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Seasonal
or atopic. The eye is covered in a thin, transparent mucus membrane called
the conjunctiva. The conjunctiva contains mast cells. When an allergan comes
into contact with a mast cell, it literally explodes, releasing histamine.
Histamine causes dilation of blood vessels and leakage of clear plasma from
the capillaries. This causes the classic symptoms of redness, itching, and
swelling.
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Reduced
visual acuity from a number of causes, but typically caused by early visual
deprivation or high refractive error. Early diagnosis and treatment before
the age of 5 years can lead to a successful outcome.
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Best-Corrected
Visual Acuity – BCVA |
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The best
Snellen acuity that can be obtained with correction. BCVA can be reduced
following keratofractive surgeries and certain eye diseases such as keratoconus,
macula degeneration, and optic nerve disease.
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The quality
of vision obtained when both eyes are working together as a team. The advantages
of binocular vision are better visual acuity and fine depth perception,
called stereopsis.
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CK |
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Acronym
for Conductive Keratoplasty, a non-incisional technique that involves the
local heating and reshaping of corneal tissue to alter its refractive properties.
Microwaves are applied very precisely to localized areas of the cornea in
a circular pattern in order to shrink the collagen. This produces a steepening
effect in the center. CK is approved only for the temporary reduction of
farsightedness and for the temporary reduction of presbyopia in one eye
only.
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CLE |
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Acronym
for Clear Lens Extraction, the procedure whereby the natural lens of the
eye is removed to correct high myopia. For example, if the power of the
natural lens is approximately +12 diopters, then its removal will result
in a one-to-one reduction in myopia of 12 diopters. However, when a CLE
is performed in a young patient without presbyopia, the patient will lose
the ability to see up close. The risks of a CLE are about the same as with
any cataract surgery.
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Cataracts |
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Clouding
of the crystalline lens due to age, trauma, certain eye diseases, drugs
or radiation.
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Color
Blindness |
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A congenital
loss of the inability to discriminate between various colors or shades of
colors. Can range from mild to severe, and is typically congenital. It is
much more prevalent in males (X-linked).
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Contrast
Sensitivity |
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The ability
to perceive different spatial frequencies under conditions of varying contrast.
An example of high contrast and high spatial frequency would be the 20/20
letter on a well-lit eye chart. An example of low contrast and low spatial
frequency would be the ability to discern facial features under dim illumination.
A loss of contrast sensitivity often occurs following keratorefractive surgeries
such as LASIK, PRK, RK as well as certain eye diseases.
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Depth
Perception |
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There are
two kinds of depth perception: stereopsis and monocular. Stereopsis is the
ability to perceive objects in 3D, or three dimensions. It can only occur
when both eyes are working as a team. Other depth cues, such as shadow,
relative size, relative motion, are called monocular cues because binocular
vision is not required.
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Diabetic
Retinopathy |
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Diabetes
is a disease causing breakdown of the blood vessels and capillaries within
the body. This can lead to small microaneurysms and hemorrhages in the retina,
called background diabetic retinopathy. When severe oxygen deprivation occurs,
new vessels are formed on the surface of the retina. This is called neovascularization.
The new vessels are fragile and bleed. This is called proliferative diabetic
retinopathy. At some point, intervention with laser treatment can prevent
further neovascularization and hemorrhaging. Called “panretinal photocoagulation,”
the aim is to destroy healthy retinal tissue to reduce oxygen demand.
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Double
Vision |
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When the
eyes do not line-up with the object of regard, double vision can be the
result. This is called binocular diplopia. This is caused by the images
falling on non-corresponding points of the two retinas. When a double image
is perceived by one eye only, it is called monocular diplopia. Monocular
diplopia can result from a distortion of the optical media, such as high
astigmatism or corneal warpage, or a cataract.
