (vitrectomy or scleral buckle), as an emergency for recent forms involving the macula.

Key point

The dilated fundus examination is the only test that allows the retina to be seen in its entirety. It cannot be carried out by a general practitioner. In the event of new flashes, the ophthalmologist — not the general emergency department — is the right point of contact, or a specialised ophthalmological emergency service.

FREQUENTLY ASKED QUESTIONS

Frequently asked questions about phosphenes

Phosphenes and floaters: what is the difference?

A phosphene is a brief flash of light, often located at the periphery of the visual field. Floaters are mobile shadows — filaments, grey dots — that drift across the field of view. The two can occur together during a vitreous detachment: the vitreous pulls on the retina (flash) and at the same time releases opacities that cast shadows (floaters). See also: black spots that move around.

Are phosphenes dangerous?

The great majority of phosphenes are benign. They often accompany the natural ageing of the vitreous (posterior detachment) and fade over time. Less commonly, however, they can signal a retinal tear or detachment. A sudden onset of flashes, especially with a shower of floaters or a black veil, calls for a prompt ophthalmological consultation.

Is it normal to see flashes at night?

Phosphenes are often more visible in the dark, because the contrast makes them easier to perceive. Occasional flashes in the dark, during eye movements, can be linked to benign traction of the vitreous. New, frequent or intense flashes — even at night — always warrant a fundus examination to rule out a retinal cause.

Phosphenes and migraine: how do you tell them apart?

Phosphenes of retinal origin are brief flashes, often on one side only and at the periphery of the visual field, without progression or prolonged duration. Migraine with aura instead produces shimmering luminous zigzags, broken lines or a patch that gradually enlarges, affecting both eyes and lasting 15 to 30 minutes, sometimes followed by a headache. The cerebral (not retinal) origin of migraine explains the bilateral involvement.

When should you seek urgent care for flashes of light?

You should seek urgent care in the event of a sudden onset of many flashes, especially if they are accompanied by a shower of new floaters, a black veil or curtain in the visual field, or a drop in vision. These signs may reflect a retinal tear or detachment that must be managed without delay. The visual prognosis depends on how quickly treatment is provided.

Do phosphenes disappear over time?

Often, yes. Phosphenes linked to a vitreous detachment fade over a few weeks to a few months, as the vitreous finishes detaching and the traction ceases. This natural course does not remove the need for an initial examination: only a dilated fundus examination can rule out an associated retinal tear.

High myopia and phosphenes: is there more cause for concern?

Yes, vigilance is heightened. High myopia lengthens the eyeball and stretches the retina, making it more fragile at the periphery. People with high myopia undergo PVD earlier (from 40-45 years of age) and are at higher risk of a tear. Any new phosphene in a highly short-sighted person should lead to an ophthalmological examination within 24 to 48 hours. Regular fundus follow-up is recommended, even in the absence of symptoms.

Sources

  • French Society of Ophthalmology (SFO) — Data on the vitreous, posterior vitreous detachment, retinal tears and retinal detachment.
  • College of University Ophthalmologists of France (COUF) — Item “Vitreoretinal pathology: posterior vitreous detachment, retinal tear and retinal detachment”; semiology of phosphenes.
  • French National Authority for Health (HAS) — Guidance on the management of ophthalmological emergencies and functional ocular signs.
  • Ameli.fr (French Health Insurance) — Fact sheet “Retinal detachment: symptoms, causes and treatment”.

This article is for information only and does not replace a medical consultation. Flashes of light of sudden onset, associated with a shower of floaters or a black veil, constitute an ophthalmological emergency. Only a dilated fundus examination can rule out retinal involvement and establish a personalised diagnosis.

Recent flashes of light or visual disturbance?

Dr Moïse Tourabaly, former chief clinical fellow at the Quinze-Vingts hospital, carries out a full fundus examination and directs you towards the management best suited to your situation, at consultations in Cachan or Paris 13.

Book an appointment

Related articles

Serious causes: retinal tear and retinal detachment

More rarely, phosphenes can herald a retinal tear or detachment. A retinal tear lets fluid pass beneath the retina, which lifts away like wallpaper peeling off a wall. Gradually, the retina detaches from the wall of the eye over an ever-larger area. Without prompt treatment, retinal detachment can lead to irreversible loss of vision in the affected sector — and even to blindness if the macular area (responsible for fine central vision) is involved.

Certain factors increase the risk of a tear or detachment:

  • High myopia (beyond −6 dioptres): the elongated eye stretches the retina, making it more fragile at the periphery.
  • Ocular trauma: a blow to the eye or the skull.
  • Personal or family history of retinal detachment.
  • Previous eye surgery (cataract, refractive surgery).
  • Diabetic retinopathy: retinopathy related to diabetes weakens the blood vessels and the retina.

EMERGENCY

Warning signs: when to seek urgent care?

Some phosphenes warrant an emergency ophthalmological consultation within the following hours. The rule is simple: any sudden onset of flashes, especially if accompanied by other symptoms, should lead to a prompt examination of the retina. It is better to be seen unnecessarily than to miss a tear or an early detachment.

Seek urgent care if you notice any of these signs

  • Sudden appearance of many flashes of light, particularly to the sides or lower part of the visual field, especially if this is new.
  • Sudden shower of new floaters: dozens of small dots, filaments or a cloud of specks appearing within minutes.
  • Black veil or curtain masking part of the visual field (below, above or to the side), like a shadow that spreads.
  • Sudden drop in vision or distortion of straight lines (metamorphopsia).

These four signs — flashes, a shower of floaters, a black veil, a drop in vision — can signal a retinal detachment in progress. The visual prognosis depends directly on how quickly care is provided. Do not wait until the next day.

Conversely, an old, stable phosphene (for example, an isolated peripheral flash during eye movements, known for years) with no associated sign is generally benign. A first ophthalmological opinion nonetheless remains sensible, in particular to check the state of the peripheral retina.

DIAGNOSIS

Examinations and diagnosis of phosphenes

The diagnosis rests above all on a dilated fundus examination. After a precise history covering how long the flashes have been present, their frequency, the circumstances and any associated symptoms, the ophthalmologist instils drops that dilate the pupil. This makes it possible to explore the retina right out to its periphery, where tears and areas of fragility most often lie.

