Eye Care Glossary
A
Accommodation:
The ability of the eye to change focus from distant to near.
This ability is gradually lost after age.
Accommodative
Insufficiency:
Loss of, or less than the age
appropriate amount of accommodation.
Adnexa:
The accessory structures of the eye,
including the eyelids, lacrimal gland, lacrimal ducts, etc.
ALK: Automated Lamellar
Keratoplasty (removal of a part of the central corneal
stroma) to effect a
change on the refractive error.
Amaurosis:
Partial
or total blindness.
Ametropia:
Refractive
condition in which parallel rays do not focus on the retina; manifestation if
refractive error.
Amblyopia:
Often
called "lazy eye". It is a condition in which the best corrected
vision in one eye is poorer than 20/20 (6/6) in the absence of any obvious
structural anomalies or ocular disease.
Amsler Grid:
A handheld chart featuring equally spaced horizontal park and vertical lines,
usually white on black background, used to detect central visual field
defects.
Anisometropia:
A
condition of unequal refractive state for the two eyes.
Anterior chamber:
The
front section of the eye’s interior where aqueous humor flows in and out of
providing nourishment to the eye and surrounding tissues.
Anterior segment:
The
part of the eye anterior to the crystalline lens including the cornea,
anterior chamber, iris and ciliary body.
Antioxidants:
Micro-nutrients
which destroy or neutralize free radicals. Molecules which have been
implicated as one causative factor in the stimulation of abnormal cellular
reproduction (cancer) and cellular destruction (aging).
Aphakia:
The
absence of the eye’s natural crystalline lens, usually after cataract
removal.
Aphakic Spectacles:
Thick,
plus-powered eyeglasses that were once the standard optical correction
following extraction of cataract. The glasses were cumbersome and greatly
distorted peripheral vision. Today, an intraocular lens (IOL) is implanted in
the eye after the cataract is removed to replace the focusing power of the
natural lens eliminating the need for Aphakic spectacles.
ARMD: Age Related Macular
Degeneration:
Degeneration
of the photoreceptors in the macular (central) region of the retina resulting
in decreased central vision.
Asthenopia:
Subjective
symptoms or distress arising from the use of the eyes; as in eyestrain.
Astigmatism:
A
refractive error caused by unequal refraction of light in different meridians,
resulting in a distorted and blurred image.
Astigmatic Keratotomy (AK):
An
incisional refractive surgical technique in which transverse incisions are
made in the cornea to reduce or eliminate astigmatism.
B
Binocular Vision:
The
simultaneous use of the two eyes. Normal binocular vision yields a
stereoscopic image and depth perception.
C
Cataract:
An opacity or loss of transparency of the
crystalline lens which results in loss of light transmission, image
degradation and reduced vision.
Choroid:
The
thin, blood-rich membrane that covers the white of the eyeball; responsible
for supplying blood to the retina.
Ciliary Body:
The
part of the eye that produces aqueous humor.
Conjunctivitis:
Inflammation
of the conjunctiva maybe caused by bacteria, virus, allergens or chemicals.
Conjunctiva:
The
thin transparent membrane overlying the sclera (white part of the eye) and
inside surface of the eyelid.
Convergence/Divergence:
The
turning of the eyes simultaneously inwards/outwards so that they are both
"aimed" towards the object being viewed
Cornea:
The
clear front surface of the eye. The transparent "window" and primary
refractive surface of the eye.
Corneal Curvature:
The
shape of the front surface of the eye.
Crystalline Lens:
The natural
lens of the eye, located behind the pupil, which helps bring rays of light to
focus on the retina, The original state of the lens is transparent, but the
lens becomes cloudy with age (see cataract).
D
Depth Perception:
The ability of
the vision system to perceive the relative positions of objects in the visual
field.
Diopter
A unit measurement of the degree to which light converges or diverges.
Diopters are used to define a lens’s refractive power. Equal to the
reciprocal of the focal length of a lens (in meters), e.g., a 2-diopter lens
brings parallel rays of light to a focus at half a meter.
Diplopia:
A condition in which a single object is perceived as two; also called double
vision.
