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20/20
-the expression for normal
eyesight (or 6/6 in countries where metric measurements are used). This notation
is expressed as a fraction. The numerator (1st number) refers to the distance
you were from the test chart, which is usually 20 feet (6 meters). The
denominator (2nd number) denotes the distance at which a person with normal
eyesight could read the line with the smallest letters that you could correctly
read. For example, if your visual acuity is 20/100 that means that the line you
correctly read at 20 feet could be read by a person with normal vision at 100
feet. The Snellen chart, which consists of letters, numbers, or symbols, is used
to test visual acuity (sharpness of eyesight). A refraction test is used to
determine the amount of correction needed for a prescription when treating
refractive error such as astigmatism, myopia, or hyperopia. See “Refraction
Test”.
Ablation Removal.
In vision, ablation refers to the surgical removal of eye tissue to
correct a refractive error such as myopia.
AC/A Ratio-
accommodative convergence / accommodative (measured in prism diopters/diopters).
The convergence response of an individual (amount the eyes turn inward) in
relation to the amount of stimulus of accommodation (eye focusing). The normal
ratio is 4:1.
Accommodation-
(eye focusing) the eye's
ability to adjust its focus by the action of the ciliary muscle, which increases
the lens focusing power. When this accommodation skill is working properly, the
eye can focus and refocus quickly and effortlessly, which is similar to an
automatic focus feature on a camera. The ciliary muscles must contract to adjust
for near vision, which causes the eye’s crystalline lens, which is flexible, to
be squashed. For distant vision, the ciliary muscle must relax and the eye’s
crystalline lens is stretched out. The ability of the eye to accommodate
does decrease with age due to the crystalline lens becoming less flexible
causing a condition called presbyopia. (See "Presbyopia").
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Accommodative Esotropia-
(clinical condition) when an individual is focusing on a near object and his or
her eyes are turning inward too much. It is caused by either uncorrected
hyperopic refractive error and/or a high accommodative convergence/accommodation
(AC/A) ratio. The average age of onset is 2 1/2 years. It is most noticeable
when the child is tired or sick. This is treated with plus lenses (glasses or
contacts) to help straighten the eyes. In some cases, vision therapy and
corrective lenses are prescribed. (Please note that Accommodative Esophoria is a
condition similar to accommodative esotropia but lesser in extent.)
Accommodative Excess (AE)-
This clinical condition is also called accommodative spasm. It is an over
focusing, over stimulation of the focusing action of the crystalline lens
causing an inability to relax the focusing system which may result in blurry
vision when focusing at distance objects. Other symptoms include holding near
work closer than normal, headaches with near work (such as reading or using a
computer), eyestrain associated with near work, and possible double vision.
Clinical signs include: patient accepts more minus on accommodative rock but
blurs with plus lenses, lower NRA than PRA, dynamic retinoscopy findings
indication of over accommodation and/or slow relaxation of accommodation, and
reduced or erratic distance visual acuity. Treatment includes a low plus lens
and/or vision therapy.
Accommodative Fatigue-
This clinical condition is also called Ill-Sustained Accommodation. It is
the inability of the eye to adequately sustain sufficient focusing over an
extended time period. The most common sign or symptom is blurred vision after
prolonged near work such as reading and using a computer. In addition, such
patients often have asthenopia (eyestrain), general fatigue, headaches and
nausea, excess tearing, and an unusual sensitivity to light. Clinical signs
include: normal amplitude of accommodation, decreased PRA, and the patient
generally fails the +/-2.00 D flipper test. Plus lenses (glasses or contacts)
and vision therapy are effective in treating this condition.
Accommodative Infacility-
a clinical condition in which the individual has difficulty changing eye focus
from distance to near. Symptoms include eyestrain associated with near work
(such as reading or using a computer), periodic blurring of distance vision
especially following sustained near visual work, tendency to hold near work
closer than expected, headaches with near work, and possible double vision.
Clinical signs include: patient will have difficulty with both the plus and the
minus lens (fails +/- 2.00 D flipper test), low PRA and NRA, and poor recoveries
on Bell Retinoscopy. Vision therapy is an effective treatment option.
Accommodative
Insufficiency (AI)-
This clinical condition is also called non-presbyopic accommodative
insufficiency. It is an under focusing, a lack of focusing ability at a near
distance. Symptoms include eyestrain, blurred vision, occasional or constant
when doing near work (such as reading or using a computer), occasional unusual
sensitivity to light, excess tearing, headaches, and general fatigue. Clinical
signs include: patient will have difficulty with a minus lens, low amplitude of
accommodation, low PRA and higher NRA. Vision therapy is an effective treatment
option.
Accommodative Vergence-
a convergence
response (to turn the eyes inward) which occurs as a direct result of
accommodation (eye focusing). (See "Vergence")
Acetate-
Type of plastic often used in eyeglass frames.
Acuity-
clearness of eyesight. Depends on the sharpness of images and the sensitivity of
nerve elements in the retina. (See "Near Acuity" and "Distance Acuity")
Add-
prescription strength of a
plus lens which is used for near vision. A plus lens can be added to another
lens such as a minus lens for distance vision. (See "Bifocal Glasses" and
"Presbyopia")
After-image- the eye's ability to still see an image during eye blinks
and even after the viewed object is no longer present. The most common example
is seeing light after the flash of a camera.
AK- (astigmatic keratotomy) Procedure in which a surgeon cuts the cornea
so that is more spherical when it heals, thus reducing astigmatism.
Albinism -
pigmentation is deficient or absent. May occur in skin, hair, and eyes. Ocular
albinism is a pigmentation deficiency occurring mainly in the eyes. Individuals
with albinism including ocular albinism commonly have decreased visual acuity
(20/70 -20/200), strabismus, photophobia, and nystagmus. There is no known
treatment. Individuals may benefit from low-vision aids. Treatment options for
strabismus and nystagmus does apply to these individuals. For more information
about albinism,
click here. (See “Strabismus” and “Nystagmus”)
Alignment-
proper fusing (uniting) of images to each eye.
Amblyopia-
(clinical
condition) reduced visual acuity (poorer than 20/20) which is not correctable by
glasses or contacts and is not caused by structural or pathological anomalies.
This condition is often called “lazy eye” because it is typically the result of
disuse. It is usually marked by blurred vision in one eye and favoring one eye
over the other. About two percent of the population is affected.
Types
of functional (reversible) amblyopia:
-
refractive- anisometropia (the
two eyes have different refractive powers), or other
amblyopiogenic refractive errors (hyperopia, myopia, or astigmatism)
-
strabismic- misalignment of the two eyes in which they point in different
directions
-
form deprivation (may also be referred to as amblyopia ex anopsia)-
caused by conditions that prevent light from entering the eye. These may
include congenital ptosis (droopy eyelid), corneal opacity, or cataract.
Treatment
options for functional amblyopia are eye patching, prescription lenses, prisms,
and vision therapy.
Ametropia- any
optical error such as hyperopia, myopia, or astigmatism. Also called refractive
error.
AMD or ARMD-
(age-related macular degeneration) Disorder characterized by the gradual loss of
central vision due to a damaged macula (which is made up of retinal cones
necessary for sight).
Amplitude of Accommodation (AA)-
a measurement of the eye’s ability to focus clearly on objects at near
distances. This eye focusing range for a child is usually about 2-3 inches. For
a young adult, it is 4-6 inches. The focus range for a 45-year-old adult is
about 20 inches. For an 80-year-old adult, it is 60 inches.