The dilated fundus examination: the reference test

The ophthalmologist examines the retina using a slit lamp and a three-mirror contact lens, or an indirect ophthalmoscope with a wide-field lens. This examination makes it possible to:

  • Visualise the state of the vitreous and its attachment zone (posterior hyaloid).
  • Detect any peripheral retinal tear.
  • Identify an area of fragility (lattice degeneration) before it tears.
  • Confirm or rule out an early retinal detachment.

OCT and ultrasound as complementary tests

Optical coherence tomography (OCT) analyses the layers of the retina at high resolution. It is particularly useful for studying the macular area and detecting vitreomacular traction. Ocular ultrasound (B-mode) is valuable when the ocular media are not very transparent (intravitreal haemorrhage, dense cataract): it makes it possible to visualise the retina and the vitreous without seeing directly into them.

Management according to the findings

If the examination is normal, monitoring is arranged: the patient is reviewed at 4 to 8 weeks to check the stability of the PVD, and informed of the signs that should prompt an urgent return. If a retinal tear without detachment is found, preventive laser treatment (photocoagulation) may be proposed to “weld” it to the wall of the eye and block the passage of subretinal fluid. If a retinal detachment is already established, surgery is required (vitrectomy or scleral buckle), as an emergency for recent forms involving the macula.

Key point

The dilated fundus examination is the only test that allows the retina to be seen in its entirety. It cannot be carried out by a general practitioner. In the event of new flashes, the ophthalmologist — not the general emergency department — is the right point of contact, or a specialised ophthalmological emergency service.

FREQUENTLY ASKED QUESTIONS

Frequently asked questions about phosphenes

Phosphenes and floaters: what is the difference?

A phosphene is a brief flash of light, often located at the periphery of the visual field. Floaters are mobile shadows — filaments, grey dots — that drift across the field of view. The two can occur together during a vitreous detachment: the vitreous pulls on the retina (flash) and at the same time releases opacities that cast shadows (floaters). See also: black spots that move around.

Are phosphenes dangerous?

The great majority of phosphenes are benign. They often accompany the natural ageing of the vitreous (posterior detachment) and fade over time. Less commonly, however, they can signal a retinal tear or detachment. A sudden onset of flashes, especially with a shower of floaters or a black veil, calls for a prompt ophthalmological consultation.

Is it normal to see flashes at night?

Phosphenes are often more visible in the dark, because the contrast makes them easier to perceive. Occasional flashes in the dark, during eye movements, can be linked to benign traction of the vitreous. New, frequent or intense flashes — even at night — always warrant a fundus examination to rule out a retinal cause.

Phosphenes and migraine: how do you tell them apart?

Phosphenes of retinal origin are brief flashes, often on one side only and at the periphery of the visual field, without progression or prolonged duration. Migraine with aura instead produces shimmering luminous zigzags, broken lines or a patch that gradually enlarges, affecting both eyes and lasting 15 to 30 minutes, sometimes followed by a headache. The cerebral (not retinal) origin of migraine explains the bilateral involvement.

When should you seek urgent care for flashes of light?

You should seek urgent care in the event of a sudden onset of many flashes, especially if they are accompanied by a shower of new floaters, a black veil or curtain in the visual field, or a drop in vision. These signs may reflect a retinal tear or detachment that must be managed without delay. The visual prognosis depends on how quickly treatment is provided.

Do phosphenes disappear over time?

Often, yes. Phosphenes linked to a vitreous detachment fade over a few weeks to a few months, as the vitreous finishes detaching and the traction ceases. This natural course does not remove the need for an initial examination: only a dilated fundus examination can rule out an associated retinal tear.

High myopia and phosphenes: is there more cause for concern?

Yes, vigilance is heightened. High myopia lengthens the eyeball and stretches the retina, making it more fragile at the periphery. People with high myopia undergo PVD earlier (from 40-45 years of age) and are at higher risk of a tear. Any new phosphene in a highly short-sighted person should lead to an ophthalmological examination within 24 to 48 hours. Regular fundus follow-up is recommended, even in the absence of symptoms.

Sources

  • French Society of Ophthalmology (SFO) — Data on the vitreous, posterior vitreous detachment, retinal tears and retinal detachment.
  • College of University Ophthalmologists of France (COUF) — Item “Vitreoretinal pathology: posterior vitreous detachment, retinal tear and retinal detachment”; semiology of phosphenes.
  • French National Authority for Health (HAS) — Guidance on the management of ophthalmological emergencies and functional ocular signs.
  • Ameli.fr (French Health Insurance) — Fact sheet “Retinal detachment: symptoms, causes and treatment”.

This article is for information only and does not replace a medical consultation. Flashes of light of sudden onset, associated with a shower of floaters or a black veil, constitute an ophthalmological emergency. Only a dilated fundus examination can rule out retinal involvement and establish a personalised diagnosis.

Recent flashes of light or visual disturbance?

Dr Moïse Tourabaly, former chief clinical fellow at the Quinze-Vingts hospital, carries out a full fundus examination and directs you towards the management best suited to your situation, at consultations in Cachan or Paris 13.

Book an appointment

Related articles

Posterior vitreous detachment: common, usually benign

With age, the vitreous — the clear gel that fills the back two-thirds of the eye — gradually liquefies and shrinks. It eventually separates from the retina: this is posterior vitreous detachment (PVD). This phenomenon occurs in most people after the age of 60, and earlier in those with high myopia. During the active phase of detachment, the pulling of the vitreous on the retina generates phosphenes, often together with the sudden appearance of new floaters. See the dedicated article on vitreous detachment.

In the great majority of cases, PVD is a benign physiological phenomenon. However, in around 10 to 15% of symptomatic PVDs, the detaching vitreous tears away a fragment of retina with it, creating a break. This is why any symptomatic PVD (flashes + new floaters) warrants an eye examination within the following days to check that the retina is intact.

Serious causes: retinal tear and retinal detachment

More rarely, phosphenes can herald a retinal tear or detachment. A retinal tear lets fluid pass beneath the retina, which lifts away like wallpaper peeling off a wall. Gradually, the retina detaches from the wall of the eye over an ever-larger area. Without prompt treatment, retinal detachment can lead to irreversible loss of vision in the affected sector — and even to blindness if the macular area (responsible for fine central vision) is involved.

