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Eyes and Vision Glossary

Terms used to explain Eyes and Vision can sometimes be confusing. To help you fully understand the articles and features related to this very important health topic, we have compiled a glossary of terms that can help.

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Pronunciation: \-ˈjen-ə-səs\

Function: noun
pl -e*ses
Pronunciation: \-ˌsēz\
: the formation and differentiation of blood vessels


Function: noun
: any of various usu. yellow to red pigments (as carotenes) found widely in plants and animals and characterized chemically by a long aliphatic polyene chain composed of eight isoprene units


Pronunciation: \ˈkat-ə-ˌrakt\

Function: noun
: a clouding of the lens of the eye or its surrounding transparent membrane that obstructs the passage of light


Pronunciation: \ˈkōn\

Function: noun

1: a solid having a circular base and sides that slope evenly to a point
2 a: any of the conical photosensitive receptor cells of the vertebrate retina that function in color vision compare rod
b: any of a family (Conidae) of numerous somewhat conical tropical gastropod mollusks that include a few highly poisonous forms see conus
3: a cusp of a tooth esp. in the upper jaw


Pronunciation: \ˈkor-nē-ə\

Function: noun
: the transparent part of the coat of the eyeball that covers the iris and pupil and admits light to the interior


Pronunciation: \dī-ˈlāt, ˈdī-ˌ\

Function: verb
transitive verb: to enlarge, stretch, or cause to expand <dilate his pupils with atropine> <the drug dilates peripheral arteries> intransitive verb: to become expanded or swollen <the cervix was dilating> <the pupils dilated>


Pronunciation: \ˈfō-vē-ə\

Function: noun
pl fo*ve*ae
Pronunciation: \-vē-ˌē, -vē-ˌī\

1: a small fossa
2: a small rodless area of the retina that affords acute vision


Pronunciation: \glau-ˈkō-mə, glo-\

Function: noun
: a disease of the eye marked by increased pressure within the eyeball that can result in damage to the optic disk and gradual loss of vision


Pronunciation: \ˌin-trə-ˈäk-yə-lər, -(ˌ)trä-\

Function: adjective
: implanted in, occurring within, or administered by entering the eyeball <intraocular injections> <intraocular lens implantation>


Pronunciation: \ˈlā-sik\

Function: noun
: a surgical operation to reshape the cornea for correction of nearsightedness, farsightedness, or astigmatism that involves the use of a microkeratome to separate the surface layer of the cornea creating a hinged flap providing access to the inner cornea where varying degrees of tissue are removed by an excimer laser followed by replacement of the corneal flap —called also laser-assisted in-situ keratomileusis


Pronunciation: \ˈlā-zər\

Function: noun
: a device that utilizes the natural oscillations of atoms or molecules between energy levels for generating coherent electromagnetic radiation usu. in the ultraviolet, visible, or infrared regions of the spectrum

Low Vision

low vision
Function: noun
: impaired vision in which there is a significant reduction in visual function that cannot be corrected by conventional glasses but which may be improved with special aids or devices


Pronunciation: \ˈmak-yə-lə\

Function: noun
pl -lae
Pronunciation: \-ˌlē, -ˌlī\
also -las

1: any spot or blotch; esp: see: macule 2
2: an anatomical structure having the form of a spot differentiated from surrounding tissues: as
a: see: macula acustica
b: see: macula lutea

Macular Degeneration

macular degeneration
Function: noun
: progressive deterioration of the macula lutea resulting in a gradual loss of the central part of the field of vision; esp: see: age-related macular degeneration


Function: noun
: see: myopia


Function: noun
: vascularization esp. in abnormal quantity (as in some conditions of the retina) or in abnormal tissue (as a tumor)

Optic Nerve

optic nerve
Function: noun
: either of the pair of sensory nerves that comprise the second pair of cranial nerves, arise from the ventral part of the diencephalon, form an optic chiasma before passing to the eye and spreading over the anterior surface of the retina, and conduct visual stimuli to the brain —called also second cranial nerve


Function: noun
: a cataract operation in which the diseased lens is reduced to a liquid by ultrasonic vibrations and drained out of the eye


Pronunciation: \-kō-ˌag-yə-ˈlā-shən\

Function: noun
: a surgical process of coagulating tissue by means of a precisely oriented high-energy light source (as a laser beam)


Pronunciation: \-ˈsep-tər\

Function: noun
: a receptor for light stimuli

Retinal Detachment

retinal detachment
Function: noun
: a condition of the eye in which the retina has separated from the choroid —called also detached retina, detachment of the retina


Pronunciation: \ˌret-ən-ˈäp-ə-thē\

Function: noun
pl -thies
: any of various noninflammatory disorders of the retina including some that cause blindness <diabetic retinopathy>


Pronunciation: \ˈräd\

Function: noun

1: a straight slender pole or bar
2: any of the long rod-shaped photosensitive receptors in the retina responsive to faint light compare cone 2a
3: a bacterium shaped like a rod


Pronunciation: \skə-ˈtō-mə\

Function: noun
pl -mas
or -ma*ta
Pronunciation: \-mət-ə\
: a spot in the visual field in which vision is absent or deficient

Visual Acuity

visual acuity
Function: noun
: the relative ability of the visual organ to resolve detail that is usu. expressed as the reciprocal of the minimum angular separation in minutes of two lines just resolvable as separate and that forms in the average human eye an angle of one minute compare minimum separable minimum visible

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© 2011 Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Inc.

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