Angle- (angle
In glaucoma), "angle" refers to the drainage channel for the aqueous humor in
the eye; improper drainage can lead to the high intraocular pressure associated
with glaucoma. In narrow-angle glaucoma, the channel is blocked, whereas
open-angle glaucoma has other causes, such as the body producing too much
aqueous humor.
Aniseikonia-
a difference
in the size or shape of two visual images
when the images
should be the same size and/or shape.
Anisometropia- the condition in which the two eyes
have different refractive powers.
Anomalous Retinal Correspondence (ARC)-
a type of retinal projection,
occurring frequently in strabismus, in which the foveae (center of the retina
that produces the sharpest eyesight) of the two eyes do not facilitate a common
visual direction; the fovea of one eye has the same functional direction with an
extrafoveal (non-fovea) area of the other eye.
ANSI Z87.1-
The American National Standards Institute's Practice for Occupational and
Educational Eye and Face Protection; eyewear that meets this standard is
considered safer than eyewear that does not.
Anterior Chamber-
Part of the eye behind the cornea and in front of the iris and lens.
Antioxidant-
Substance that inhibits oxidation and can guard the body from the damaging
effects of free radicals. Molecules with one or more unpaired electrons, free
radicals can destroy cells and play a role in many diseases. Antioxidants may
help prevent macular degeneration and other serious eye diseases.
Antireflective coating-
(AR coating) Thin layer(s) applied to a lens to reduce the amount of reflected
light and glare that reaches the eye.
Aperture Rule-
a stick-like
instrument used in vision therapy to develop convergence and divergence (eye
teaming) skills.
Aqueous Humor-
Clear fluid in the eye that both provides nutrients and determines intraocular
pressure.
Aspheric-
Not quite spherical. Aspheric eyeglass lenses are popular among people who have
strong prescriptions because they are thin and lightweight, and reduce
distortion and eye magnification. Aspheric contact lenses can work as a
multifocal, or to correct a single-vision problem like astigmatism.
Associate of the College
of Optometrists in Vision Development-
individual who is licensed optometrist for at least two years and
provides developmental and behavioral vision care services including vision
therapy. Associate members must obtain at least 10 hours of continuing education
annually in functional / developmental/ behavioral / rehabilitation vision care.
The optometrist has not sat for his/her certification exams, therefore is not
Board
Certified in Vision Development and Therapy.
Asthenopia-
eyestrain, symptoms include excessive tearing, itching, burning, visual fatigue,
and headache. It can be caused from an uncorrected refractive error,
accommodation (eye focusing) disorder, binocularity (eye teaming) disorder, or
by extended, intense use of the eyes.
Astigmatism-
light rays entering the eye do not all meet at the same point (similar to a
frayed string), which results in blurred or distorted vision. An abnormally
shaped cornea typically causes this condition. Occasionally
astigmatism exists in the lens of the eye.
This condition is corrected by a cylindrical (toric) eyeglass or contact lens.
Automated Refractor-
also called auto refractor. This method determines the eye's refractive error and the best
corrective lenses to be prescribed by using
a computerized device that varies
its optical power mechanically and prints out the results.
Axis-
the alignment
of the len’s cylindrical part; used for correcting astigmatism. This measurement
is given in degrees. The values are typically from 90 degrees to 180 degrees.
Band Keratopathy-
Opacity of the eye's stroma
and Bowman's membrane.
Base-Down (BD) Prism- a wedge-shaped lens which is thicker on one edge
than the other. The thicker edge (base) is turned down. Prisms bend light
(opposite direction from its thicker end) so the base-down prism turns the light
upward thus causing the eye to also move up. This prism is used to measure an
eye misalignment and/or treat a binocular dysfunction (eye teaming problem).
Prisms are sometimes added to glasses to help improve eyesight due to a
misalignment or
visual field loss.
Base-In (BI) Prism-
a wedge-shaped lens which is thicker on one edge than the other. The thicker
edge (base) is turned inward, closest to the nose. Prisms bend light (opposite
direction from its thicker end) so the base-in prism turns the light outward
(toward the ear) thus causing the eye to also move outward. This prism is used
to measure an eye misalignment and/or treat a binocular dysfunction (eye teaming
problem). Prisms are sometimes added to glasses to help improve eyesight due to
a misalignment or visual field loss.
Base-Out (BO) Prism-
a wedge-shaped lens which is thicker on one edge than the other. The thicker
edge (base) is turned outward, closest to the ear. Prisms bend light (opposite
direction from its thicker end) so the base-out prism turns the light inward
(toward the nose) thus causing the eye to also move inward. This prism is used
to measure an eye misalignment and/or treat a binocular dysfunction (eye teaming
problem). Prisms are sometimes added to glasses to help improve eyesight due to
a misalignment or
visual field loss.
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Base-Up (BU) Prism-
a wedge-shaped lens which is thicker on one edge than the other. The thicker
edge (base) is turned up. Prisms bend light (opposite direction from its thicker
end (base)) so the base-up prism turns the light downward thus causing the eye
to also move down. This prism is used to measure an eye misalignment and/or
treat a binocular dysfunction (eye teaming problem). Prisms are sometimes added
to glasses to help improve eyesight due to a misalignment or
visual field loss.
Behavioral Optometrist-
also called Functional Optometrist or Developmental Optometrist.
An optometrist who specializes in all aspects of vision as it is related to an
individual's development and to the role of vision in relation to reading,
computer monitor use, and sports. The optometrist may use prescription lenses
and/or vision therapy to improve an individual's visual function and
performance. Behavioral optometry had its origins in orthoptics, which is a
non-surgical treatment for strabismus, and in case analysis systems which were
developed to resolve
eyestrain symptoms that
include excessive tearing, itching, burning, visual fatigue, and headache
in nonstrabismic individuals. Behavioral optometry’s emphasize of visual care is
in prevention, remediation, rehabilitation, and enhancement. (See "Fellow
of the College of Optometrists in Vision Development (FCOVD)")
Bifocal Glasses-
used to correct vision at two distances, composed of two ophthalmic lenses such
as a plus lens for near vision and a minus lens for distance vision.
Bi-lateral Integration/
Gross Motor Coordination-
visual guidance of body movements and the coordination between both sides of the
body.
Binocular Fusion Dysfunction-
a clinical
condition in which the eyes are not working as a team. Vision
therapy is an effective treatment option. (See "General Binocular Vision Disorder")
Binocular Vision-
the simultaneous use of the two eyes.
Binocularity-
the ability to use both eyes as a team and to be able to fuse (unite) two visual
images into one,
three-dimensional image (See “Convergence” and “Divergence”).
Bi – Ocularity-
using both eyes, but not together as a team.
Blepharitis-
Condition characterized by crusting around the eyes upon awakening, itching,
burning, tearing, swollen eyelids and mucus.
Blurred Vision-
lack of visual clarity or acuity.
Botulinum Toxin Type A (Oculinum, Botox®)-
an injection of this poison
has been used as an alternative to conventional surgery in selected strabismic
patients. It causes a temporary paralysis of an extraocular muscle that leads to
a change in eye position. This change has been reported to result in
long-lasting and permanent alteration in eye alignment. Although one injection
is often sufficient to produce positive results, one-third to one-half of
patients may require additional injections. This technique has been most
successful when used in adults with small-angle misalignments. It is not
commonly used in children. This treatment is also used in patients who have
blepharospam (an uncontrollable eye lid spasm).