E
Emmetropia:
Refractive condition in which no
refractive error is present and distant images are focused sharply on the
retina with no need for corrective lenses.
Esophoria:
The
position of the eyes in an over-converged position compensated by the external
eye muscles so that the eyes do not appear turned inward.
Esotropia:
The
position of the eyes in an over-converged position so the non-fixating eye is
turned inward.
Exophoria:
The
position of the eyes in an over-diverged position compensated by the external
eye muscles so that the eyes do not appear turned outward.
Exotropia:
The
position of the eyes in an over-diverged position so that non-fixating eye is
turned outward.
Extra-Ocular/External Ocular
Muscles:
The six
muscles that turn the eyes to position them appropriately for viewing objects
in various fields of view.
Extracapsular Cataract
Extraction (ECCE):
A
surgical procedure which removes the cataractous lens but leaves the rear lens
capsule in place.
F
Functional Visual Disability:
The degree to
which a visual error interferes with a person’s ability to perform normal
daily activities, such as, reading, driving at night, or performing hobbies.
G
Glaucoma:
Characteristic optic nerve damage
often associated with abnormally increased intraocular pressure and loss of
visual field.
H
Hemianopsia:
Loss of one half of the visual field in one or both eyes.
Hyperopia:
Far-sightedness, long-sightedness: A refractive condition
which light entering the eye is focused virtually behind the retina, resulting
in a blurred image.
Hypoxia:
A deficiency of oxygen supply to a
tissue
I
Intraocular Lens (IOL):
A plastic lens
that is surgically implanted to replace the focusing power of the natural lens
of the eye following cataract extraction. There are numerous styles of IOLs,
including foldable IOLs and multifocal IOLs.
Intraocular Pressure:
The internal fluid pressure within the
eye created by the continual production and drainage of aqueous fluid in the
anterior chamber.
Iris:
Pigmented tissue that lie behind the
cornea that gives color to the eye (e.g., blue eyes) and controls the amount
of light entering the eye by varying the size of the black pupillary opening.
K
Keratitis:
Inflammation of the cornea.
L
Laser Assisted In Situ Keratomileusis (LASIK):
Laser Assisted
In Situ Keratomileusis, or LASIK, combines excimer laser PRK with elements of
ALK used to reduce refractive error.
Lens: (also called crystalline
lens):
The transparent structure inside the
eye that focuses light rays onto the retina.
M
Macula:
The portion of the eye that allows us to see fine
details clearly.
Macular Degeneration:
Degeneration in the macular region of
the retina that results in decreased central vision and sometimes in
blindness.
Macular Edema:
A collection of fluid in and under the
macular portion of the retina.
Miosis:
Pupillary constriction.
Mydriasis:
Pupillary dilation.
Myopia:
Nearsightedness, short-sightedness
(UK): A refractive condition in which light entering the eye is focused short
of the retina, resulting in blurred image.
N
Near Point Of Accommodation:
The closest point in front of
the eyes that an object may be clearly focused.
Near Point Of Convergence:
The maximum extent the
two eyes can be turned inward.
Neovascularization:
The formation of new
blood vessels, often fragile and inappropriate for the location.
Nystagmus:
A rapid,
repetitive, involuntary movement or rotation of the eyes.
O
Ocular Hypertension:
High ( greater than 21 mm Hg) intraocular pressure.
Ophthalmologist:
A physician
specializing in medical and surgical treatment of eye diseases and disorders.
Optic Nerve:
A bundle of
more than 1 million nerve fibers that connects the retina with the brain. The
optic nerve is responsible for interpreting the impulses it receives into
images.
Optic Neuritis:
A Condition of
inflammation of the optic nerve.
Optometrist:
A
physician who treats refractive errors and eye diseases.
Ophthalmoscopy:
A non-surgical
procedure using contact lenses to alter the shape of the cornea to effect a
change in the refractive error.
P
Papilledema:
Non-inflammatory
swelling/elevation of the optic nerve due to increased intracranial pressure.
