Let's do a quick anatomy review before we continue: The vitreous (sometimes called vitreous humor or vitreous body) is the transparent, gel-like substance that fills the area between the lens and the light-sensitive tissue that lines the back of the eye (retina). The vitreous accounts for about 80% of the eye's volume. It is made up of water (~99% of its volume is water) and a network of proteins (collagen fibrils) and sugars (hyaluronan). As we age, the vitreous becomes less gel-like and more liquid. The vitreous is attached to the retina at a few key points.
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| From Mayo Clinic |
What we see as floaters are actually the shadows cast on the retina by substances in the vitreous. Those substances can be clumps of protein, blood cells, or pieces of tissue. Check out this great video for an illustration.
Below are a couple of Optomap images that show floaters (both photos are from the same patient- we decided she just has very photogenic floaters). Depth doesn't translate well in these photos, so here's an explanation of what we are looking at: if you cut the eyeball in half, the red tissue you see in the photos is the inside lining of the back of the eye (retina), and the strands/blobs that the arrows are pointing to are the floaters in the vitreous, which is in front of the retina.
What causes floaters?
Sometimes, floaters are no big deal. The floaters that we see from time to time are usually just that; they're clumps of fibers that cast shadows on the retina. Other times, floaters are a symptom of an eye condition.
- Posterior vitreous detachment (PVD): A PVD can occur as a result of trauma, though it's most often a result of age-related changes in the vitreous. As the vitreous shrinks and becomes more liquid, it may collapse and pull away from the retina. The point where the vitreous was attached to the optic nerve is what most people complain of- a large floater that appears somewhat suddenly. A PVD typically occurs earlier in people who are near-sighted and those who have had cataract surgery or eye trauma (1). Another symptom that may be experienced during a PVD is flashes of light. The mechanical pulling of the vitreous on the retina as it detaches can cause stimulation of the retinal photoreceptors, resulting in the perception of flashes of light. The concern with a PVD is that the pulling of the vitreous from the retina may result in a retinal break. Between 8% and 26% of acute, symptomatic PVDs are associated with a retinal tear upon initial examination. Even if no break is found upon initial examination, there is still a 2-5% chance of a retinal break being found a few weeks later (2, 3, 4). Take home point: it's impossible to know if there is cause for concern based on symptoms alone; a thorough examination is necessary.
- Retinal break: A retinal break can occur as a result of a PVD or trauma. Most retinal breaks are treated, as a break can allow fluid under the retina and cause a retinal detachment, which results in permanent vision loss if untreated.
- Vitreous hemorrhage: The vitreous contains no blood vessels, so blood in the vitreous comes from the leakage of vessels into/near the vitreous. This finding is usually associated with trauma, a PVD (with or without retinal tear, but more often with), or vascular disease. The source of the blood can be breakage of a normal retinal blood vessel, as a result of a tear or trauma, or it can be breakage of an abnormal blood vessel (neovascular membrane). For example, I had a young patient with insulin-dependent diabetes come in complaining of a cobweb in her vision. The cause of her symptoms was a large hemorrhage in the vitreous stemming from diabetic retinopathy. She had a neovascular membrane form in the back of the eye; these vessels are inherently fragile and bleed easily.
- Vitritis: A vitritis is an inflammation of the vitreous body. The inflammatory cells in the vitreous can cause floater-like symptoms. Blurred vision is also a common accompanying symptom. A vitritis can occur as a result of an infection, autoimmune disorder, or trauma, or it can be idiopathic (no known cause). This entity requires treatment.
I have floaters! What should I do?
As mentioned earlier, a few floaters every now and then is not unusual. However, you should see your eye doctor right away if you experience:
- sudden floaters and/or flashes of light
- an increase in the frequency and/or number of your floaters
- a loss of peripheral vision
How are floaters treated?
Really, they're not. The underlying cause of the floaters may need treatment, as in the case of a retinal tear, a vitreous hemorrhage, and a vitritis. PVDs, in the absence of a retinal tear, are just monitored. Floaters often become less noticeable as they break apart and settle towards the bottom of the eye, and as the brain learns to ignore them. Rarely, there are instances where laser treatment or vitrectomy (a surgery where the vitreous is removed) may be pursued to remove large, very symptomatic floaters. However, risks-vs-benefits must be carefully considered, as floaters are harmless and there are risks associated with any surgical procedures.
CliffsNotes: Occasional floaters are normal and increase with age. However, if you have sudden floaters and/or flashes of light, a loss of peripheral vision, or an increase in the frequency and/or number of your floaters, it's a good idea to go see your optometrist ASAP.
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