Bowman's Membrane- Corneal layer between the epithelium and the stroma.
Break Point- the
point at which a person can no longer fuse (unite) two images into one. A blur
point will occur before the this point.
Brewster Stereoscope–
an instrument used in orthoptics/vision therapy to improve eye teaming skills
and near focusing skills. It consists of two parallel viewing tubes with a +5.00
D lens. The distance from the target can be adjusted as well as the pupillary
distance. The Bernell-O-Scope and Keystone Ophthalmic Telebinocular are designed
essentially the same.
Bridge–
The part of eyeglasses that extends across the nose.
Cable temple- Style of eyeglasses that wraps around the ear,
to keep them well-fastened.
Cataract- a
condition of the crystalline lens, in which the normally clear lens becomes
clouded or yellowed, causing blurred or foggy vision. Cataracts may be caused by
aging, eye injuries, disease, heredity, or birth defects. Surgery is a treatment
option. The affected lens is removed and is replaced with a substitute (implant)
lens or with a special type of contact lens. Generally the success rate of
cataract surgery is over 90%, if the eye is otherwise healthy.
Central island- Refractive surgery complication in which the laser leaves
an "island" of corneal tissue in the concave ablation zone. Symptoms include
double vision and distortion.
Cheiroscope- an
instrument used in orthoptics/vision therapy to train binocular skills and
accommodation skills. The Keystone Correct-Eye Scope is an example of a
Cheiroscope.
Choroid- Layer of blood vessels and pigments (usually brown or blue) that
lies beneath the sclera (the white of the eye). Often mistakenly called the
iris.
Ciliary Body -
a structure directly
behind the iris of the eye and contains the ciliary muscle.
Ciliary Muscle- a
band of muscle and fibers that are attached to the lens that controls the shape
of the lens and allows the lens to accommodate (change focus).
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CMV retinitis- (cytomegalovirus retinitis) Serious eye infection usually
found in those with immune problems, such as AIDS patients; symptoms include
floaters, blind spots, blurry vision and vision loss.
Collagen-
Fibrous protein in bones and connective tissue, it is also present in the eye.
One type of vision correction surgery heats collagen around the edges of the
cornea (which lets light into the eye). This procedure reshapes the cornea,
helping it focus light right onto the retina, for clearer vision.
Color Perception Test-
a test that measures the ability to identify and distinguish colors.
Color Vision
Deficiency- also
known as Colorblindness. It is the absence of or defect in the perception
of colors. Color vision is based on perception of red, green, and blue. If there
is a defect in the perception of one of these colors, a color will be perceived
as if it were composed only of the other two colors. Based on the color or
colors for which there is defective perception, a person may suffer from red,
green, or blue blindness. Color blindness in which all colors are perceived as
gray is termed monochromasia. For people with the common, inherited, types of
color deficiency there is no cure.
Comitant Strabismus-
a condition in which the magnitude of deviation remains essentially the same in
all positions of gaze and with either eye fixating.
Computer Vision Syndrome (CVS)-
the complex of eye and vision problems related to near work that are experienced
during or related to computer use. Its symptoms include eyestrain, dry or
burning eyes, blurred vision, headaches, double vision, distorted color vision,
and neck and backaches. The condition is caused by various internal and external
factors. Treatment options may include prescription glasses and/or vision
therapy.
Conductive
Keratoplasty- (CK)
Procedure wherein a surgeon uses radio waves to heat collagen in the cornea's
periphery to shrink it and reduce hyperopia.
Cone – a
receptor cell which is sensitive to light and is located in the retina of the
eye. It is responsible for color vision.
Conjunctiva- Mucous membrane that lines the visible part of the eye and
the inner surface of the eyelid.
Conjunctivitis- an
inflammation of the conjunctiva, the transparent layer covering the inner eyelid
and the white portion (sclera) of the eyeball. Conjunctivitis can be caused by a
virus, bacteria, or fungus (infectious conjunctivitis, or "pink eye", may be
contagious); by allergies to pollen, fabrics, animals, or cosmetics (allergic
conjunctivitis); or by air pollution or noxious fumes such as swimming pool
chorine (chemical conjunctivitis). Symptoms include red or watery eyes, blurred
vision, inflamed inner eyelids, scratchiness in the eyes, or (with infectious
conjunctivitis) a puss like or watery discharge and matted eyelids.
Conjunctivitis is usually treated with antibiotic eye drops and/or ointment.
Convergence-
the ability to use both eyes as a team and to be able to turn the eyes inward to
maintain single vision up close.
Convergence Excess (CE)-
a clinical condition in which the eyes have a tendency to turn excessively
inward when viewing an object at a near distance. Symptoms may include visual
fatigue while reading or using a computer, occasional blurred or double vision,
and inability to comprehend or concentrate while reading. Clinical signs
include: greater esophoria at near than distance, high AC/A ratio, and a high
lag of accommodation. Can be improved with vision therapy and/or glasses. (See
"Esophoria")
Convergence Insufficiency (CI)-
(clinical condition) the inability of the eyes to turn inward and/or sustain an
inward turn. Symptoms include eye strain with reading and using a computer,
headaches, loss of comprehension, difficulty concentrating, blurred or double
vision, and eye fatigue. Clinical signs include: near point of convergence of
greater than 4 inches (10 cm), greater exophoria at near than at distance, and
low AC/A ratio. Vision therapy is an effective treatment option.
Cornea- the
transparent, blood-free tissue covering the central front of the eye (over the
pupil, iris, and aqueous humor) that initially refracts or bends light rays as
light enters the eye. Contact lenses are fitted over the cornea.
Corneal Abrasion-
Tearing or puncture of the cornea. Usually causes pain, tearing, light
sensitivity, and a feeling that something is in the eye.
Corneal Implants-
Devices (such as rings or contacts) placed in the eye, usually to correct
vision.
Corneal Ring-
Type of vision correction surgery where a doctor inserts a tiny plastic ring
into the cornea (which lets light into the eye). This ring reshapes the cornea,
helping it to focus light better onto the retina so you can see better. The ring
can be adjusted and even removed if desired.
Corneal Topography-
Process of using a camera/computer system to map the cornea for refractive
surgery, contact lens fitting and corneal disease management.
Corneal Ulcer-
Wound in the surface of the eye caused by injury, dryness due to lack of tear
production, or infection.
Cover
Test-
a
test of eyeball alignment in which each eye is covered with an occluder (eye
cover) and then uncovered to observe eye movements.
COVTT-
Certified Optometric Vision Therapy Technician. To be certified an
individual must be employed by a Fellow (FCOVD), provide documentation of 2000
hours or 2 years of direct clinical experience in vision therapy; or 1000 hours
of clinical experience if the individual holds an AA degree or higher with
emphasis in the behavioral sciences. Submit written answers to a series of Open
Book Questions dealing with various aspects of vision function, testing and
therapy. Pass an extensive written and oral examination evaluating the
candidate's knowledge and clinical abilities in behavioral vision, vision
development and vision therapy. COVTTs must obtain at least 6 hours of
continuing education annually in functional / developmental / behavioral vision
care.
Cystoid Macular Edema- (CME) Swelling of the eye's macula, caused by an
excessive amount of fluid.
Crystalline Lens-
transparent disc located behind the iris which changes shape to focus on objects
at different distances from the eye.