Certain factors increase the risk of a tear or detachment:

  • High myopia (beyond −6 dioptres): the elongated eye stretches the retina, making it more fragile at the periphery.
  • Ocular trauma: a blow to the eye or the skull.
  • Personal or family history of retinal detachment.
  • Previous eye surgery (cataract, refractive surgery).
  • Diabetic retinopathy: retinopathy related to diabetes weakens the blood vessels and the retina.

EMERGENCY

Warning signs: when to seek urgent care?

Some phosphenes warrant an emergency ophthalmological consultation within the following hours. The rule is simple: any sudden onset of flashes, especially if accompanied by other symptoms, should lead to a prompt examination of the retina. It is better to be seen unnecessarily than to miss a tear or an early detachment.

Seek urgent care if you notice any of these signs

  • Sudden appearance of many flashes of light, particularly to the sides or lower part of the visual field, especially if this is new.
  • Sudden shower of new floaters: dozens of small dots, filaments or a cloud of specks appearing within minutes.
  • Black veil or curtain masking part of the visual field (below, above or to the side), like a shadow that spreads.
  • Sudden drop in vision or distortion of straight lines (metamorphopsia).

These four signs — flashes, a shower of floaters, a black veil, a drop in vision — can signal a retinal detachment in progress. The visual prognosis depends directly on how quickly care is provided. Do not wait until the next day.

Conversely, an old, stable phosphene (for example, an isolated peripheral flash during eye movements, known for years) with no associated sign is generally benign. A first ophthalmological opinion nonetheless remains sensible, in particular to check the state of the peripheral retina.

DIAGNOSIS

Examinations and diagnosis of phosphenes

The diagnosis rests above all on a dilated fundus examination. After a precise history covering how long the flashes have been present, their frequency, the circumstances and any associated symptoms, the ophthalmologist instils drops that dilate the pupil. This makes it possible to explore the retina right out to its periphery, where tears and areas of fragility most often lie.

The dilated fundus examination: the reference test

The ophthalmologist examines the retina using a slit lamp and a three-mirror contact lens, or an indirect ophthalmoscope with a wide-field lens. This examination makes it possible to:

  • Visualise the state of the vitreous and its attachment zone (posterior hyaloid).
  • Detect any peripheral retinal tear.
  • Identify an area of fragility (lattice degeneration) before it tears.
  • Confirm or rule out an early retinal detachment.

OCT and ultrasound as complementary tests

Optical coherence tomography (OCT) analyses the layers of the retina at high resolution. It is particularly useful for studying the macular area and detecting vitreomacular traction. Ocular ultrasound (B-mode) is valuable when the ocular media are not very transparent (intravitreal haemorrhage, dense cataract): it makes it possible to visualise the retina and the vitreous without seeing directly into them.

Management according to the findings

If the examination is normal, monitoring is arranged: the patient is reviewed at 4 to 8 weeks to check the stability of the PVD, and informed of the signs that should prompt an urgent return. If a retinal tear without detachment is found, preventive laser treatment (photocoagulation) may be proposed to “weld” it to the wall of the eye and block the passage of subretinal fluid. If a retinal detachment is already established, surgery is required (vitrectomy or scleral buckle), as an emergency for recent forms involving the macula.

Key point

The dilated fundus examination is the only test that allows the retina to be seen in its entirety. It cannot be carried out by a general practitioner. In the event of new flashes, the ophthalmologist — not the general emergency department — is the right point of contact, or a specialised ophthalmological emergency service.

FREQUENTLY ASKED QUESTIONS

Frequently asked questions about phosphenes

Phosphenes and floaters: what is the difference?

A phosphene is a brief flash of light, often located at the periphery of the visual field. Floaters are mobile shadows — filaments, grey dots — that drift across the field of view. The two can occur together during a vitreous detachment: the vitreous pulls on the retina (flash) and at the same time releases opacities that cast shadows (floaters). See also: black spots that move around.

Are phosphenes dangerous?

The great majority of phosphenes are benign. They often accompany the natural ageing of the vitreous (posterior detachment) and fade over time. Less commonly, however, they can signal a retinal tear or detachment. A sudden onset of flashes, especially with a shower of floaters or a black veil, calls for a prompt ophthalmological consultation.

Is it normal to see flashes at night?

Phosphenes are often more visible in the dark, because the contrast makes them easier to perceive. Occasional flashes in the dark, during eye movements, can be linked to benign traction of the vitreous. New, frequent or intense flashes — even at night — always warrant a fundus examination to rule out a retinal cause.

Phosphenes and migraine: how do you tell them apart?

Phosphenes of retinal origin are brief flashes, often on one side only and at the periphery of the visual field, without progression or prolonged duration. Migraine with aura instead produces shimmering luminous zigzags, broken lines or a patch that gradually enlarges, affecting both eyes and lasting 15 to 30 minutes, sometimes followed by a headache. The cerebral (not retinal) origin of migraine explains the bilateral involvement.

When should you seek urgent care for flashes of light?

You should seek urgent care in the event of a sudden onset of many flashes, especially if they are accompanied by a shower of new floaters, a black veil or curtain in the visual field, or a drop in vision. These signs may reflect a retinal tear or detachment that must be managed without delay. The visual prognosis depends on how quickly treatment is provided.

Do phosphenes disappear over time?

Often, yes. Phosphenes linked to a vitreous detachment fade over a few weeks to a few months, as the vitreous finishes detaching and the traction ceases. This natural course does not remove the need for an initial examination: only a dilated fundus examination can rule out an associated retinal tear.

High myopia and phosphenes: is there more cause for concern?

Yes, vigilance is heightened. High myopia lengthens the eyeball and stretches the retina, making it more fragile at the periphery. People with high myopia undergo PVD earlier (from 40-45 years of age) and are at higher risk of a tear. Any new phosphene in a highly short-sighted person should lead to an ophthalmological examination within 24 to 48 hours. Regular fundus follow-up is recommended, even in the absence of symptoms.

Sources

  • French Society of Ophthalmology (SFO) — Data on the vitreous, posterior vitreous detachment, retinal tears and retinal detachment.
  • College of University Ophthalmologists of France (COUF) — Item “Vitreoretinal pathology: posterior vitreous detachment, retinal tear and retinal detachment”; semiology of phosphenes.
  • French National Authority for Health (HAS) — Guidance on the management of ophthalmological emergencies and functional ocular signs.
  • Ameli.fr (French Health Insurance) — Fact sheet “Retinal detachment: symptoms, causes and treatment”.

