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- farsightedness (hyperopia)
- Vision that results when the distance from the cornea to the retina is too short.
This occurs when the eye that has a vertical oval shape, or it has a cornea that is
flatter than normal. In either event, a person who is farsighted sees well at a
distance but has poor reading vision. Those who are farsighted are usually born
with the disorder.
- FDA
- Acronym for the Food and Drug Administration. It is a United States government
agency responsible for the evaluation and approval of medical devices, including
contact lenses, intraocular lenses and Excimer lasers. In the U.S., the FDA must
approve these products before they can be marketed. Contrary to popular belief,
the FDA does not evaluate surgical procedures unless they require a new medical
device.
- field analyzer
- Automated projection perimeter instrument which uses projected points of light to
determine central or peripheral field of vision. Used for early diagnosis, treatment and
management of diseases resulting in visual field loss.
See Free Eye Tests.
- fixation
- The act or an instance of focusing the eyes on an object.
- fixation point
- The point in the visual field on which the two eyes focus in normal vision, and for each eye is the point that directly stimulates the fovea of the retina.
- flashers
- Bright bursts of light that are sometimes seen when the eyes are closed. These
occur normally as the eye ages and the vitreous humor, which is jelly-like
substance that fills center cavity of eye, begins pulling away from the retina. The
flashes can appear off and on for several weeks or months. If there is a sudden
appearance of many light flashes, an ophthalmologist should be consulted
immediately to see if the retina has been torn.
- flicker
- The wavering or fluttering visual sensation produced by intermittent light.
- floaters
- Particles that float in the vitreous, which is jelly-like substance that fills center cavity of
eye, and cast shadows on the retina. The particles appear to be strung together with a
web-like thread. Some floaters are formed before birth while others occur normally with
aging. The sudden appearance of many floaters can be an indication of a serious eye
disorder and should be checked by an eye care professional.
See Free Eye Tests.
- fluorescein angiography
- Test used to examine blood vessels in the retina, choroid and iris of the eye. Fluorescein
dye is injected into an arm vein and rapid, sequential photographs are taken of the eye as
the dye circulates.
- focal length
- The distance of a focus from the surface of a lens or concave mirror. Relates to the distance between an image source and a lens and the distance of the lens to the image.
- Food and Drug Administration
- The Food and Drug Administration is a United States government agency responsible for
the evaluation and approval of medical devices, including contact lenses, intraocular lenses
and excimer lasers. In the U.S., these products must be approved by the FDA before they
can be marketed. Contrary to popular belief, the FDA does not evaluate surgical
procedures unless they require a new medical device.
- fovea
- A small rodless area of the retina that affords the sharpest vision because the layers of the retina spread aside to let light fall directly on the cones, which are the cells that give the clearest vision.
- frequent replacement contact lenses
- Contact lenses replaced on a planned schedule, usually every 2 weeks, monthly or
quarterly. Can be daily or extended wear lenses.
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