Cycloplegic Refraction-
one method available to eye doctors to determine the eye's refractive error and
the best corrective lenses to be prescribed if needed. The eye is dilated with
the muscles of accommodation (eye focusing muscles) being temporarily paralyzed
with specialized eye drops or spray (Atropine, Homatropine, Cyclogyl, or
Mydriacyl). This is a good method for non-responsive or non-communicative
patients such as young children. The technique of retinoscopy is used with this
method. (See “Retinoscopy”)
Cylinder Lens- an
ophthalmic lens that has at least one non-spherical surface. Used to correct
astigmatism. The values are typically from -0.75 to -1.25. The cylinder
measurement is given with a "-" sign. (Please note that the sign for myopia
(nearsightedness) is also "-".)
Dacryostenosis- Blocked tear duct, which is
characterized by a lot of tearing.
Depth Perception-
the ability to judge relative
distances of objects. (See "Stereopsis")
Depth Perception Test-
a test to
measure the ability of the vision system to discern the relative distances of
various objects. (Also called a “Stereopsis Test”)
Descemet's Membrane- Corneal layer between the stroma and the
endothelium.
Developmental Disorder-
when a delay in an
individual’s normal development has occurred.
Developmental Vision Analysis-
more comprehensive than a routine eye exam, examination will evaluate all of the
patient's visual abilities such as visual acuity, eye focusing skills, eye
teaming skills, eye tracking skills, visual motor skills, and visual perceptual
skills.
Diabetic Retinopathy- Leaking of retinal blood vessels in advanced or
long-term diabetes, affecting the macula or retina. Vision can be seriously
distorted or blurred.
Diopter (D)- a
measurement of the refractive (light bending) power of a lens or a prism
(pd). The strength of prescription glasses and contacts are measured in these
units. For example a lens that is 0.50 diopter (D) is very weak, where as a lens
that is 10.0 diopter (D) is very strong.
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Diplopia- a single
object is perceived as two rather than one; double vision.
Direct Occlusion-
covering the non-amblyopic eye. (See "Inverse Occlusion" and "Occlusion")
Directionality/Laterality-
directionality relates to the awareness of the relationship of one object in
space to another / laterality relates to the internal awareness of the two sides
of the body. Directionality/Laterality can also be called spatial relations.
Directionality/Laterality
Disorder- a condition in which an individual has poor development of
left/right awareness. Symptoms of this disorder include confusion of right and
left direction and letters and/or numbers reversals. Vision therapy is a helpful
treatment option.
Distance Acuity-
the eye's ability to distinguish an object's shape and details at a far distance
such as 20 feet (6 meters).
Divergence- the
ability to use both eyes as a team and be able to turn the eyes out toward a far
object.
Divergence Excess (DE)-
(clinical condition) the eye's tendency to drift out relative to the direction
of a distant object being viewed. Symptoms include: double vision at distance,
headaches, eyestrain, nausea, dizziness, and blurred vision. Clinical signs
include: exophoria greater at distance than near, high AC/A ratio, and reduced
positive fusional vergence at distance.
Can be improved with vision therapy.
Divergence Insufficiency (DI)-
(clinical condition) the eye's tendency to turn more inward than necessary when
viewing a distant object. Symptoms include: double vision, headaches, eyestrain,
nausea, dizziness, and blurred vision. Clinical signs: esophoria greater at
distance than near, low AC/A ratio, and reduced negative fusional vergence at
distance. Treated with corrective lenses and vision therapy.
Dominant Eye- the
eye that "leads" it partner during eye movements. Humans also have dominant
hand, foot, eye, and side of the brain (not necessarily all on the same side).
Druse- Small yellow or white deposit in the eye. Drusen are sometimes
signs of macular degeneration.
Dry Eye- Lack of sufficient lubrication and moisture in the eye. Most dry
eye complaints are temporary and easily relieved; dry eye syndrome is chronic
and needs more advanced treatment by an eyecare practitioner.
Duction Test- a
test of the eye's ability to turn inward or outward while maintaining single,
binocular vision with the gradual introduction of progressively stronger base-in
or base-out prisms.
Dysphoneidesia-
inability to "sound out" words and poor sight recognition of words.
Dysphoneidesia is a subtype of dyslexia. Its characteristics are a combination
of the other two forms of dyslexia: Dysphonesia and Dyseidetic.
Dysphonesia-
inability to "sound out" words. Dysphonesia is a subtype of dyslexia. Children
with this form of dyslexia have difficulty sequentially analyzing and
remembering what and where the sounds are in words. The resulting phonemic
processing problems make it difficult to sound out new words, learn phonics, and
make them dependent on their sight vocabulary. When they come to an unknown word
they will often substitute a word using context clues. For example, "pony" for
"horse", even though the substituted word doesn't look or sound anything like
the original word. When spelling unknown words it is often difficult to
determine what the original word is. For example, they may write "fmlue" for
"familiar" or "lap" for "lamp". They cannot learn phonics because they cannot
process where the sounds are. Their short term sequential auditory memory can be
poor and result in repeating "8167" as "8671", or remember to go to their room
but forgetting to get the item requested.
Dyseidetic- poor sight recognition of words. Dyseidetic is a subtype of
dyslexia. Children with this form of dyslexia have trouble analyzing and
remembering written symbols. They continue to confuse the orientation. For
example, they will write numbers and letters backwards long after other children
have mastered these skills. They often confuse letter sequences in reading, and
in spelling often get all the letters but in the wrong sequence (spelling "dose"
for "does", "on " for "no", etc.). Their visual memory for words is poor,
and after learning a new word they may fail to recognize that same new word
later in the sentence. They have trouble learning to read and spell phonetically
irregular words. For example, they may read " laugh" as "log" and spell it as
"laff", both of which are phonetically consistent. Their spelling will have many
mistakes, but will be phonetically consistent and one can usually tell what the
word was they were trying to spell. When they are attempting to read an unknown
word they will usually attempt to sound it out and do so very slowly.
Dyslexia – a
specific language-based disorder. The individual has difficulty with letter or
word recognition, spelling, reading, writing, and sometimes naming pictures of
objects.
Dyslexia varies in degree from
mild to very sever.
It is caused by an inability of the brain's language centers to decode print or
phonetically make the connection between the word's written symbols and their
appropriate sounds. Dyslexia is not caused by a vision disorder. Children often
are of normal or above normal intelligence. Dyslexia cannot be cured and will
never be outgrown. Appropriate teaching methods can be taught to help those with
dyslexia overcome their weakness.
Click here for
more information. The Dyslexia Determination test which is used by many
optometrists who specialize in vision related vision problems investigates if
the patient has one of the three forms of dyslexia: Dyseidetic - poor
sight recognition of words, Dysphonesia- inability to "sound out" words, and
Dysphoneidesia - a combination of characteristics from both types. Vision
therapy is NOT considered a direct treatment for dyslexia.
Eccentric Fixation-
the deviating eye does not use the central foveal (center of the retina that
produces the sharpest eyesight) area for fixation. Commonly, individuals with
amblyopia and some individuals with strabismus will have this visual adaptation.
In esotropia, the eccentrically located retinal point used for fixation is
usually in the nasal retina. In exotropia, the eccentrically located retinal
point used for fixation is usually in the temporal retina.
Vision therapy is a treatment
option for those with amblyopia and/or strabismus. It is not a treatment option
for an individual with a fovea that has been destroyed.