This article is for information only and does not replace a medical consultation. Flashes of light of sudden onset, associated with a shower of floaters or a black veil, constitute an ophthalmological emergency. Only a dilated fundus examination can rule out retinal involvement and establish a personalised diagnosis.

Recent flashes of light or visual disturbance?

Dr Moïse Tourabaly, former chief clinical fellow at the Quinze-Vingts hospital, carries out a full fundus examination and directs you towards the management best suited to your situation, at consultations in Cachan or Paris 13.

Book an appointment

Related articles

Benign causes: pressure and ophthalmic migraine

Mechanical compression of the retina. Rubbing the eyes, intense physical effort (coughing, sneezing, blowing the nose) or a rapid change in head position can momentarily exert pressure on the eyeball or gently pull on the retina. These phosphenes are fleeting, one-sided and do not recur in a worrying way. They are perfectly benign.

Migraine with aura (formerly called “ophthalmic migraine”) causes light sensations of cerebral rather than retinal origin. They typically take the form of shimmering luminous zigzags, broken lines or a patch that gradually enlarges into a “horseshoe” shape. These episodes usually last 15 to 30 minutes, affect both eyes at once (involvement of the visual cortex, not the eye) and may be followed by a headache. Their gradual, bilateral pattern clearly distinguishes them from the brief, one-sided flashes of retinal origin. Migraine with aura is benign as far as vision is concerned, but it warrants neurological follow-up.

Orthostatic hypotension. Standing up too quickly, a sudden drop in blood pressure can cause a few seconds of “diffuse phosphenes” together with mild dizziness. These episodes do not involve the retina and fade as soon as circulation is restored.

Posterior vitreous detachment: common, usually benign

With age, the vitreous — the clear gel that fills the back two-thirds of the eye — gradually liquefies and shrinks. It eventually separates from the retina: this is posterior vitreous detachment (PVD). This phenomenon occurs in most people after the age of 60, and earlier in those with high myopia. During the active phase of detachment, the pulling of the vitreous on the retina generates phosphenes, often together with the sudden appearance of new floaters. See the dedicated article on vitreous detachment.

In the great majority of cases, PVD is a benign physiological phenomenon. However, in around 10 to 15% of symptomatic PVDs, the detaching vitreous tears away a fragment of retina with it, creating a break. This is why any symptomatic PVD (flashes + new floaters) warrants an eye examination within the following days to check that the retina is intact.

Serious causes: retinal tear and retinal detachment

More rarely, phosphenes can herald a retinal tear or detachment. A retinal tear lets fluid pass beneath the retina, which lifts away like wallpaper peeling off a wall. Gradually, the retina detaches from the wall of the eye over an ever-larger area. Without prompt treatment, retinal detachment can lead to irreversible loss of vision in the affected sector — and even to blindness if the macular area (responsible for fine central vision) is involved.

Certain factors increase the risk of a tear or detachment:

  • High myopia (beyond −6 dioptres): the elongated eye stretches the retina, making it more fragile at the periphery.
  • Ocular trauma: a blow to the eye or the skull.
  • Personal or family history of retinal detachment.
  • Previous eye surgery (cataract, refractive surgery).
  • Diabetic retinopathy: retinopathy related to diabetes weakens the blood vessels and the retina.

EMERGENCY

Warning signs: when to seek urgent care?

Some phosphenes warrant an emergency ophthalmological consultation within the following hours. The rule is simple: any sudden onset of flashes, especially if accompanied by other symptoms, should lead to a prompt examination of the retina. It is better to be seen unnecessarily than to miss a tear or an early detachment.

Seek urgent care if you notice any of these signs

  • Sudden appearance of many flashes of light, particularly to the sides or lower part of the visual field, especially if this is new.
  • Sudden shower of new floaters: dozens of small dots, filaments or a cloud of specks appearing within minutes.
  • Black veil or curtain masking part of the visual field (below, above or to the side), like a shadow that spreads.
  • Sudden drop in vision or distortion of straight lines (metamorphopsia).

These four signs — flashes, a shower of floaters, a black veil, a drop in vision — can signal a retinal detachment in progress. The visual prognosis depends directly on how quickly care is provided. Do not wait until the next day.

Conversely, an old, stable phosphene (for example, an isolated peripheral flash during eye movements, known for years) with no associated sign is generally benign. A first ophthalmological opinion nonetheless remains sensible, in particular to check the state of the peripheral retina.

DIAGNOSIS

Examinations and diagnosis of phosphenes

The diagnosis rests above all on a dilated fundus examination. After a precise history covering how long the flashes have been present, their frequency, the circumstances and any associated symptoms, the ophthalmologist instils drops that dilate the pupil. This makes it possible to explore the retina right out to its periphery, where tears and areas of fragility most often lie.

The dilated fundus examination: the reference test

The ophthalmologist examines the retina using a slit lamp and a three-mirror contact lens, or an indirect ophthalmoscope with a wide-field lens. This examination makes it possible to:

  • Visualise the state of the vitreous and its attachment zone (posterior hyaloid).
  • Detect any peripheral retinal tear.
  • Identify an area of fragility (lattice degeneration) before it tears.
  • Confirm or rule out an early retinal detachment.

OCT and ultrasound as complementary tests

Optical coherence tomography (OCT) analyses the layers of the retina at high resolution. It is particularly useful for studying the macular area and detecting vitreomacular traction. Ocular ultrasound (B-mode) is valuable when the ocular media are not very transparent (intravitreal haemorrhage, dense cataract): it makes it possible to visualise the retina and the vitreous without seeing directly into them.

Management according to the findings

If the examination is normal, monitoring is arranged: the patient is reviewed at 4 to 8 weeks to check the stability of the PVD, and informed of the signs that should prompt an urgent return. If a retinal tear without detachment is found, preventive laser treatment (photocoagulation) may be proposed to “weld” it to the wall of the eye and block the passage of subretinal fluid. If a retinal detachment is already established, surgery is required (vitrectomy or scleral buckle), as an emergency for recent forms involving the macula.

Key point

The dilated fundus examination is the only test that allows the retina to be seen in its entirety. It cannot be carried out by a general practitioner. In the event of new flashes, the ophthalmologist — not the general emergency department — is the right point of contact, or a specialised ophthalmological emergency service.

