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 enjoying 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.
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 from its attachment to 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 its 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.