Flashes and Floaters

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.

Causes of flashes

Retinal traction

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 Tears / Retinal Detachment etc
  • Proliferative diabetic retinopathy.


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 – This is the most common cause of floaters.These are normal degenerative changes associated with age, resulting in translucent opacities.
  • Posterior vitreous detachment (may also occur with flashes).
  • Vitreous abnormalities like bleeding etc also can cause floaters.

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 nighttime driving impossible).
  • Pigment dispersion syndrome.
  • Vitreous opacities.
  • Drugs (eg, digitalis and chloroquine).
  • When to suspect a retinal detachment[6]
  • New onset of floaters (mobile dots, lines, or haze).
  • New onset of flashes (light often seen as recurrent, brief flashes).
  • Sudden painless visual field loss.
  • Reduction in visual acuity, blurred or distorted vision.

Insight Eye Clinic

155, Geetanjali Building, Sir Bhalachandra Road, Dadar East, Mumbai, Maharashtra 400014