FREQUENTLY ASKED QUESTIONS

Frequently asked questions about phosphenes

Phosphenes and floaters: what is the difference?

A phosphene is a brief flash of light, often located at the periphery of the visual field. Floaters are mobile shadows — filaments, grey dots — that drift across the field of view. The two can occur together during a vitreous detachment: the vitreous pulls on the retina (flash) and at the same time releases opacities that cast shadows (floaters). See also: black spots that move around.

Are phosphenes dangerous?

The great majority of phosphenes are benign. They often accompany the natural ageing of the vitreous (posterior detachment) and fade over time. Less commonly, however, they can signal a retinal tear or detachment. A sudden onset of flashes, especially with a shower of floaters or a black veil, calls for a prompt ophthalmological consultation.

Is it normal to see flashes at night?

Phosphenes are often more visible in the dark, because the contrast makes them easier to perceive. Occasional flashes in the dark, during eye movements, can be linked to benign traction of the vitreous. New, frequent or intense flashes — even at night — always warrant a fundus examination to rule out a retinal cause.

Phosphenes and migraine: how do you tell them apart?

Phosphenes of retinal origin are brief flashes, often on one side only and at the periphery of the visual field, without progression or prolonged duration. Migraine with aura instead produces shimmering luminous zigzags, broken lines or a patch that gradually enlarges, affecting both eyes and lasting 15 to 30 minutes, sometimes followed by a headache. The cerebral (not retinal) origin of migraine explains the bilateral involvement.

When should you seek urgent care for flashes of light?

You should seek urgent care in the event of a sudden onset of many flashes, especially if they are accompanied by a shower of new floaters, a black veil or curtain in the visual field, or a drop in vision. These signs may reflect a retinal tear or detachment that must be managed without delay. The visual prognosis depends on how quickly treatment is provided.

Do phosphenes disappear over time?

Often, yes. Phosphenes linked to a vitreous detachment fade over a few weeks to a few months, as the vitreous finishes detaching and the traction ceases. This natural course does not remove the need for an initial examination: only a dilated fundus examination can rule out an associated retinal tear.

High myopia and phosphenes: is there more cause for concern?

Yes, vigilance is heightened. High myopia lengthens the eyeball and stretches the retina, making it more fragile at the periphery. People with high myopia undergo PVD earlier (from 40-45 years of age) and are at higher risk of a tear. Any new phosphene in a highly short-sighted person should lead to an ophthalmological examination within 24 to 48 hours. Regular fundus follow-up is recommended, even in the absence of symptoms.

Sources

  • French Society of Ophthalmology (SFO) — Data on the vitreous, posterior vitreous detachment, retinal tears and retinal detachment.
  • College of University Ophthalmologists of France (COUF) — Item “Vitreoretinal pathology: posterior vitreous detachment, retinal tear and retinal detachment”; semiology of phosphenes.
  • French National Authority for Health (HAS) — Guidance on the management of ophthalmological emergencies and functional ocular signs.
  • Ameli.fr (French Health Insurance) — Fact sheet “Retinal detachment: symptoms, causes and treatment”.

This article is for information only and does not replace a medical consultation. Flashes of light of sudden onset, associated with a shower of floaters or a black veil, constitute an ophthalmological emergency. Only a dilated fundus examination can rule out retinal involvement and establish a personalised diagnosis.

Recent flashes of light or visual disturbance?

Dr Moïse Tourabaly, former chief clinical fellow at the Quinze-Vingts hospital, carries out a full fundus examination and directs you towards the management best suited to your situation, at consultations in Cachan or Paris 13.

Book an appointment

Related articles

Phosphenes, floaters and haloes: don’t confuse them

Phosphenes must be distinguished from three other visual phenomena that are often confused with them:

  • Floaters (also called flies or “black spots that move around”) are mobile shadows, filaments or grey dots that drift across the field of view. They correspond to opacities within the vitreous. They are covered in a dedicated article: black spots that move around.
  • Light haloes are rings or circles of light seen around light sources (headlights, street lamps). They often signal a problem with the cornea or the lens. See the article on light haloes.
  • Phosphenes are internal flashes or flickers, not linked to any external source. They can coexist with floaters during a vitreous detachment.

CAUSES

Benign and serious causes of phosphenes

Most phosphenes have a mechanical origin: pressure or traction on the retina generates a stimulation that the brain interprets as light. Others can have a neurological origin (migraine) or a circulatory one. The seriousness depends essentially on the underlying cause.

Benign causes: pressure and ophthalmic migraine

Mechanical compression of the retina. Rubbing the eyes, intense physical effort (coughing, sneezing, blowing the nose) or a rapid change in head position can momentarily exert pressure on the eyeball or gently pull on the retina. These phosphenes are fleeting, one-sided and do not recur in a worrying way. They are perfectly benign.

Migraine with aura (formerly called “ophthalmic migraine”) causes light sensations of cerebral rather than retinal origin. They typically take the form of shimmering luminous zigzags, broken lines or a patch that gradually enlarges into a “horseshoe” shape. These episodes usually last 15 to 30 minutes, affect both eyes at once (involvement of the visual cortex, not the eye) and may be followed by a headache. Their gradual, bilateral pattern clearly distinguishes them from the brief, one-sided flashes of retinal origin. Migraine with aura is benign as far as vision is concerned, but it warrants neurological follow-up.

Orthostatic hypotension. Standing up too quickly, a sudden drop in blood pressure can cause a few seconds of “diffuse phosphenes” together with mild dizziness. These episodes do not involve the retina and fade as soon as circulation is restored.

Posterior vitreous detachment: common, usually benign

With age, the vitreous — the clear gel that fills the back two-thirds of the eye — gradually liquefies and shrinks. It eventually separates from the retina: this is posterior vitreous detachment (PVD). This phenomenon occurs in most people after the age of 60, and earlier in those with high myopia. During the active phase of detachment, the pulling of the vitreous on the retina generates phosphenes, often together with the sudden appearance of new floaters. See the dedicated article on vitreous detachment.

In the great majority of cases, PVD is a benign physiological phenomenon. However, in around 10 to 15% of symptomatic PVDs, the detaching vitreous tears away a fragment of retina with it, creating a break. This is why any symptomatic PVD (flashes + new floaters) warrants an eye examination within the following days to check that the retina is intact.