Phacoemulsification (fay-koh-ee-mul-sih-fih-KAY-shun):
A form
of extracapsular cataract extraction in which an ultrasonic instrument is used
to shatter and break up a cataract, making it easier to remove.
Photophobia:
Sensitivity
to light.
Photorefractive Keratotomy
(PRK):
A
technique employing an excimer laser to reshape the surface of the cornea and
thereby reducing nearsightedness.
Pingecula:
A
(usually) irritation caused by degeneration of the conjunctiva resulting in a
thickening and yellowing of the normally thin transparent tissue.
Posterior Capsular
Opacification (PCO):
Opacification
of the posterior lens capsule following cataract extraction. Sometimes called
"after cataract," and may cause blurred vision.
Posterior Chamber:
The back section of
the eye’s interior.
Posterior Segment:
The
part of the eye posterior (behind) to the crystalline lens, including the
vitreous, choroid, retina and optic nerve.
Posterior Vitreous Detachment
(PVD):
The
separation of the vitreous body form it’s attachment from the retinal
surface due to shrinkage from age, degenerative or inflammatory conditions or
trauma.
Presbyopia:
Loss
of accommodative ability as the eye fails to allow for the focusing of near
objects, resulting from age-related changes in the crystalline lens or ciliary
muscle.
Prism:
An
optical element which deviates the path of light.
Ptosis:
Drooping
of the upper or lower eyelid from it’s normal position.
Pupil:
The
center hole in the iris through which light must pass to reach the back of the
eye.
Pupillary Response:
The
constriction and dilation of the pupil due to stimulation by light of
accommodation.
R
Radial Keratotomy (RK):
A surgical
procedure using diamond scalpel blades to create linear incisions into the
cornea which result in the flattening of the tissue and thereby altering the
refractive error.
Refraction:
A
determination of the optical error of the eye.
Refractive Error:
The degree to
which images received by the eyes are not focused on the retina, e.g.: myopia,
hyperopia, astigmatism.
Retina:
The thin
neurological tissue which line the back wall of the eye which receives light
and converts it to electrical signals for transmission via the optic nerve to
the brain.
Retinal Detachment:
A separation of
the retina from the back wall of the eye. Results in loss of vision in the
detached area. Repairable with fair to good prognosis for vision in the early
stages.
S
Sclera:
The white
visible portion of the eyeball. The muscles that move the eyeball are attached
to the sclera.
Scotoma:
An area
of partial or complete loss of vision surrounded by an area of normal vision.
Strabismus:
The
condition in which binocular fixation is not present; commonly referred to as
"cross eyed".
Stereopsis:
The
ability to perceive three dimensional depth.
Suppression:
The
inability to perceive all or part of objects in the field of vision of one
eye.
Suspensory Ligament of Lens:
A
series of fibers that connect the ciliary body of the eye with the lens,
holding it in place.
T
Tonometry:
A
procedure for the measurement of intraocular pressure.
U
Ultraviolet Radiation:
Radiant
energy with a wavelength just below that of the visible light. UV-c is the
shortest wavelength at 200-280nm and is absorbed by the atmosphere before
reaching the surface. Extremely damaging to living tissue. UV-b, at 280-315nm
is "burning rays" of the sun and is damaging to most living tissue.
UV-a, at 315-400nm are "tanning rays" of the sun and is somewhat
damaging to certain tissues, UV radiation has been described as a contributing
factor to the processes which result in ARMD and cataracts.
V
Vision Therapy:
(Orthopedics,
vision training, eye exercises) a treatment process for the improvement of
visual perception and / or coordination of the two eyes for efficient and
comfortable binocular vision.
Visual Acuity:
A
measure of spatial resolution. The measure of the ability to visually
discriminate.
Visual Field:
The
area or extent of space visible to an eye in a given position of gaze.
Vitreous Body:
A
clear, jelly-like substance that fills the center of the eye.
Vitreous:
The
gel-like transparent fluid substance filling the posterior four fifths of the
globe between the crystalline lens and retina.
Y
YAG Laser:
The YAG
Laser is an instrument that emits a short pulsed, high energy light beam that
can be precisely focused to cut, vaporize, or fragment tissue.
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