Emmetropia- normal
vision, no correction needed. (See diagram of the
eye.)
Esophoria (Eso)-
(clinical condition) a tendency of the eyes to want to turn more inward than
necessary when an individual is viewing an object at near or at distance, which
may cause the individual to experience eyestrain and other symptoms. Symptoms of
basic esophoria include: eyestrain, headaches, blurred or double vision,
apparent movement of print, and difficulty concentrating on and comprehending
reading material. Clinical signs of basic esophoria include: AC/A ratio is
normal, equal esophoria at distance and near, and normal near point of
convergence. Sometimes esophoria is caused by a refractive error such as
hyperopia (farsightedness), and glasses or contacts can correct the problem
alone. However, sometimes vision therapy is needed to to help re-train the eyes
to function more appropriately.
Endothelium- The cornea's inner layer of cells.
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Epithelium- The cornea's outer layer of cells.
Esotropia (ET)-
(clinical condition) a condition in which an eye is turned either constantly or
intermittently inward toward the nose. Esotropia is a type of strabismus. It is
caused by a reduction in visual acuity, reduced visual function, high refractive
error, traumatic brain injury, oculomotor nerve lesion, or eye muscle injury.
Treatment options may include one or more of the following: glasses or contacts,
bi-focal lenses, prisms, vision therapy, surgery, or Botulinum Toxin Type A
(Oculinum, Botox®) injections. In some cases, esotropia is caused by
a refractive error such as hyperopia (farsightedness), and glasses or contacts
alone may allow the eyes to straighten. Vision therapy is most appropriate when
there are small degrees of misalignment. Surgery, to re-position or shorten the
eye muscles, may be required for high degrees of misalignment. If surgery is
required, a combination of surgery and vision therapy often yields the best
results.
Exophoria (Exo)-
(clinical condition) a tendency of the eyes to want to turn more outward than
necessary when an individual is viewing an object at near or at distance, which
may cause the individual to experience eyestrain and other symptoms. Symptoms of
basic exophoria include: eyestrain, headaches, blurred or double vision,
apparent movement of print, and difficulty concentrating on and comprehending
reading material. Clinical signs of basic exophoria include: normal AC/A ratio,
equal exophoria at distance and near, and decreased near point of convergence.
Vision therapy is an effective treatment option.
Exotropia (XT)-
(clinical condition) a condition in which an eye is either constantly or
intermittently turned outward toward the ear. Exotropia is a type of strabismus.
It may also be called divergent strabismus, wandering eye, or wall eye(s). It is
caused by a reduction in visual acuity, reduced visual function, high refractive
error, traumatic brain injury, oculomotor nerve lesion, or eye muscle injury.
Treatment options may include one or more of the following: glasses or contacts,
bi-focal lenses, prisms, vision therapy, surgery, or Botulinum Toxin Type A
(Oculinum, Botox®) injections. Vision therapy is most appropriate
when there are small degrees of misalignment. If surgery is required, a
combination of surgery and vision therapy often yields the best results. For
more information, please
click here. To see the American Optometric Association's guidelines for
vision therapy, please
click here. (See “Strabismus”)
Extraocular Muscles-
the muscles attached to the outside of the eyeball which control eye movement.
Each eye has six muscles (lateral rectus, medial rectus, superior oblique,
inferior oblique, superior rectus, and inferior rectus) that are coordinated by
the brain.
Eye Hand Coordination-
the ability of our eyes to guide our hands, also called visual
motor integration.
Eye Trac-
(equipment) an electronic testing and recording system of eye movements as in
reading.
Eye Tracking- the
ability of the eyes to smoothly and effortlessly follow a moving target.
Eyecare Practitioner- Optometrists (O.D.s) and ophthalmologists (M.D.s)
both practice eyecare, but in different ways: O.D.s (Doctors of Optometry)
examine eyes for both vision and health problems, prescribe glasses, prescribe
and fit contact lenses, and treat some eye conditions and diseases. M.D.s are
medical doctors who examine eyes, prescribe glasses and contacts, treat disease
and perform surgery. Other non-doctor eyecare practitioners include
paraoptometrics, contact lens technicians and opticians.
Facility of Accommodation-
a measure of the ease and
speed of the eye(s) to change focus.
Farsighted- Also called hyperopia. To farsighted people, near objects are
blurry, but far objects are in focus.
Fellow of the College of Optometrists in Vision Development (FCOVD)-
individual who is a licensed optometrist for a minimum of three years and
directly involved in vision therapy for a minimum of 2 years, has completed a
guided study program, submitted evidence of 100 hours of continuing education in
functional vision (and vision therapy), and passed rigorous written, oral,
and clinical examinations. Fellows are Board Certified in Vision Development and
Therapy and must obtain at least 15 hours of continuing education annually in
functional / developmental / behavioral / rehabilitation vision care.
Figure-Ground-
the ability to recognize distinct shapes from their background, such as objects
in a picture, or letters on a chalkboard.
Fine Motor Skills-
the ability to coordinate hand and finger movements.
Fixation- the
ability to direct and maintain steady visual attention on a target. Fixations
are a form of pursuits.
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Fixation Disparity (FD)-
over-convergence or under-convergence, or vertical misalignment of the eyes
under binocular (both eyes) viewing conditions small enough in magnitude so that
fusion is present.
Flap and Zap- Slang for LASIK.
Floaters- also
known as spots, are usually clouded or semi-opaque specks or particles
within the eye that are seen in the field of vision. The eyes are filled
with fluid which maintains the shape of the eye, supplies it with nutrition and
aids in the focusing of light. Often, particles of protein or other natural
materials are left floating or suspended in this fluid when the eye is formed
before birth. If the particles are large or close together, they cast shadows
which make them visible. This is particularly true when nearsightedness occurs
or becomes more severe. In most cases this is normal but floaters can also be
caused by certain injuries, eye disease or deterioration of eye fluid or its
surrounding structures.
Form Constancy-
the ability to recognize two objects that have the same shape but different size
or position. This ability is needed to tell the difference between "b" and "d",
"p" and "q", "m" and "w".
Fovea- center of
the retina that can produce the sharpest eyesight and contains the most cones.
(See
diagram of the eye)
Fusional Vergence-
a convergence response which
serves to maintain (fusion) the union of images from each eye into a single
image. The eyes will turn with a slow smooth tonic movement or a fast jumping
movement called phasic.
Fusional Vergence Dysfunction-
see "General Binocular Vision Disorder".
Fusion- the union
of images from each eye into a single image. There are three degrees of
fusion. 1st
degree fusion is the superimposition of two dissimilar targets. 2nd
degree fusion is flat fusion with a two-dimensional target. 3rd
degree fusion is depth perception (stereopsis) with a three-dimensional target.
Fusion Test-
determines the eyes ability to unite the images from each eye into a single
image.
General Binocular Vision Disorder- inability to efficiently utilize and/or sustain binocular vision.
Symptoms include eyestrain, headaches, decreased comprehension, inability to
concentrate while reading, excessive tearing, and blurred vision. A patient will
have difficulty with both base-in and base-out prisms. Vision therapy is an
effective treatment option.
Glaucoma- Disease characterized by excessive fluid (aqueous humor) in the
eye, high intraocular pressure and vision impairment. Blindness can result.