Serious causes: retinal tear and retinal detachment

More rarely, phosphenes can herald a retinal tear or detachment. A retinal tear lets fluid pass beneath the retina, which lifts away like wallpaper peeling off a wall. Gradually, the retina detaches from the wall of the eye over an ever-larger area. Without prompt treatment, retinal detachment can lead to irreversible loss of vision in the affected sector — and even to blindness if the macular area (responsible for fine central vision) is involved.

Certain factors increase the risk of a tear or detachment:

  • High myopia (beyond −6 dioptres): the elongated eye stretches the retina, making it more fragile at the periphery.
  • Ocular trauma: a blow to the eye or the skull.
  • Personal or family history of retinal detachment.
  • Previous eye surgery (cataract, refractive surgery).
  • Diabetic retinopathy: retinopathy related to diabetes weakens the blood vessels and the retina.

EMERGENCY

Warning signs: when to seek urgent care?

Some phosphenes warrant an emergency ophthalmological consultation within the following hours. The rule is simple: any sudden onset of flashes, especially if accompanied by other symptoms, should lead to a prompt examination of the retina. It is better to be seen unnecessarily than to miss a tear or an early detachment.

Seek urgent care if you notice any of these signs

  • Sudden appearance of many flashes of light, particularly to the sides or lower part of the visual field, especially if this is new.
  • Sudden shower of new floaters: dozens of small dots, filaments or a cloud of specks appearing within minutes.
  • Black veil or curtain masking part of the visual field (below, above or to the side), like a shadow that spreads.
  • Sudden drop in vision or distortion of straight lines (metamorphopsia).

These four signs — flashes, a shower of floaters, a black veil, a drop in vision — can signal a retinal detachment in progress. The visual prognosis depends directly on how quickly care is provided. Do not wait until the next day.

Conversely, an old, stable phosphene (for example, an isolated peripheral flash during eye movements, known for years) with no associated sign is generally benign. A first ophthalmological opinion nonetheless remains sensible, in particular to check the state of the peripheral retina.

DIAGNOSIS

Examinations and diagnosis of phosphenes

The diagnosis rests above all on a dilated fundus examination. After a precise history covering how long the flashes have been present, their frequency, the circumstances and any associated symptoms, the ophthalmologist instils drops that dilate the pupil. This makes it possible to explore the retina right out to its periphery, where tears and areas of fragility most often lie.

The dilated fundus examination: the reference test

The ophthalmologist examines the retina using a slit lamp and a three-mirror contact lens, or an indirect ophthalmoscope with a wide-field lens. This examination makes it possible to:

  • Visualise the state of the vitreous and its attachment zone (posterior hyaloid).
  • Detect any peripheral retinal tear.
  • Identify an area of fragility (lattice degeneration) before it tears.
  • Confirm or rule out an early retinal detachment.

OCT and ultrasound as complementary tests

Optical coherence tomography (OCT) analyses the layers of the retina at high resolution. It is particularly useful for studying the macular area and detecting vitreomacular traction. Ocular ultrasound (B-mode) is valuable when the ocular media are not very transparent (intravitreal haemorrhage, dense cataract): it makes it possible to visualise the retina and the vitreous without seeing directly into them.

Management according to the findings

If the examination is normal, monitoring is arranged: the patient is reviewed at 4 to 8 weeks to check the stability of the PVD, and informed of the signs that should prompt an urgent return. If a retinal tear without detachment is found, preventive laser treatment (photocoagulation) may be proposed to “weld” it to the wall of the eye and block the passage of subretinal fluid. If a retinal detachment is already established, surgery is required (vitrectomy or scleral buckle), as an emergency for recent forms involving the macula.

Key point

The dilated fundus examination is the only test that allows the retina to be seen in its entirety. It cannot be carried out by a general practitioner. In the event of new flashes, the ophthalmologist — not the general emergency department — is the right point of contact, or a specialised ophthalmological emergency service.

FREQUENTLY ASKED QUESTIONS

Frequently asked questions about phosphenes

Phosphenes and floaters: what is the difference?

A phosphene is a brief flash of light, often located at the periphery of the visual field. Floaters are mobile shadows — filaments, grey dots — that drift across the field of view. The two can occur together during a vitreous detachment: the vitreous pulls on the retina (flash) and at the same time releases opacities that cast shadows (floaters). See also: black spots that move around.

Are phosphenes dangerous?

The great majority of phosphenes are benign. They often accompany the natural ageing of the vitreous (posterior detachment) and fade over time. Less commonly, however, they can signal a retinal tear or detachment. A sudden onset of flashes, especially with a shower of floaters or a black veil, calls for a prompt ophthalmological consultation.

Is it normal to see flashes at night?

Phosphenes are often more visible in the dark, because the contrast makes them easier to perceive. Occasional flashes in the dark, during eye movements, can be linked to benign traction of the vitreous. New, frequent or intense flashes — even at night — always warrant a fundus examination to rule out a retinal cause.

Phosphenes and migraine: how do you tell them apart?

Phosphenes of retinal origin are brief flashes, often on one side only and at the periphery of the visual field, without progression or prolonged duration. Migraine with aura instead produces shimmering luminous zigzags, broken lines or a patch that gradually enlarges, affecting both eyes and lasting 15 to 30 minutes, sometimes followed by a headache. The cerebral (not retinal) origin of migraine explains the bilateral involvement.

When should you seek urgent care for flashes of light?

You should seek urgent care in the event of a sudden onset of many flashes, especially if they are accompanied by a shower of new floaters, a black veil or curtain in the visual field, or a drop in vision. These signs may reflect a retinal tear or detachment that must be managed without delay. The visual prognosis depends on how quickly treatment is provided.

Do phosphenes disappear over time?

Often, yes. Phosphenes linked to a vitreous detachment fade over a few weeks to a few months, as the vitreous finishes detaching and the traction ceases. This natural course does not remove the need for an initial examination: only a dilated fundus examination can rule out an associated retinal tear.

High myopia and phosphenes: is there more cause for concern?

Yes, vigilance is heightened. High myopia lengthens the eyeball and stretches the retina, making it more fragile at the periphery. People with high myopia undergo PVD earlier (from 40-45 years of age) and are at higher risk of a tear. Any new phosphene in a highly short-sighted person should lead to an ophthalmological examination within 24 to 48 hours. Regular fundus follow-up is recommended, even in the absence of symptoms.

