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Floaters are a common complaint, as are flashes to a lesser extent. The two may occur separately or together, depending on the underlying pathology. Haloes are less common. Flashes and floaters are a common complaint in primary care. Most patients have a harmless collapse of the vitreous gel (posterior vitreous detachment). However, some may have a more a serious underlying cause, such as a retinal detachment.
It is very difficult, without the help of a slit lamp, to determine whether they arise out of the more common, benign causes or whether they are due to one of the less common, sinister causes.
There are some suggestive pointers which will be outlined here which will guide the urgency of the referral; ultimately, most patients will need an ophthalmological review.
Otherwise known as 'photopsia', flashes describe the subjective sensation of seeing a light in the absence of an objective stimulus. This may present as scintillating lights, an arc of light or a feeling like a light-bulb has just flashed on and off in the periphery of vision. Flashes are caused by improper stimulation of the eye's retina, or the optic nerve, which the brain interprets as light. This could be traction of the retina, for example.
Aetiology of flashes
The vitreous is the viscous filling occupying most of the globe. It is loosely attached, at its periphery, to the retina. In some parts, it is more firmly adherent. Any condition which causes it to contract (eg, fibrosis as a primary problem or following haemorrhage, the natural progressive liquefaction that occurs with age) has the potential to result in flashes, as the vitreous pulls on the retina in the process. These conditions include:
- Vitreous detachment (may also occur with floaters).
- Retinal detachment.
- Diabetic retinopathy.
- Retinopathy of prematurity.
Central nervous system pathology
- Papilloedema - symptoms tend to be transient, associated with straining or change in posture.
- Migraine - classically: gradually enlarging, frequently bilateral, zigzag fortification spectra usually followed by a headache. Occasionally, migrainous visual phenomena can occur in the absence of headaches (migraine sine migraine - better known as ocular migraine) but this is a diagnosis of exclusion that can be made only after a full ophthalmological examination.
- Occipital lobe lesions (eg, tumours or arteriovenous malformations) - tend to cause coloured shapes and blobs.
- Charles Bonnet syndrome - complex visual hallucinations brought about by bilateral, severe visual loss.
Although not strictly speaking flashes, the following may be described as such by the patient:
- Photophobia - usually associated with anterior segment inflammation or retinal hypersensitivity.
- Glare - a dazzle usually associated with media opacities.
- Haloes - the ring effect associated with media clouding (eg, the corneal oedema of acute angle-closure glaucoma) and occasionally, media opacities.
Floaters are opacities floating in the field of vision, which may be seen as spots, thread-like strands or squiggly lines. They are variously described by patients as 'specks', 'flies', 'spiders' and if extensive, 'like a cobweb'. They move with eye movements and seem to dart away when you try to look at them directly. They do not follow eye movements closely, and usually drift when the eyes stop moving. There are a number of causes of floaters:
- Vitreous condensations - these are normal degenerative changes associated with age, resulting in translucent opacities.
- Posterior vitreous detachment (may also occur with flashes).
- Vitreous haemorrhage (eg, proliferative diabetic retinopathy or retinal vein occlusion) - minor bleeds are seen as 'spots' in the vision (the fundus is easily visualised); major bleeds result in a severe decrease in the visual acuity (fundus is poorly visualised).
- Vitritis - inflammatory cells in the vitreous due to intermediate or posterior uveitis.
- Asteroid hyalosis - a (usually benign) condition characterised by small yellow/white particles scattered throughout the vitreous.
- Amyloidosis - sheet-like opacities.
- Tumours (eg, lymphoma) - floaters occur as a result of vitritis.
When no other cause is found (approximately 25% of cases), floaters may be due to degeneration of the vitreous, where collagen fibres become thickened with vitreous liquefaction, and hence visible. These are not associated with flashes, reduced vision or defects in the visual field. They are usually of gradual onset. Patients should be reassured that these are a normal feature and require no treatment unless the situation deteriorates. They tend to 'settle' at the bottom of the eye, below the line of sight, where they are less distracting. Most people learn to ignore them. Floaters can become apparent when looking at something bright, such as white paper or a blue sky. They are more likely to develop with age and are more common in people who:
Flashes with floaters
These tend to occur with:
- Posterior vitreous detachment
- Retinal tear
- Retinal detachment
These are caused by light passing through water in or on the surface of the eye, being broken down into its spectral colours. This results in rainbow-like coloured rings around lights or bright objects. Acute angle-closure glaucoma is the most common and the most clinically significant cause. It is a sight-threatening condition. However, there are a number of other causes:
- Excessive formation of tears.
- Oedema of the corneal epithelium from any cause (eg, contact lens overwear).
- Corneal dystrophies in their later stages.
- Chronic open-angle glaucoma.
- Early cataracts (glare of headlights making night-time driving impossible).
- Pigment dispersion syndrome.
- Vitreous opacities.
- Drugs (eg, digitalis and chloroquine).
When to suspect a retinal detachment
- New onset of floaters (mobile dots, lines, or haze).
- New PINK floater (being almost always associated with a retinal tear and small bleed).
- New onset of flashes (light often seen as recurrent, brief flashes).
- Sudden painless visual field loss.
- Reduction in visual acuity, blurred or distorted vision.
- A relative afferent pupillary defect if there is extensive detachment (see the separate Examination of the Eye article).
- Fundoscopy: loss of the red reflex, vitreous opacities, or detached retinal folds (appear pale, opaque and wrinkled).
- Infants usually present with a white pupillary reflex (leukocoria) or squint (strabismus).
- In older children, most retinal detachment is secondary to trauma.
Further reading and references
; A Welsh Eye Care Initiative Guideline, NHS Wales
; College of Optometrists, 2019
; Flashes, floaters, and a field defect. BMJ. 2013 Nov 4347:f6496. doi: 10.1136/bmj.f6496.
; NICE CKS, March 2015 (UK access only)
; Royal College of Ophthalmologists (Dec 2012)
; Retinopathy of prematurity. Lancet. 2013 Oct 26382(9902):1445-57. doi: 10.1016/S0140-6736(13)60178-6. Epub 2013 Jun 17.
; AAO Retina/Vitreous PPP Panel, Hoskins Center for Quality Eye Care, October 2014
; Vitreous Floaters
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