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F

Far Point
The point at which an object must be placed to have a sharp image on the retina of the unaccommodated eye.
Farsightedness

Hyperopia ("Farsightedness") occurs when an eye is too short for the cornea's curvature. As a result, light rays entering the eye focus behind the retina instead of precisely on the retina, and a blurred image is produced.

Example of vision with hyperopia:

human eye
Fenestration

fen-i-STRAY-shun

The drilling of tiny holes in a contact lens to allow tears to circulate more freely and to provide more oxygen to the cornea through the tear exchange.

Flare
Light streamers seen by rigid contact lens wearers whose lenses have too small an optical zone or overall diameter or whose lenses center poorly.
Flashes

As we grow older, it is common to experience flashes. Flashes of light that occur in ones vision is worth noting. Although sometimes harmless, sometimes these can also be the beginning of a serious eye problem. If the flash occurs off to side (periphery) in your vision, begin to check it out by taking your glasses off to see if it is a reflection from the edge of the frames, or the edge of the lens. If the flash is still occuring check to see if it is in both eyes or just one.

flashes

What causes flashing lights?
You may have experienced flashes if you have ever been hit in the eye and seen "stars." When the vitreous gel shrinks, it tugs on the retina which creates the sensation of flashing lights and is called a Vitreous Detachment. This may also occur after a blow to the eye and can appear randomly for several weeks or months. A sudden appearance of flashes may indicate a torn retina so to differentiate this from a vitreous detachment a visit to the optometrist or ophthalmologist is recommended.The flashes of light can appear off and on for several weeks or months. If you notice the sudden appearance of light flashes, you should visit your eye doctor immediately to see if the retina has been torn.

Sometimes the flashes are the result of a Retinal Detachment. Examination for this condition is extremely important as soon as possible.

Floaters

Floaters consist of small clumps or strands of blood cells or sloughed off tissue from the inner walls of the eye. These cells or clumps drift around in the vitreous fluid in the posterior region of the eye. When this debris floats near the back of the eye it casts a shadow on the retina. That shadow is interpreted by a person as something floating in the air out in front of them. As the particle drifts around, so does the observation noted by the individual. With time, almost everyone will have "floaters", sooner or later.

floaters example

Treatment:
Floaters can be very annoying or distracting to ones activity. As such, the question arises regarding their removal. The answer to this question lies within the magnitude of the observations. Treatment for this condition consists of literally draining the vitreous fluid from the inside of the eye, and replacing it with fresh clear fluid. This procedure is called a Vitrectomy. Obviously, this is a rather serious treatment for someone who only has a few spots that occur occasionally. However, if the individual has had an extensive hemorrhage in the eye and the vision is significantly reduced, then replacement of the vitreous is a reasonable alternative.

WARNING:
While most of the time floaters are benign, occasionably a sudden onset of new floaters can be a sign of a more serious condition such as a retinal tear, hemorrhage or detachment. Most of the time, there is no pain involved when these are happening. The back of the eye does not have any nerves that sense pain. For this reason a person having a sudden onset of floaters may delay proper care. It is highly recommended, if there is an observable change in the numbers of floaters, you should see your Eye Doctor (Optometric Physician or Ophthalmologist) to evaluate what has happened.

Fluorescein

FLOOR-ah-seen

A fluorescent dye that is instilled in the eye to evaluate the fit of rigid lenses and to highlight corneal staining, abrasions, and other corneal pathology. The pattern formed by fluoroscein stained tears flowing under a rigid lens shows the relationship between the lens and the cornea.

Additional keywords and misspellings:
fluoroscein fluoroscien floroscene contrast dye yellow fluroscine fluroscien florasein

Fluorescein Angiography

Fluorescein Angiography is a procedure used mostly to discover if blood vessels are leaking blood serum in the retina, choroid, and optic nerve. It is also used to measure the success of laser treatment on leaking blood vessels.

Fluorescein Angiography

How The Dye Works:
If the leaking holes in the blood vessels are large enough, what leaks out will be red, since it will contain red blood cells. Fluorescein Angiography is not needed to observe leakage when the holes are large enough for red blood cells to escape. However, if the holes in the vessels are smaller than the diameter of a red blood cell, then only the blood serum will leak out, leaving the red blood cells behind. Blood serum is clear, and therefore it can not be seen when looking at the back of the eye (fundus), considering how the back of the eye is covered with "wet, clear vitreous" already. With Fluorescein dye mixed with the blood serum, the blood serum can now be seen. The fluorescein dye will remain in the entire individual's blood for about 2 hours. Fluorescein is an inert vegetable dye, so the kidneys will easily remove the dye from the blood, at which time the individual will notice that their urine is discolored.

Procedure:
Fluorescein dye can be administered in two ways. It can be injected intraveniously or ingested by drinking a glass of juice containing fluorescein. After waiting only a brief period, the camera containing a blue filter, is used. As the dye begins to illuminate to its peak point, the camera is used to take pictures of the areas in question. Black and white film is used in the traditional cameras, while newer electronic digital cameras are becoming more common place. With digital cameras, the images are available immediately, while with film type cameras, there is usually a period of time needed to wait for the development of the film.

Results:
The lighter areas, on the developed film, indicate areas of leakage. The real value of Fluorescein Angiography is that with this procedure you can see where the leaking spots are even though the fluid leaking is actually clear (free of red blood cells).

Additional keywords and misspellings:
fluoroscein fluoroscien floroscene contrast dye yellow fluroscine fluroscien florasein

Fornix
The junction of the palpebral and bulbar conjunctivas.
Fovea

foh'vee-ah

A small dimple in the retina where cones are concentrated and vision is most acute.

Freckle
An increased melanin content of a cell.
Fundus

FUN-duss

The fundus is, collectively, the interior rear portion of the eye. This region includes the retina, choroid, sclera, optic disk and blood vessels. The fundus includes the central region as well as the peripheral region of the eye.

Fusion
The combining of images received by both eyes into one image.
 
The Eye Encyclopedia is a collection of eye care terminology created by practicing optometrists and ophthalmologists. The information provided is not intended to be a substitute for regular medical care or to diagnose or treat any medical condition, and should be used only as a supplemental source of information. Please consult your doctor if you have any questions or concerns about your eye health.