Sources

  • French Society of Ophthalmology (SFO) — Data on the vitreous, posterior vitreous detachment, retinal tears and retinal detachment.
  • College of University Ophthalmologists of France (COUF) — Item “Vitreoretinal pathology: posterior vitreous detachment, retinal tear and retinal detachment”; semiology of phosphenes.
  • French National Authority for Health (HAS) — Guidance on the management of ophthalmological emergencies and functional ocular signs.
  • Ameli.fr (French Health Insurance) — Fact sheet “Retinal detachment: symptoms, causes and treatment”.

This article is for information only and does not replace a medical consultation. Flashes of light of sudden onset, associated with a shower of floaters or a black veil, constitute an ophthalmological emergency. Only a dilated fundus examination can rule out retinal involvement and establish a personalised diagnosis.

Recent flashes of light or visual disturbance?

Dr Moïse Tourabaly, former chief clinical fellow at the Quinze-Vingts hospital, carries out a full fundus examination and directs you towards the management best suited to your situation, at consultations in Cachan or Paris 13.

Book an appointment

Related articles

Phosphenes: those flashes of light in the visual field

Phosphenes are light sensations — flashes, flickers, sparks — perceived by the eye without any real light source causing them. Most often benign and linked to the natural ageing of the vitreous, they can sometimes signal a retinal emergency. Understanding their origin, telling the harmless from the serious, and knowing the warning signs that call for prompt medical attention: here is what every patient should know.

UNDERSTANDING

What is a phosphene?

A phosphene is the perception of a light signal — a flash, flicker, spark or arc of light — when no light actually reaches the eye. This sensation arises from a mechanical or electrical stimulation of the retina, which sends the brain a message it interprets as light. The word comes from the Greek phos (light) and phainein (to appear).

Everyone has experienced a harmless phosphene: the bright spots that appear when you rub your eyes, or the brief flash felt after a mild knock. These occasional phenomena are not serious. What deserves attention are phosphenes that are new, repeated or persistent, especially after the age of 50 or in a short-sighted patient.

Phosphenes stand out through several features. They are often more visible in the dark or during rapid eye movements. They usually appear at the edges of the visual field (to the sides, above or below), rather than in the centre. Their duration is brief — a fraction of a second to a few seconds — unlike visual hallucinations, which persist.

Phosphenes, floaters and haloes: don’t confuse them

Phosphenes must be distinguished from three other visual phenomena that are often confused with them:

  • Floaters (also called flies or “black spots that move around”) are mobile shadows, filaments or grey dots that drift across the field of view. They correspond to opacities within the vitreous. They are covered in a dedicated article: black spots that move around.
  • Light haloes are rings or circles of light seen around light sources (headlights, street lamps). They often signal a problem with the cornea or the lens. See the article on light haloes.
  • Phosphenes are internal flashes or flickers, not linked to any external source. They can coexist with floaters during a vitreous detachment.

CAUSES

Benign and serious causes of phosphenes

Most phosphenes have a mechanical origin: pressure or traction on the retina generates a stimulation that the brain interprets as light. Others can have a neurological origin (migraine) or a circulatory one. The seriousness depends essentially on the underlying cause.

Benign causes: pressure and ophthalmic migraine

Mechanical compression of the retina. Rubbing the eyes, intense physical effort (coughing, sneezing, blowing the nose) or a rapid change in head position can momentarily exert pressure on the eyeball or gently pull on the retina. These phosphenes are fleeting, one-sided and do not recur in a worrying way. They are perfectly benign.

Migraine with aura (formerly called “ophthalmic migraine”) causes light sensations of cerebral rather than retinal origin. They typically take the form of shimmering luminous zigzags, broken lines or a patch that gradually enlarges into a “horseshoe” shape. These episodes usually last 15 to 30 minutes, affect both eyes at once (involvement of the visual cortex, not the eye) and may be followed by a headache. Their gradual, bilateral pattern clearly distinguishes them from the brief, one-sided flashes of retinal origin. Migraine with aura is benign as far as vision is concerned, but it warrants neurological follow-up.

Orthostatic hypotension. Standing up too quickly, a sudden drop in blood pressure can cause a few seconds of “diffuse phosphenes” together with mild dizziness. These episodes do not involve the retina and fade as soon as circulation is restored.

Posterior vitreous detachment: common, usually benign

With age, the vitreous — the clear gel that fills the back two-thirds of the eye — gradually liquefies and shrinks. It eventually separates from the retina: this is posterior vitreous detachment (PVD). This phenomenon occurs in most people after the age of 60, and earlier in those with high myopia. During the active phase of detachment, the pulling of the vitreous on the retina generates phosphenes, often together with the sudden appearance of new floaters. See the dedicated article on vitreous detachment.

In the great majority of cases, PVD is a benign physiological phenomenon. However, in around 10 to 15% of symptomatic PVDs, the detaching vitreous tears away a fragment of retina with it, creating a break. This is why any symptomatic PVD (flashes + new floaters) warrants an eye examination within the following days to check that the retina is intact.

Serious causes: retinal tear and retinal detachment

More rarely, phosphenes can herald a retinal tear or detachment. A retinal tear lets fluid pass beneath the retina, which lifts away like wallpaper peeling off a wall. Gradually, the retina detaches from the wall of the eye over an ever-larger area. Without prompt treatment, retinal detachment can lead to irreversible loss of vision in the affected sector — and even to blindness if the macular area (responsible for fine central vision) is involved.

Certain factors increase the risk of a tear or detachment:

  • High myopia (beyond −6 dioptres): the elongated eye stretches the retina, making it more fragile at the periphery.
  • Ocular trauma: a blow to the eye or the skull.
  • Personal or family history of retinal detachment.
  • Previous eye surgery (cataract, refractive surgery).
  • Diabetic retinopathy: retinopathy related to diabetes weakens the blood vessels and the retina.

EMERGENCY

Warning signs: when to seek urgent care?

Some phosphenes warrant an emergency ophthalmological consultation within the following hours. The rule is simple: any sudden onset of flashes, especially if accompanied by other symptoms, should lead to a prompt examination of the retina. It is better to be seen unnecessarily than to miss a tear or an early detachment.

