eyes, spots in front of the The spontaneous appearance of spots in the eyes. Also known as “floaters,” spots are usually images formed by deposits of protein drifting about in the vitreous humor (the clear, jelly-like substance that fills the middle of the eye). The appearance of permanent or recurring white or black spots in…
eyes, flashing lights in the Spontaneous flashing-light sensations in the eyes that can be caused by a number of factors. A sensation of flashing lights can be caused when the vitreous humor (the clear, jelly-like substance that fills the middle of the eye) shrinks and tugs on the retina. These flashes of light can appear…
eyelids, congenital ptosis of the Drooping of the upper eyelids at birth. Moderate or severe ptosis calls for surgical treatment to permit normal vision development. If moderate or severe ptosis is not corrected, amblyopia (“lazy eye”) may develop, which can lead to permanently poor vision. Congenital ptosis is often caused by poor development of the…
eyelids, adult ptosis of the Drooping of the upper eyelids in adults, most commonly due to separation of the tendon of the lid-lifting (levator) muscle from the eyelid. This may occur with age, after cataract or other eye surgery, or due to an injury, an eye tumor, or a complication of another disease that involves…
eyelid The lid or cover of the eye, a movable fold of skin and muscle that can be closed over the eyeball or opened at will. Each eye has an upper and a lower lid. Also known as a palpebra.
eyedrop test A test that involves putting certain liquids into the eye to produce a particular response. There are many types of eyedrops and many types of eyedrop tests. One of the most common eyedrop tests is pupil dilation. See also dilation, pupil.
eye chart test A test that measures vision ability at various distances. An eye chart is imprinted with block letters that line-by-line decrease in size, corresponding to the distance at which each line of letters is normally visible. See also chart, Snellen.
eye The organ of sight. The eye has a number of components, including the cornea, iris, pupil, lens, retina, macula, optic nerve, and vitreous humor. The cornea is the clear front window of the eye that transmits and focuses light into the eye. The iris is the colored part of the eye, and regulates the…
extremity An uttermost part of the body, such as a hand or a foot.
extrauterine pregnancy See ectopic pregnancy.
extrasystole A premature contraction of the heart that is independent of the normal rhythm of the heart. An extrasystole begins in a part of the heart other than the normal heartbeat origin, the sinoatrial (SA) node. Extrasystoles are followed by a pause, as the heart electrical system “resets” itself, and the contraction following the pause…
extrapyramidal system The part of the nervous system that regulates muscle reflexes.