Q: Over the years, I occasionally experience a streak of light across my vision, which goes away quickly. However, I have recently noticed a persistent small black spot when looking out of my right eye. Otherwise, my vision seems fine. Do I need to worry?

A: What you describe sounds like flashes and floaters. Both commonly happen as we get older.

The eye consists of two major compartments — the front (including the cornea, iris, and lens) and the back (the rear two-thirds of the eyeball, including the retina and a large cavity filled with vitreous gel that attaches to the retina).

Flashes, the quick streaks of light you describe, tend to be most noticeable in the dark. They occur when the vitreous gel bumps, rubs, or tugs against the retina. This action can lead to small areas of vitreous detachment, a sudden separation between the vitreous gel and the retina.

The small black spot you see in one eye sounds like a typical floater. People often notice occasional floaters — spots, squiggly lines, rings, or opaque flecks — drifting across their line of vision. Floaters are tiny clusters of cells or clumps of gel that have formed in the vitreous cavity. What the person sees is the shadow that these little clumps cast on the retina.

People often become more aware of floaters when they look at a book page, a computer screen, or a solid, light-colored background. Floaters can also be more noticeable when you’re tired.

Unlike flashes, floaters don’t disappear. However, over time, they become much less noticeable for several reasons. The brain eventually filters out unimportant or repetitive information, including floaters. The clumps of gel can also shift position and move away from your central vision.

Occasional flashes and one or two small floaters are generally harmless. However, certain features may signal a retinal detachment, a potentially serious problem where the retina tears away from the back of the eye. Immediately call for medical advice if you experience any of the following:

(Howard E. LeWine, M.D., is chief medical editor and an Editorial Advisory Board member at Harvard Health Publishing.)

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