Seek urgent care if you notice any of these signs

  • Sudden appearance of many flashes of light, particularly to the sides or lower part of the visual field, especially if this is new.
  • Sudden shower of new floaters: dozens of small dots, filaments or a cloud of specks appearing within minutes.
  • Black veil or curtain masking part of the visual field (below, above or to the side), like a shadow that spreads.
  • Sudden drop in vision or distortion of straight lines (metamorphopsia).

These four signs — flashes, a shower of floaters, a black veil, a drop in vision — can signal a retinal detachment in progress. The visual prognosis depends directly on how quickly care is provided. Do not wait until the next day.

Conversely, an old, stable phosphene (for example, an isolated peripheral flash during eye movements, known for years) with no associated sign is generally benign. A first ophthalmological opinion nonetheless remains sensible, in particular to check the state of the peripheral retina.

DIAGNOSIS

Examinations and diagnosis of phosphenes

The diagnosis rests above all on a dilated fundus examination. After a precise history covering how long the flashes have been present, their frequency, the circumstances and any associated symptoms, the ophthalmologist instils drops that dilate the pupil. This makes it possible to explore the retina right out to its periphery, where tears and areas of fragility most often lie.

The dilated fundus examination: the reference test

The ophthalmologist examines the retina using a slit lamp and a three-mirror contact lens, or an indirect ophthalmoscope with a wide-field lens. This examination makes it possible to:

  • Visualise the state of the vitreous and its attachment zone (posterior hyaloid).
  • Detect any peripheral retinal tear.
  • Identify an area of fragility (lattice degeneration) before it tears.
  • Confirm or rule out an early retinal detachment.

OCT and ultrasound as complementary tests

Optical coherence tomography (OCT) analyses the layers of the retina at high resolution. It is particularly useful for studying the macular area and detecting vitreomacular traction. Ocular ultrasound (B-mode) is valuable when the ocular media are not very transparent (intravitreal haemorrhage, dense cataract): it makes it possible to visualise the retina and the vitreous without seeing directly into them.

Management according to the findings

If the examination is normal, monitoring is arranged: the patient is reviewed at 4 to 8 weeks to check the stability of the PVD, and informed of the signs that should prompt an urgent return. If a retinal tear without detachment is found, preventive laser treatment (photocoagulation) may be proposed to “weld” it to the wall of the eye and block the passage of subretinal fluid. If a retinal detachment is already established, surgery is required (vitrectomy or scleral buckle), as an emergency for recent forms involving the macula.

Key point

The dilated fundus examination is the only test that allows the retina to be seen in its entirety. It cannot be carried out by a general practitioner. In the event of new flashes, the ophthalmologist — not the general emergency department — is the right point of contact, or a specialised ophthalmological emergency service.

FREQUENTLY ASKED QUESTIONS

Frequently asked questions about phosphenes

Phosphenes and floaters: what is the difference?

A phosphene is a brief flash of light, often located at the periphery of the visual field. Floaters are mobile shadows — filaments, grey dots — that drift across the field of view. The two can occur together during a vitreous detachment: the vitreous pulls on the retina (flash) and at the same time releases opacities that cast shadows (floaters). See also: black spots that move around.

Are phosphenes dangerous?

The great majority of phosphenes are benign. They often accompany the natural ageing of the vitreous (posterior detachment) and fade over time. Less commonly, however, they can signal a retinal tear or detachment. A sudden onset of flashes, especially with a shower of floaters or a black veil, calls for a prompt ophthalmological consultation.

Is it normal to see flashes at night?

Phosphenes are often more visible in the dark, because the contrast makes them easier to perceive. Occasional flashes in the dark, during eye movements, can be linked to benign traction of the vitreous. New, frequent or intense flashes — even at night — always warrant a fundus examination to rule out a retinal cause.

Phosphenes and migraine: how do you tell them apart?

Phosphenes of retinal origin are brief flashes, often on one side only and at the periphery of the visual field, without progression or prolonged duration. Migraine with aura instead produces shimmering luminous zigzags, broken lines or a patch that gradually enlarges, affecting both eyes and lasting 15 to 30 minutes, sometimes followed by a headache. The cerebral (not retinal) origin of migraine explains the bilateral involvement.

When should you seek urgent care for flashes of light?

You should seek urgent care in the event of a sudden onset of many flashes, especially if they are accompanied by a shower of new floaters, a black veil or curtain in the visual field, or a drop in vision. These signs may reflect a retinal tear or detachment that must be managed without delay. The visual prognosis depends on how quickly treatment is provided.

Do phosphenes disappear over time?

Often, yes. Phosphenes linked to a vitreous detachment fade over a few weeks to a few months, as the vitreous finishes detaching and the traction ceases. This natural course does not remove the need for an initial examination: only a dilated fundus examination can rule out an associated retinal tear.

High myopia and phosphenes: is there more cause for concern?

Yes, vigilance is heightened. High myopia lengthens the eyeball and stretches the retina, making it more fragile at the periphery. People with high myopia undergo PVD earlier (from 40-45 years of age) and are at higher risk of a tear. Any new phosphene in a highly short-sighted person should lead to an ophthalmological examination within 24 to 48 hours. Regular fundus follow-up is recommended, even in the absence of symptoms.

Sources

  • French Society of Ophthalmology (SFO) — Data on the vitreous, posterior vitreous detachment, retinal tears and retinal detachment.
  • College of University Ophthalmologists of France (COUF) — Item “Vitreoretinal pathology: posterior vitreous detachment, retinal tear and retinal detachment”; semiology of phosphenes.
  • French National Authority for Health (HAS) — Guidance on the management of ophthalmological emergencies and functional ocular signs.
  • Ameli.fr (French Health Insurance) — Fact sheet “Retinal detachment: symptoms, causes and treatment”.

This article is for information only and does not replace a medical consultation. Flashes of light of sudden onset, associated with a shower of floaters or a black veil, constitute an ophthalmological emergency. Only a dilated fundus examination can rule out retinal involvement and establish a personalised diagnosis.

Recent flashes of light or visual disturbance?

Dr Moïse Tourabaly, former chief clinical fellow at the Quinze-Vingts hospital, carries out a full fundus examination and directs you towards the management best suited to your situation, at consultations in Cachan or Paris 13.

Book an appointment

Related articles

Written and reviewed by Dr Moïse Tourabaly, ophthalmic refractive surgeon — former chief resident (Quinze-Vingts National Eye Hospital).

Last updated: July 5, 2026

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