Graves' Ophthalmopathy- Thyroid-related, autoimmune eye disorder usually
associated with Graves' disease; symptoms include eyelid retraction, bulging
eyes, light sensitivity, discomfort, double vision and vision loss.
Heterophoria-
tendency of the eyes to deviate from their normal position for visual alignment.
This condition may be observed when one eye is covered.
Heterotropia-
the eyes are abnormally turned.
Higher-Order Aberration- Irregularity of the eye other than a refractive
error (myopia, hyperopia or astigmatism). Higher-order aberrations sometimes
affect your vision (such as decreasing contrast sensitivity), and sometimes do
not.
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High Index- Type of lens with a higher index of refraction, meaning that
light travels faster through the lens to reach the eye than with traditional
glass or plastic. It is denser, so the same amount of visual correction occurs
with less material (whether glass or plastic) — so the lens can be thinner.
HTS Computerized Binocular Home Vision Therapy System
- a computer program which is prescribed by an eye doctor. The computer program
is for improving eye tracking, eye teaming, and/or eye focusing.
Hyperopia-
farsightedness, an individual will have difficulty seeing clearly up close.
Light entering the eye focuses behind the retina when the eye is at rest and is
corrected with a plus lens. Vision therapy is not prescribed for hyperopia.
Children, up to about the age of 8 years, are often farsighted.
Hyperphoria- a
condition in which one eye has a tendency to point higher than the other eye,
causing eyestrain. Sometimes improved by prisms in glasses.
Hypertropia-
strabismus, one eye turned in an upward direction.
Hypophoria- a
condition in which one eye has a tendency to point lower than the other eye.
This condition may be observed when one eye is covered.
Hypotropia-
strabismus, one eye turned in a downward direction.
Hysterical Amblyopia-
a non specific
visual loss with an unknown cause. Upon examination the doctor is unable to find
corroborating objective evidence of this abnormality. The most common symptom is
an isolated visual acuity impairment, followed by combined visual acuity
impairment and visual field constriction, and whereas an isolated visual field
constriction occurred most infrequently. This vision loss may be due to
anxiety or emotional repression. (See "Streff Syndrome")
Ill-Sustained Accommodation-
this clinical condition is also called Accommodative Fatigue. It is the
inability of the eye to adequately sustain sufficient focusing over an extended
time period. The most common sign or symptom is blurred vision after prolonged
near work such as reading and using a computer. In addition, such patients often
have asthenopia (eyestrain). Clinical signs include: normal amplitude of
accommodation, decreased PRA, and the patient generally fails the +/-2.00 D
flipper test. Plus lenses (glasses or contacts) and vision therapy are effective
in treating this condition.
Incomitant Strabismus - a condition also known as
Noncomitant Strabismus. It occurs when the magnitude of deviation is not the
same in the different positions of gaze or with either eye fixating. There
is an abnormal restriction to movement or an over-action of one or more of the
extraocular muscles. Generally, the magnitude must change by at least 5 PD to be
incomitant (nonconcomitant).
Intraocular Lens- (IOL) Artificial lens that a cataract surgeon places in
a patient's eye after removing the eye's natural lens. Like a contact lens, it
has a built-in refractive power tailored specifically to the patient's visual
condition.
Inverse Occlusion-
covering the amblyopic
eye. (See "Direct Occlusion" and "Occlusion")
Intraocular Pressure- (IOP) Eye pressure, as determined by the amount of
aqueous humor filling it. High IOP (ocular hypertension) can be a sign of
glaucoma.
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Iris- the colored
part of the eye located between the lens and cornea; it regulates the entrance
of light.
Iritis- Inflammation of the iris.
Keratectomy- Surgical removal of part of the cornea.
Keratitis- Inflammation of the cornea.
Keratoconus- Condition in which the cornea develops a cone-shaped bulge that
can result in major blurring and distortion.
Keratoplasty- Any of several types of corneal surgery, such as shrinking the
collagen to reduce farsightedness or transplanting a new cornea to treat
keratoconus.
keratotomy- Incision of the cornea.
Kinesthesia-
the sensation of bodily position, presence, or movement resulting chiefly from
stimulation of sensory nerve ending in muscles, tendons, and joints.
Lacrimal Plug- Device to block the lacrimal punctum (an
opening at the end of a tear duct), to keep the eye moist.
Lag of Accommodation- a measure of the eye's ability to focus accurately on
a given target. The dioptric difference between the eye's focusing response and
the stimulus to focus.
Laser Photocoagulation- Procedure in which a surgeon uses a laser to
coagulate tissue, usually to seal leaking blood vessels and destroy new ones in
diseases like macular degeneration and diabetic retinopathy.
LASEK- (Laser Epithelial Keratomileusis) Procedure that is similar to
LASIK, except that the surgeon cuts a flap in the epithelium only, instead of
through the epithelium and part of the stroma. LASEK is used mostly for people
with thin or flat corneas who are poor candidates for LASIK, which requires more
corneal tissue for success.
Laser Thermal Keratoplasty- (LTK) Also called Laser Thermokeratoplasty.
Surgery to correct mild farsightedness in people over 40; the doctor uses a
holmium laser to heat the cornea and shrink its collagen.
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LASIK- (Laser-Assisted In Situ Keratomileusis) Surgical procedure in
which a tiny flap is cut in the top of the cornea, underlying corneal tissue is
removed with an excimer laser, and the flap is put back in place. LASIK corrects
myopia and hyperopia.
Lateral Rectus- muscle Muscle that moves the eye away from the nose.
Latent Hyperopia-
hyperopia (farsightedness) is compensated by accommodation and the tonicity
(tension) of the ciliary muscle; identified by cycloplegic refraction. In mild
cases of hyperopia (farsightedness), the eyes are able to compensate without
corrective lenses; otherwise a plus lens (glasses or contacts) is
prescribed. Vision therapy is not prescribed. (See "Hyperopia")
Learning Disability (LD)-
a disorder that affects
people's ability to either interpret what they see and hear or to link
information from different parts of the brain. Learning disabilities can be
divided into five broad categories: speech and language disorders, reading
disorder, arithmetic disorder, writing disorder, and attention disorders. The
term learning disability does not include children who have learning problems
that are primarily the result of visual, hearing, or motor disorders.
Lensometer- also
called Verometer, is a device used to measure the refractive power of
eyeglasses and contact lenses.
Limbus- Boundary area connecting the cornea and sclera; the three form
the eye's outermost layer.
Lipid- A fatlike substance that can collect on contact lenses, making
them uncomfortable.
Low Vision- Also called partial sight. Sight that cannot be
satisfactorily corrected with glasses, contacts, or surgery. Low vision usually
results from an eye disease such as glaucoma or macular degeneration.
Lutein- An antioxidant that is found throughout the body, but is
concentrated in the macula. Lutein is believed to help protect the eyes from
free radical damage caused by the sun's harmful rays.
Macula-
the most sensitive part of the retina that is about the size of a pinhead and is
where our most detailed vision occurs.
Maculopathy- Disease of the macula, such as age-related macular
degeneration.
Macular Degeneration –
a
deterioration of the central portion of the retina known as the macula.
Click here for information.
Malingering- a
voluntary or intentional reduction in visual acuity or other examination data.
Medial Rectus- muscle Muscle that moves the eye toward the nose.
Microcornea- Abnormally small cornea.
Microkeratome- Small instrument that surgeons use to cut the cornea.
