There are a number of different types and causes of "floaters". The most common type are those annoying little black specks which seem to dart away---just out of sight--as you look for them. Often these are small remnants of embryonic blood vesse ls, flecks of pigment floating freely in the aqueous fluid in the front of the eye or strands in the more jelly-like vitreous in the back of the eye. (The vitreous fills nearly the entire inside of the eye ball. ) Floaters are also caused by small pigment flecks deposited on strands of muscle fibers attached to the iris.
Floaters can be due to variations in refractive index (optical density) in the vitreous inside the eye resulting in shadows being cast on the retina. Imagine fiberglass strands submerged in water and illuminated by a flashlight. Although both the water an d the strands are clear they have different optical characteristics, and the strands will cast a shadow.
Small translucent strand-like floaters can be the viewer's perception of mucous strands floating in the pre-corneal tear layer. Tears are made of a mixture of oil, water and mucous and at times the three elements separate, forming floating globules o f oil or mucous. And under the right conditions, you may "see" shadows of individual blood cells darting through the blood vessels in the back of the eye.
All of these types of floaters are quite benign. They are harmless. It is common for floaters to appear suddenly and diminish in their appearance over time. The exceptions to these conditions are often signs of potential serious pathology.
The serious floater: Occasionally floaters are warning signs of imminent danger or damage occurring somewhere in the eye. An internal hemorrhage of blood from a leaking vessel may cause floaters. They can also be caused by a Posterior Vitreous Detachmen t (PVD), a degenerative change in the vitreous allowing it to fall away from its normal position against the retina. This usually causes an acute increase in the number of floaters and is associated with increased risk of retinal complications. This is ra re in the under 50 crowd, with the incidence becoming more common by age 70 or so. The rapid onset of large and numerous floaters may signal an impending retinal detachment.
The floaters which indicate a serious condition usually can be differentiated by some important factors: 1: they occur suddenly, 2: are accompanied by visual field defects including flashes of light and areas of vision loss (as if a dark curtain is place d in front of the eyes), 3: appear numerous or large, 4: are associated with a trauma or a blow to the eyes or head. It often appears as if they are increasing, not decreasing in numbers (and annoyance) over a short period of time, often minutes or hours .
These signs and symptoms are considered ocular emergencies and require immediate medical attention.
Flashes of light: These apparent bursts of light can be small, bright pin-point objects, sparkles, zig-zag patterns or even appear like a lightning storm. The phenomena has one root cause: non-optical stimulation of the retinal photoreceptors.
This event may occur from traction on the retina from PVD (see above) or a loss of blood supply to the neurological tissue, such as in transient ischemia or retinal detachment. Transient ischemia is the blockage of an artery (actually arteriole, a smaller b ranch vessel) supplying a part of the retina. The blockage can occur as a result of a clot or embolus lodged in the vessel. It also may be caused by a spasmodic constriction of a small vessel similar to what occurs during migraine.
The difference between ophthalmic migraine and the more serious embolism event and retinal detachment is that the visual disturbances associated with migraine transient ischemia always resolve within a few minutes, and almost never more than about twenty minutes (rare ly up to 40 minutes). There can be visual field disturbances such as zig-zag, shimmering or wavering images. It is often, but not always followed by the typical migraine headache and nausea. On the other hand, the visual field effects caused by embolisms and retinal detachment related flashes don't stop and often become increasingly more noticeable with time. The visual field disturbances are more clearly areas of gray or dark blind spots.
Any flashing light or visual disturbance that lasts more than twenty to forty minutes is considered an ocular emergency and requires immediate medical attention.
It is always wise to consult with an eye doctor when visual disturbances indicate a potentially serious problem. Very often these are warning signs which relate to not only eye problems, but other systemic pathology and disease. These include: hypertensio
n (high blood pressure), arteriosclerosis ("hardening of the
arteries"), sickle cell disease, impending heart attack or stroke,
and other serious conditions. Examination by an optometrist or ophthalmologist may determine if further referral or trea
tment is indicated. Intervention and treatment can help prevent permanent and significant damage.