Merck Manual

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Some Causes and Features of Eye Flashes and Floaters

Some Causes and Features of Eye Flashes and Floaters


Common Features*

Diagnostic Approach†

Eye disorders that are not worrisome

Vitreous contraction floaters (floaters due to shrinking of the jellylike substance that fills the back part of the eyeball, called the vitreous humor)

A few small, translucent clumps or strands that

  • Occasionally come into the field of vision

  • Move as the eye moves

  • May be more noticeable under certain lighting (such as bright sunlight)

  • May occur in both eyes, although not at the same time

No recent change in the number or type of floaters

No effect on vision

Examination by an ophthalmologist

Detachment of the vitreous humor from the retina

A sudden increase in floaters, usually in older people

Floaters that resemble cobwebs

One large floater that moves in and out of the field of vision

Photopsias that come and go

Examination by an ophthalmologist

Eye disorders that are serious

Simple, sudden flashes of light that can look like lightning, spots, or stars (photopsias), that occur repeatedly or continuously

Loss of vision that affects one area, usually what is seen out of the corners of the eye (peripheral vision)

Loss of vision that spreads across the field of vision like a curtain

Sometimes in people with risk factors for detachment of the retina (such as a recent eye injury, eye surgery, or severe nearsightedness)

Examination by an ophthalmologist

A tear in the retina


Sometimes symptoms only in the peripheral field of vision

Examination by an ophthalmologist

Vitreous hemorrhage (bleeding into the vitreous humor)

In people who have risk factors for this disorder (such as diabetes, a tear in the retina, sickle cell disease, or an eye injury)

Usually loss of the entire field of vision (not in just one or more spots)

Examination by a doctor and generally an ophthalmologist

Sometimes, ultrasonography of the retina

Inflammation of the vitreous humor (as may occur when Toxoplasma parasites, fungi, or rarely cytomegalovirus infect the eye or caused by autoimmune disorders)


Loss of vision affecting the entire field of vision

Possibly affecting both eyes

In people with risk factors for these infections (such as AIDS, injection drug use, and other conditions that weaken the immune system)

Examination by an ophthalmologist

Sometimes, testing to detect microorganisms suspected of causing infection

Disorders not related to the eyes

Ocular migraine (migraines that cause vision symptoms)

Jagged lines that appear first in the center of the field of vision, then spread outward, and disappear after about 20 minutes

Sometimes blurring of central vision

Sometimes a headache after the disturbances in vision

Sometimes in people known to have migraines

A doctor's examination alone

* Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present. Features occur in only one eye unless otherwise specified.

† Although a doctor's examination is always done, it is mentioned in this column only if the diagnosis can sometimes be made only by the doctor's examination alone, without any testing. If an ophthalmologist's examination is specifically required, that is mentioned separately.