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Microstrabimus
– also called microtropia, monofixation syndrome, and small
angle strabismus. A small angle deviation (inward or outward, commonly
inward) that is less than five degrees with some amount of stereopsis (depth
perception) and anomalous retinal correspondence (ARC). Possible mild
amblyopia, eccentric fixation, and/or anisometropia may also be present. It
frequently results from the treatment of a larger-angle deviation (esotropia or
exotropia) by optical correction, vision therapy, pharmacological agents, and/or
extraocular muscle surgery. Treatment for microstrabimus consists mostly of
correcting significant refractive errors and any coexisting amblyopia. The use
of vision therapy and prisms to establish bifoveal fusion has been successful in
selected cases.
Migraine- (ocular) Visual phenomena that may accompany a migraine
headache or that may occur without any headache. They include light flashes,
spots, wavy lines, flickers, zig-zagging lights, semi-circular or
crescent-shaped visual defects and distortions of shapes.
Minus (-) Lens-
concave lens, stimulates focusing and diverges light. The lens is thinner in the
center than the edges. It is used in glasses or contact lenses for people who
are nearsighted (myopia).
Monocular Vision-
only one eye having useful vision.
Myasthenia Gravis- Autoimmune disease sometimes related to thyroid
conditions. Signs are droopy eyelids or double vision that worsen toward the end
of the day.
Myopia-
nearsightedness, an individual will have difficulty seeing clearly at distance.
Light entering the eye focuses in front of the retina when the eye is at rest
and is corrected with a minus lens. A condition known as high myopia occurs when
myopia is greater than 6 diopters. Typically, vision therapy is not prescribed
for myopia.
Near Acuity-
the eye's ability to distinguish an object's shape and details at a near
distance such as 16 inches (40 cm).
Nearsighted- Also called myopia. Condition in which visual images come to
a focus in front of the retina, resulting in defective vision of distant
objects.
Near Point of Convergence (NPC)- the closest point at which the two eyes
can maintain a single united image.
Near Point of Convergence Test-
measures the patient’s ability to point the eyes at an approaching object and to
keep them fixed on the object as it reaches the patient’s nose. Normal
range is 0 to 4 inches away from the nose.
Negative Relative Accommodation (NRA)-
a measure of the maximum ability to relax accommodation while maintaining clear,
single binocular vision.
Neovascularization- Abnormal growth of new blood vessels, such as in an
excessive amount, or in tissue that normally does not contain them.
Nevus- Also spelled naevus. Brown pigmentation resembling freckle or mole
on white of the eye. More often found in dark-skinned people. Sometimes
malignant.
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Nickel- Metallic element used mainly in alloys. Many eyeglass frames are
made of nickel alloy, so people who are allergic should choose a hypoallergenic
substitute, such as titanium.
Normal
Retinal Correspondence (NRC)-
the foveas of the two eyes are corresponding neural points in the
visual cortex and binocular vision can occur.
Nystagmus- rhythmic
oscillations or tremors of the eyes which occur independent of the normal eye
movements. Generally nystagmus is not curable, but it is manageable. Treatments
include prescription glasses or contact lenses, prisms, and vision therapy.
Occlusion-
to block out light. An eye can be completely or partially blocked. This
procedure is used to promote the use of one eye or both eyes. This therapy
procedure may be used for people with amblyopia, strabismus, or closed head
trauma. It may also be used in a vision therapy program for someone with
amblyopia, eye focusing (accommodation) disorder, or poor eye tracking
(oculomotor) skill. An eye patch, black contact, or another device may be
used to block out light from an eye. (See "Direct Occlusion" and "Inverse
Occlusion")
Ocular Motility-
pertaining to binocular
alignment and eye muscle movement. (See "Binocularity", "Strabismus")
Ocular Motor (OM)-
general eye
movement ability, which include pursuits (to visually track and/or follow moving
objects) and saccades (to direct and coordinate eye movement as the eye quickly
and voluntarily shift from one target to another).
Ocular Motor Dysfunction-
poor eye movement skills. Vision therapy is an effective treatment option.
To see the American Optometric Association's guidelines for vision therapy,
please
click here.
(See “Pursuits Dysfunction” and “Saccades Dysfunction”)
Ocular Hypertension- Condition in which the intraocular pressure of the
eye is elevated above normal and which may lead to glaucoma.
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Oculomotor Skills-
the ability to quickly and accurately move our eyes. These are sensory motor
skills that allow us to move our eyes so we can fixate on objects (fixation),
move our eyes smoothly from point to point as in reading (saccades), and to
track a moving object (pursuits). (See "Fixation", “Pursuits” and “Saccades”)
Oculus Dexter (OD)-
right eye.
Oculus Sinister (OS)-
left eye.
Oculus Uterque (OU)-
both eyes.
Ophthalmologist -
a physician (doctor of medicine (M.D.) or doctor of osteopathy (D.O.) who
specializes in the comprehensive care of the eyes and visual system in the
prevention of eye disease and injury. The ophthalmologist has completed four or
more years of college premedical education, four or more years of medical
school, one year of internship, and three or more years of specialized medical
and surgical training and experience in eye care. The ophthalmologist is a
physician who is qualified by lengthy medical education, training and experience
to diagnose, treat and manage all eye and visual system problems, and is
licensed by a state regulatory board to practice medicine and surgery. The
ophthalmologist is the medically trained specialist who can deliver total eye
care: primary, secondary and tertiary care services (i.e., vision services,
contact lenses, eye examinations, medical eye care and surgical eye care), and
diagnose general diseases of the body. An ophthalmologist is not trained to
provide vision therapy.
Ophthalmoscope- a
device used to illuminate the inside of the eye and enlarge the image for
examining the retina, optic nerve entrance, arteries, and veins.
Optic Nerve- is a
bundle of nerve fiber that connects each eye to the brain and transmits images
from the retina to the brain. (See
diagram of the eye)
Optic Nerve Head- Also called optic disk. Circular area where the optic
nerve enters the retina, and the location of the eye's blind spot.
Optician- is a
professional in the field of designing, finishing, fitting and dispensing of
eyeglasses and contact lenses, based on an eye doctor's prescription. The
optician may also dispense colored and specialty lenses for particular needs as
well as low-vision aids and artificial eyes.
Optometric Vision Therapy (VT)-
as defined by the American Optometric Association: Optometric vision therapy is
a treatment plan used to correct or improve specific dysfunctions of the vision
system. It includes, but is not limited to, the treatment of strabismus (turned
eye), other dysfunctions of binocularity (eye teaming), amblyopia (lazy eye),
accommodation (eye focusing), ocular motor function (general eye movement
ability), and visual-perception-motor abilities. Optometric vision therapy is
based upon a medically necessary plan of treatment which is designed to improve
specific vision dysfunctions determined by standardized diagnostic criteria.
Treatment plans encompass lenses, prisms, occlusion (eye patching), and other
appropriate materials, modalities, and equipment. (Vision therapy can also be
called visual or vision training, orthoptics, eye training, or eye exercises.)
Optometrist - a
health care professional who is state licensed to provide primary eye care
service. These services include comprehensive eye health and vision
examinations; diagnosis and treatment of eye disease and vision disorders; the
detection of general health problems; the prescribing of glasses, contact
lenses, low vision rehabilitation, vision therapy, and medications; the
performing of certain surgical procedures; and the counseling of patients
regarding their surgical alternatives and vision needs as related to their
occupations, avocations and lifestyle. The optometrist has completed
pre-professional undergraduate education in a college or university and four
years of professional education at a college of optometry, leading to the doctor
of optometry (O.D.) degree. Some optometrists complete a residency.
