Flashes and floaters



Flashes and floaters are a common ophthalmic presentation.

Flashes and floaters are common presenting complaints. They can be caused by both benign and potentially sight-threatening pathologies. For this reason, most patients usually warrant a referral to ophthalmology.


Photopsia, or ‘flashes’, refer to the perception of light without an objective stimulus. They may be described as seeing ‘stars’, ‘lightening streaks’ or ‘flashing lights’. They are essentially visual hallucinations of light with geometric-like structures (e.g. triangles, diamonds).

The underlying aetiology of ‘true’ flashes is inappropriate stimulation of the optic nerve or the retina. The main mechanism is retinal traction occurring as a result of the vitreous pulling on the retina (e.g. posterior vitreous detachment, retinal detachment and diabetic retinopathy). Several neurological causes may also lead to photopsia.

There are other terms to describe the abnormal perception of light within the visual field that are not true flashes and these include:

  • Dysphotopsia: an unwanted perceived visual image that is actually an illusion
    • Glare: dazzle of light which can make it difficult to see, associated with cataracts and other media opacities
    • Haloes: perception of ring-shaped light, associated with corneal oedema and some media opacities.
  • Phosphenes: visual sensations evoked by stimulation of the visual system that is not caused by light entering the eye (e.g. rubbing the eye or eye movements)


Floaters are often described as ‘spots’, ‘squiggly lines’, ‘specks’, ‘flies’ or ‘cobwebs’, which drift in the field of vision and move with eye movements.

The vitreous is the fluid that fills the space called the vitreous chamber, between the lens and the retina. The majority of floaters are formed from small vitreous particles. Aetiology varies from benign vitreous syneresis (due to degeneration of the vitreous that has no effect on vision and usually does not require treatment) to sight-threatening pathologies such as vitreous haemorrhage and posterior vitreous detachment.

Differential diagnosis

Vitreous haemorrhage and retinal detachment are serious sight-threatening causes of flashes and floaters.

The causes of flashes depend on whether these are 'true flashes' or 'pseudo flashes'. The causes of floaters can be grouped together.

There are a few causes that can present with both flashes and floaters, which include:

  • Posterior vitreous detachment: separation of the posterior vitreous from the retina
  • Retinal tear: a tear in the lining of the retina, usually secondary to a posterior vitreous detachment. May progress to a retinal detachment
  • Retinal detachment: separation of the neurosensory retina from the underlying retinal pigment epithelium
  • Tumours: for example uveal metastasis due to melanoma

Therefore, flashes with floaters should make you think of vitreoretinal pathology.


This refers to the perception of light without an objective stimulus. In essence, something pathological is happening to the retina or optic nerve in the eye.

The main ocular causes include:

  • Posterior vitreous detachment (PVD): the posterior aspect of the vitreous separates from the retina. It is an age-related change due to degeneration and shrinkage of the vitreous. Separation may causes flashes but clinically that have normal vision, no visual field defects and no relative afferent pupillary defect. The problem is that it can lead to retinal tears and detachment.
  • Retinal detachment: the neurosensory retina separates from the retinal pigment epithelium. Most retinal detachments occur following PVD. This is because PVD causes the vitreous to pull on the retina leading to tractional retinal detachment. PVD can also cause a retinal tear leading to leakage of the vitreous between the neurosensory retina and the retinal pigment epithelium. This is known as rhegmatogenous retinal detachment. Retinal detachment classically causes acute, painless loss of vision with flashes and/or floaters.
  • Diabetic retinopathy: this is a chronic, progressive disease of the retinal microvasculature resulting from uncontrolled hyperglycaemia in diabetes mellitus. One of the major complications is tractional retinal detachment.
  • Optic neuropathy: damage to the optic nerve (e.g. papilloedema due to raised intracranial pressure or central retinal artery occlusion) can lead to flashes. However, in these conditions other ophthalmic and neurological features such as visual loss and/or headache usually precede photopsia.

NOTE: Rarer causes of true flashes include sickle cell retinopathy and retinopathy of prematurity. Both can predispose to retinal detachment.

Several neurological causes can result in photopsia by different mechanisms. These include:

  • Migraine: flashes can occur in both migraine with visual aura and ocular migraine (visual symptoms without headache). An estimated 15-20% of patients with migraine have an aura and >90% of these are visual.
  • Occipital lobe pathology: this may include tumours, arteriovenous malformations, epilepsy or even stroke. These pathologies can cause coloured shapes to appear in vision and there may be associated visual changes (e.g. visual field loss).
  • Charles Bonnet syndrome: this refers to the experience of visual hallucinations in patients with severe loss of vision.
  • Medications: some drugs in overdose or given at high doses can lead to photopsia (e.g. digoxin, voriconazole, quetiapine).


Floaters are essentially 'dark spots' or 'squiggly lines' within the visual field due to abnormalities within the vitreous. Broadly, floaters may be caused by debris in the vitreous secondary to infection, inflammation, haemorrhage, or degeneration. The major causes of floaters include:

  • Posterior vitreous detachment: in PVD small opacities develop in the vitreous that become mobile leading to the appearance of floaters
  • Vitreous haemorrhage: bleeding into the vitreous can cause sudden onset of floaters and loss of vision. The larger the bleed, the great the impact on vision. Visual loss is typically painless and causes include trauma, retinal tear/detachment and friable vessels from neovascularisation.
  • Vitritis: this refers to inflammation of the vitreous body. Chronic inflammation causes debris. May be infectious or non-infectious.
  • Asteroid hyalosis: a common, usually benign condition where calcium-lipid complexes are suspended through the vitreous. It has been associated with ageing.
  • Ocular amyloidosis: due to deposition of amyloid in the vitreous
  • Vitreous syneresis: a benign condition depicting degeneration of the vitreous. Risk factors include myopia, older age, diabetes, following cataract surgery.


