Floaters Flashes and Halos

These are commonly seen. The challenge is to determine pathology (requiring ophthalmological assessment), from normal ageing (requiring reassurance).

Incidence

These are a common cause of referral to an ophthalmic emergency department and in around 25% of cases the patient has a sight threatening condition.¹

Flashes are where a person sees sudden flashes of light in the absence of a light stimulus. This may present as scintillating lights, an arc of light, or the 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.
They may be associated with an increased risk of retinal detachment, which can cause vision loss. However, other causes of flashes (and floaters) are more common than retinal detachment, such as vitreous detachment associated with ageing. Other causes include rapid eye movements (particularly in the dark) and oculodigital stimulation. Less common causes include CNS disorders (especially affecting the occipital lobe) and retinitis.
Flashes may occur on movement of the eye, such as in vitreous detachment where the vitreous is pulling on the retina and eye movement exacerbates the effect.

Migraine with aura

In this condition the flashes normally expand in a zigzag pattern across the visual field and are often accompanied by headache. They usually occur in both eyes simultaneously and disappear after a short time.
Occasionally, migrainous visual phenomena can occur in the absence of headaches (migraine sine migraine - better known as ocular migraine) but that this is a diagnosis of exclusion that can be made only after a full ophthalmological examination.

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 your 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. Usually floaters are part of the natural ageing process. Other causes of floaters include infection, inflammation (uveitis), haemorrhaging, retinal tears, and injury to the eye.

Posterior vitreous detachment (PVD)

This is separation of the posterior vitreous cortex from the inner surface of the retina. It is the underlying cause in over 60-70% cases of floaters.
Presentation: floaters and flashes of light that are more common in dim lighting. Onset can be:

• Acute - 80% cases causing floaters and flashes, occasionally with vitreous haemorrhage or retinal detachment with visual impairment or field defect. Most common form are solitary floaters but may appear as cobweb form or diffuse dots.
• Gradual - appears as intermittent floaters or may be asymptomatic.

Syneresis

When no other cause is found (approx. 25%), they are 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.
Floaters are more likely to develop with age and are more common in people who:

• Are very short-sighted - myopia
• Are diabetic
• Have had a cataract operation

Spontaneous vitreous haemorrhage

Vitreous haemorrhage accounts for approx. 5% cases of floaters.⁵ In addition to PVD, vitreous haemorrhage can occur due to retinal new vessel formation in proliferative diabetic retinopathy and retinal vein occlusion. This usually causes floaters with associated reduced vision and rarely with flashes.

Posterior Uveitis

This accounts for <1% cases of floaters. It is chronic inflammation of the uveal tract, retina and vitreous due to infectious or autoimmune disease.The floaters are caused by inflammatory infiltrates in the vitreous gel with flashes occurring occasionally in some patients. It is more frequent in young and middle-aged adults but can occur at any age.
Presentation: it is associated with a gradual blurring of vision (PVD and vitreous haemorrhage have an acute onset). Floaters may be only symptom in the early stages of posterior uveitis and should be considered as a diagnosis in any patient aged as above who presents with persistent floaters in one or both eyes.
Management: refer within next 24 hours for management by ophthalmologist. Treatment given will depend on the cause.

This is caused by light passing through water in or on the surface of the eye being broken down into its spectral colours.
Presentation: appears as rainbow-like coloured rings around lights or bright objects.
Aetiology:

• Excessive formation of tears
• Oedema of the corneal epithelium
• Glaucoma
  • Acute angle-closure glaucoma; the commonest and most clinically significant cause. It is a sight-threatening condition.
  • Chronic open-angle glaucoma
• As an early symptom of cataracts, where the glare of headlights may blind the driver so that night-time driving is impossible.
• As a late symptom of corneal endothelial dystrophy with possible impaired visual acuity.
• Pigment dispertion syndrome
• Vitreous opacities
• Drugs e.g. digitalis and chloroquine

Acute angle-closure glaucoma

This is associated with blurred vision followed by severe headache, or very severe pain in and around the affected eye. The pupil is moderately-dilated and fixed but does not respond to light, with conjunctival injection, corneal cloudiness, reduced visual acuity and occasionally nausea and vomiting.

Chronic open-angle glaucoma

Halos only occur in severe cases. It is asymptomatic in early stages with slow onset in older patients producing gradual loss of peripheral vision and cupping of the optic disc.
Management: Both forms of glaucoma should be referred for treatment by an ophthalmologist; the acute form should be discussed with the duty ophthalmologist.