Organic Amblyopia-
gradual or sudden loss of central vision (partial loss) affecting visual acuity
with no treatment options.
Types
of organic (irreversible) amblyopia:
-
nutritional amblyopia- vision loss caused by low levels of vitamin B12 due to
poor nutrition and poor absorption associated with drinking alcohol.
-
tobacco-alcohol amblyopia- clinical evidence exists that a nutritional
deficiency is the underlying cause of this vision loss; however, many still
believe that the toxic effects of alcohol and/or tobacco are contributing
factors.
-
toxic amblyopia-
caused by exposure to toxins such as ethambutol, methyl alcohol (moonshine),
ethylene glycol (antifreeze), cyanide, lead, and carbon monoxide.
Orthokeratology- (ortho-k) Procedure in which a doctor fits you with special
gas permeable contact lenses to reshape your cornea and correct errors like
nearsightedness. Often, patients wear the lenses just at night.
Orthophoria (ortho)-
the absence of either esophoria or exophoria. The eyes do not have a tendency to
want to turn more inward than necessary or want to turn more outward than
necessary when pointed on an object.
Orthoptics- the
science of correcting defects in binocular vision. The technique of eye
exercises to correct strabismus (esotropia or exotropia), convergence
insufficiency (exophoria), or convergence excess (esophoria), amblyopia, and
ocular motility disorders. Orthoptics was pioneered by French ophthalmologist
Javal in the mid to late 1800’s. Today ophthalmologists use specialty-trained
healthcare professionals called
orthoptists to evaluate patients and treat them with orthoptics. In America,
the non-surgical technique of orthoptics is less commonly used by
ophthalmologists compared to other countries. Orthoptics is a limited form of
optometric vision therapy.
overconvergence-
Condition in which the eyes come too far inward when focusing on a near object,
resulting in blurring.
Papilla- Small bump where the optic nerve exits the eye.
Paresis- a paralysis that when occurring in ocular muscles causes double
vision when looking in some directions.
Pars Plana- Posterior part of the eye's ciliary body.
Penalization- to
prevent sight out of the good eye and force the weaker, amblyopic eye, to
function. A filter, eye patch, or eye drops such as atropin or miotics are used
on the good eye.
Perceptual Skills-
includes the identification, discrimination, spatial awareness, and
visual-sensory integration. These are visual cognitive skills used to processes
visual information to the brain to be organized and interpreted. (See “Visual
Perceptual Disorder”)
Perimetry- the
measurement of a visual field function (the total area that can be seen while
looking straight ahead) using targets of different sizes and brightness (light
levels). The visual field is measured in degrees. In a normal eye the peripheral
field of vision is about 180 degrees. An instrument called a perimeter is used
for mapping all areas of a person's eyesight, including peripheral (side)
vision. Visual field testing can help detect certain patterns of visual loss,
indicating specific types of eye diseases or vision conditions. It is the single
best test for diagnosing glaucoma.
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Peripheral Vision-
the ability to see or be aware of what is surrounding us, our side vision. (See
"Visual Field".)
Phasic- fast, jump
movement. (See "Fusional Vergence")
Photoablation- Procedure in which a surgeon uses ultraviolet radiation to
remove tissue.
Photochromic- Able to change lens color or darkness/density depending
upon the degree of exposure to light.
Photokeratitis- "Sunburn" of the cornea; symptoms include discomfort,
blurred vision, and light sensitivity. The temporary vision loss that can result
is called "snow blindness."
Photophobia-
unusual sensitivity to light.
Photorefractive Keratectomy-
(PRK) Surgical procedure in which an excimer laser is used to remove corneal
tissue to correct vision problems.
Pingueculum- Yellowish, thickened lesion on the conjunctiva. May be
caused by irritation from sun, dust and wind.
Physiological Diplopia-
a normal diplopia (double
vision) that occurs when an individual is not pointing his/her eyes on a certain
object.
Plano Lens- a lens
that has no prescription. No variance between the curvature of the front and
back lens surfaces. It is a flat lens.
Pleoptics- a
method of eye exercises created to stimulate and train an amblyopic eye. The
goal is to have eyesight which is produced by the fovea. (See "Eccentric
Fixation")
Plus (+) Lens-
convex lens (thicker in the middle) relaxes focusing and converges light. It is
typically used in glasses or contact lenses for people who are farsighted
(hyperopic). Although it may also be prescribed for other visual conditions as
well.
Polaroid Lens- a
lens used in sunglasses and sometimes 3D glasses which consists of two glass or
plastic surfaces with a plastic lamination between the two surfaces, and
designed to reduce reflected glare. In optometric vision therapy, these lens are
used with 3D pictures such as vectograms and stereograms, which are also
polarized.
Polycarbonate- Lens material that is very impact-resistant, thinner than
plastic, and is used for spectacle lenses.
Polymethyl Methacrylate-
(PMMA) Old-fashioned hard contacts were made of PMMA, which is not permeable;
today's rigid lenses contain other polymers that allow oxygen to reach your eye.
Positive Relative Accommodation (PRA)-
a measure of the maximum
ability to stimulate accommodation while maintaining clear, single binocular
vision.
Posterior Chamber- Part of the eye behind the iris and in front of the
lens.
Presbyopia-
sometimes called the fourth refractive error, is not truly a refractive error.
It is the natural process of the eye losing the ability to accommodate or change
the shape of the natural crystalline lens inside the eye to see comfortably at
near. This vision defect occurs with the advancement of age; the onset usually
occurs between the ages of 40 to 45. Unlike the rest of the body, which stops
growing by the age of twenty, the lens of the eye continues to grow throughout
life. As the lens ages and grows, it becomes harder in consistency, loses its
elasticity, and therefore is resistant to changes in shape. The result is a
gradual reduction in accommodation (near eye focus), and a more dependence on
reading glasses. A plus lens or multi-focal lens (such as a bifocal lens) is
prescribed in the form of glasses or contact lenses. For more information,
please
click here. Vision therapy is not a treatment option.
Prism-
a wedge-shaped lens which is thicker on one edge
than the other. This plastic or glass lens bends light (opposite direction from
its thicker end). Prisms can be used to measure an eye misalignment and/or treat
a binocular dysfunction (eye teaming problem). A prism is sometimes added to
glasses to help improve eyesight due to an eye misalignment or
visual field loss.
(See "Base-Down Prism", “Base-In Prism”, “Base-Out Prism”,
"Base-Up Prism", "Yoked Prism")
Prismatic Effect By Lens-
when light goes through a wedge shaped lens which is called a prism, it bends.
Light is also bent when it does not go through the center of a lens. This is an
undesirable effect that can occur in glasses. It commonly occurs when the
pupillary distance (PD) is not measured or made correctly.
Progressive Lenses- (also, progressive addition lenses or PALs)
Multifocal lenses whose corrective powers change progressively throughout the
lens. A wearer looks through one portion of the lens for distance vision,
another for intermediate vision, and a third portion for reading or close work.
Each area is blended invisibly into the next, without the lines that traditional
bifocals or trifocals have.
Propionate- A soft, flexible material that is sometimes used in goggles.
Proximal Vergence-
a convergence response
attributed to the awareness of, or the impression of nearness of an object of
regard. (See "Vergence")
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