The history is particularly important to determine the acuity of symptoms and the impact on sight.

There are some really important questions to ask in the clinical history to help determine the cause of both flashes and floaters.

History of presenting complaint

For floaters, enquire about what they look like, how many there are, and whether they are unilateral or bilateral. Bilateral photopsia is suggestive of a central nervous system cause or a systemic illness. Floaters may be the first indication of a retinal tear or detachment. Alternatively, they could be long-standing and chronic related to vitreous syneresis.

For flashes, it is important to ask the patient to describe them. Are these temporal flashes that can be associated with PVD, retinal tear, or retinal detachment? Alternatively, are these shimmering lights with a scotoma that is associated with migraine or occipital lobe pathology? Also, think about how long they last and when they are noticed.

The acuity of visual symptoms can help determine the cause:

  • Acute onset: vitreous haemorrhage, PVD, retinal detachment
  • Gradual onset: diabetic retinopathy, papilloedema, vitreous syneresis, asteroid hyalosis, amyloidosis, ocular migraine

Visual loss

The presence and extent of visual loss are essential questions for any ophthalmic presentation. Visual changes in PVD are typically absent or very mild but if this progresses to retinal detachment there can be a sudden loss of vision. This is sometimes described by patients as a 'curtain of darkness'. A vitreous haemorrhage can cause significant vision loss, but this depends on the extent of the bleed. Visual changes that occur in migraine are typically transient.

Some of the major risk factors for developing retinal detachment that can lead to sudden, painless loss of vision include:

  • Myopia (i.e. short-sightedness)
  • Trauma (leads to retinal tears)
  • Cataract surgery
  • Previous retinal detachment surgery
  • Advancing age
  • Family history (e.g. retinal tear, break or detachment)
  • Proliferative diabetic retinopathy
  • Many others

Past medical history

Conditions such as diabetes mellitus and migraine with aura increase the likelihood of patients developing flashes and floaters. Major causes of uveitis can also predispose to flashes and floaters including infection, ocular injury and inflammatory diseases (e.g. sarcoidosis, ankylosing spondylitis). In addition, determine any previous ocular or intracranial surgery and history of cancer (e.g. melanoma may present with uveal metastasis).

Drug history

Medications can affect the eyes in many different ways. Some commonly implicated medications that may cause flashes and floaters include:

  • Chloroquine (anti-malarial)
  • Diphenhydramine (anti-histamine)
  • Digoxin
  • Quetiapine
  • Voriconazole

Social history

Retinal vascular disease can occur with drugs of abuse such as cocaine, so it is important to broach this subject sensitively. It is imperative that you determine the patients occupation and driving status as the extent of visual symptoms including visual loss may have an impact on their work and ability to drive.


Formal slit lamp examination enables the identification of the major ocular pathologies associated with flashes and floaters.

Basic examination findings in any clinic can include an assessment of visual acuity using a Snellen chart, assessment of the visual fields, and ophthalmoscopy to assess the retina. In patients with a significant retinal pathology (e.g. large detachment), there may be a relevant afferent pupillary defect (RAPD) that can be determined through the 'swinging light test'. This test essentially assesses the difference between how each pupil responds to light and depends on the functioning of the retina and optic nerve.

Any patient presenting with sudden onset of flashes and floaters and with no other signs of retinal detachment should be seen within 24 hours by a practitioner who can complete a slit lamp examination and indirect ophthalmoscopy.

Immediate referral

An immediate referral to an ophthalmologist for same-day assessment is warranted for a dilated fundal exam and further management in any case of new flashes/floaters alongside:

  • Visual field loss
  • Blurred or distorted vision
  • Loss of visual acuity
  • Retinal detachment or vitreous haemorrhage on fundoscopy

NOTE: Longstanding symptoms of flashes and floaters can be referred for a non-urgent ophthalmology review.


Highly specialised investigations may be used but this largely depends on the suspected cause.

The choice of further investigations depends on the suspected cause, severity, and need for any interventions. For example, the investigation of a suspected occipital lobe pathology will vary greatly from a suspected retinal pathology.

Two important ophthalmic tools that may be utilised for suspected ocular causes include:

  • Optical coherence tomography (OCT): This is a noninvasive imaging technique that uses light waves to take a cross-sectional image of the layers of the retina
  • Ocular ultrasound: a quick, and readily available bedside tool that can be used to assess patients with acute vision loss, ocular trauma, headache, or concern for increased intracranial pressure.

Key tip

Acute onset flashes or floaters and visual field loss need same-day referral to an ophthalmologist.

Due to the potential of flashes and floaters to represent sight-threatening pathology, ensure the history and examination are orientated to screening for these pathologies and have a low threshold for urgent referral to ophthalmology if suspected. The importance of an urgent ophthalmology review in these situations is to perform a thorough ophthalmic examination and exclude severe vitreoretinal pathologies (e.g. detachment, vitreous haemorrhage).

Last updated: August 2022
Author Dr Monisha Edirisooriya Monisha is an FY2 working in the South Thames deanery. She is interested in pursuing a career in ophthalmology. Her other interests lie in widening participation in medicine and medical education.

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