Flashes and Floaters

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Several times each week patients call our Optometry clinics with symptoms of new floaters in their vision and/or flashes of light. The sudden onset of these symptoms can be concerning and for good reason – they can signal something very serious like a retinal tear or detachment. More commonly, they signify an aging change in the vitreous of the eye called a posterior vitreous detachment (PVD). If you or someone you know experiences new flashing lights or floaters you should see your Optometrist or other eye care professional right away. We always try to fit any patients with these symptoms into our schedules as emergencies the day they call. So what’s the big deal about these visual phenomena and what can cause them?

It is important to first differentiate flashes and floaters from other visual symptoms as the causes can be quite different. Perceived flashes of light are called photopsias and can last seconds or longer. The flashes in the case of a PVD are brief, momentary experiences of light that are often seen off to one side and are usually most noticed in dark environments. Some people describe them as lightning flashes. Flashes of light can also be from a migraine aura, in which case the duration is usually around 20-30 minutes, the flashes may be large areas of wavy colored lines and are sometimes followed by a headache. Migraine auras are more likely in patients under the age of 40 and often occur in both eyes off to the same side. These symptoms in older patients without a past history of migraine are more concerning since they can actually be warning signs for strokes.

Floaters are small dots, wavy strings or cobweb-shaped shadows that float around in your vision. They will often move out of the way when you try to look at them. These should not be confused with a blind spot, which is a fixed area of blurry or missing vision that does not move around with eye movements but rather always stays in the same location relative to your direction of gaze. Floaters are the main focus of this article but just be aware that a new transient or permanent blind spot in the field of vision should also prompt immediate investigation. Blind spots can be from problems with the retina or could potentially be something like an infarction in the brain or retina or a transient ischemic attack.  

The retina is the thin, light sensitive layer of tissue lining the inside of the eye. Next to the retina, making up the main bulk of the eye, is the vitreous. The vitreous is a gel-like substance that maintains the round shape of the eyeball. The vitreous has many fine fibers that connect it to the retina at various locations. As the eye gets older, changes take place and the vitreous becomes more liquefied in some areas and it eventually shrinks and pulls away from the retina. This pulling away is known as a posterior vitreous detachment (PVD). PVDs are most common in individuals over the age of 50 years and become even more likely with increasing age. PVDs can occur in people of any age especially if there has been head or eye trauma or in those who are nearsighted. 

There is usually a sudden increase in new floaters noticed when a PVD first occurs because some of the fine fibers that connected the vitreous to the retina are now suspended and floating in front of the retina causing shadows. The flashes often seen while a PVD is first occurring are due to pulling of the vitreal attachments on the retina which the brain interprets as flashes of light. 

A PVD in itself is not a harmful condition and requires no treatment. The new floaters often break down or become less noticeable with time. However, there are some cases where the shrinking of the vitreous away from the retina actually pulls away a piece of retina. If this occurs it is usually in the far edges of the retina and can be either a hole, tear or break in the retina. The retina may continue to tear and this can lead to a retinal detachment which can cause blindness if not treated promptly. Acute retinal tears and detachments are emergencies and must be assessed and treated by a retinal specialist within a few hours to a few days for the best visual outcomes. Occasionally, a PVD can cause a hole in the macula, the part of the retina responsible for central vision. This can present as distortion or a blind spot near the centre of vision and should be assessed by a retinal specialist. 

If you experience new floaters, flashing lights or a curtain in your vision you should see your eye care professional right away. They will most likely put dilation drops in your eyes (you will need to bring a driver with you to the appointment) to get a wide internal view of your eye. Your eye doctor will be able to fully assess your eye health to determine if you have had a simple PVD or a retinal tear, or if there is another cause for your symptoms. After your thorough eye exam your Optometrist will explain the diagnosis and make any necessary referrals to specialists if there is a retinal tear or detachment. After a PVD first occurs you should carefully monitor for another sudden increase in floaters, more flashing lights or a curtain in any part of your vision that could mean a new retinal tear or detachment. If any of these things happen you should get in to see your Optometrist again right away. It is always better to be safe than sorry – you only have two eyes!

Written by Cowichan

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