Why do I sometimes see black spots in my vision?

"Eye floaters are spots in your vision. They may look to you like black or gray specks, strings, or cobwebs that drift about when you move your eyes and appear to dart away when you try to look at them directly.

Most eye floaters are caused by age-related changes that occur as the jelly-like substance (vitreous) inside your eyes becomes more liquid. Microscopic fibers within the vitreous tend to clump and can cast tiny shadows on your retina. The shadows you see are called floaters.

If you notice a sudden increase in eye floaters, contact an eye specialist immediately — especially if you also see light flashes or lose your peripheral vision. These can be symptoms of an emergency that requires prompt attention."

"Symptoms
Symptoms of eye floaters may include:

Small shapes in your vision that appear as dark specks or knobby, transparent strings of floating material
Spots that move when you move your eyes, so when you try to look at them, they move quickly out of your visual field
Spots that are most noticeable when you look at a plain bright background, such as a blue sky or a white wall
Small shapes or strings that eventually settle down and drift out of the line of vision
When to see a doctor
Contact an eye specialist immediately if you notice:

Many more eye floaters than usual
A sudden onset of new floaters
Flashes of light in the same eye as the floaters
Darkness on any side or sides of your vision (peripheral vision loss)
These painless symptoms could be caused by a retinal tear, with or without a retinal detachment — a sight-threatening condition that requires immediate attention."

"Eye floaters may be caused by the normal aging process or as a result from other diseases or conditions:

Age-related eye changes. As you age, the vitreous, or jelly-like substance filling your eyeballs and helping them to maintain their round shape, changes. Over time, the vitreous partially liquefies — a process that causes it to pull away from the eyeball's interior surface. As the vitreous shrinks and sags, it clumps and gets stringy. This debris blocks some of the light passing through the eye, casting tiny shadows on your retina that are seen as floaters.
Inflammation in the back of the eye. Posterior uveitis is inflammation in the layers of the uvea in the back of the eye. This condition can cause the release of inflammatory debris into the vitreous that are seen as floaters. Posterior uveitis may be caused by infection, inflammatory diseases or other causes.
Bleeding in the eye. Bleeding into the vitreous can have many causes, including diabetes, hypertension, blocked blood vessels and injury. Blood cells are seen as floaters.
Torn retina. Retinal tears can occur when a sagging vitreous tugs on the retina with enough force to tear it. Without treatment, a retinal tear may lead to retinal detachment — an accumulation of fluid behind the retina that causes it to separate from the back of your eye. Untreated retinal detachment can cause permanent vision loss.
Eye surgeries and eye medications. Certain medications that are injected into the vitreous can cause air bubbles to form. These bubbles are seen as shadows until your eye absorbs them. Certain vitreoretinal surgeries add silicone oil bubbles into the vitreous that can also be seen as floaters."

Source: Mayo Clinic

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