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Dry
Eyes |
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The tear
film is a complex layer of lipid, aqueous, and mucus components, and many
other biochemical constituents. Those substances are secreted by a number
of different glands. The major lipid glands are the meibomian glands of
the eyelids. The major aqueous-secreting gland is the lacrimal gland, located
upper-outer quadrant of the orbit, and the various small accessory glands
throughout the conjunctiva. Dry eye can result when any of the constituents
is altered in terms of quantity or quality. Causes of dry eye are manifold,
and include certain drugs such as antihistamines, Acutane, Retin-A, autoimmune
diseases such as arthritis, or common hormonal changes. Dry eye is much
more prevalent in women.
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Eyestrain |
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Also called
“asthenopia.” Symptoms can range from mild discomfort to eye
pain to headaches. This can be due to uncorrected refractive error or simply
over-use of the eyes in stressful situations, such as prolonged reading
or close work.
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Focusing
Disorder |
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Accommodative
insufficiency, accommodative infacility, or accommodative spasm are all
disorders of the focusing system. The most common focusing disorder is simply
due to the aging of the eye and is called presbyopia. Other forms are due
to uncorrected refractive error, such as hyperopia(farsightedness), certain
drugs such as atropine, antihistamines, and antidepressants, or genetic.
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GASH |
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An acronym
used to describe the visual phenomena resulting from keratorefractive surgeries
such as LASIK, PRK, and RK. It stands for Glare, Astigmatism, Starbursting,
and Halos. The GASH symptoms are more intense, or likely to occur under
conditions of low light when the pupils dilate. It is generally accepted
that GASH symptoms are the result of a mismatch between the ablation zone
or correction zone of the surgery and the pupil. RGP contact lenses are
generally effective in resolving this problem. Additional surgeries are
occasionally helpful
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Genetic
Eye Diseases and Dystrophies |
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These
can effect the cornea, the retina, or any part of the eye.
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Glaucoma |
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Not a single
disease, but a family of diseases causing blindness as a result of pressure-induced
atrophy of the optic nerve. Intra-ocular pressure is the primary risk factor
for the development of glaucoma, but glaucoma can also occur under conditions
of “normal” eye pressure. Certain other predisposing factors
include family history and race. Glaucoma is treated with eye drops or surgery
to lower the intraocular pressure. Loss of nerve function is measured by
visual fields and by observation and measurement of the nerve.
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Hypertensive
Retinopathy |
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Cardiovascular
disease can lead to swelling and hemorrhages in the retina, as well as embolisms
of arteries and veins within the retina. Early signs of hypertension are
often visible within the eye as subtle changes in the appearance of the
arteries and veins.
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ICL |
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Implantable
Contact Lens. Also called a phakic IOL, or phakic intraocular lens, because
it is placed in an eye without removing the natural lens. An ICL is used
to correct high refractive errors such as nearsightedness and farsightedness
that are beyond the safe range of other, non-invasive procedures such as
LASIK or PRK. Complications of ICL implantation include glaucoma, secondary
cataract, and infection.
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ICRS |
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Acronym
for Implantable Corneal Ring Segments. The commercial name for ICRS is Intacs.
Available in various curves and sizes, these acrylic ring segments are implanted
within the cornea to reduce myopia by flattening the center of the cornea.
Another use of Intacs is to improve the vision of patients with keratoconus.
The effects of Intacs are somewhat limited to people with lower amounts
of myopia. Also, the technique lacks the higher precision of other techniques
such as LASIK and PRK. However, the effects are somewhat reversible, and
there is no disturbance of corneal tissue within the optical zone.
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Infection |
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Many
microorganisms can infect the eye. The most common is the viral infection
known as “pinkeye.” Caused by a number of common adenoviruses
and spread through “fomites,” or droplets of saliva, “pinkeye”
is usually of short duration and is self-limiting. Other viruses can cause
more serious eye infections, such as EKC(epidemic kerato-conjunctivitis)
and various herpes viruses such as herpes simplex or herpes zoster(shingles).
These viruses can cause severe swelling, eye pain, and even loss of vision
(seldom with EKC, more common with herpes).
Bacterial eye infections often accompany viral infections because of the
breakdown in the eye’s local immune system. Others occur as primary
infections. The more serious bacterial infections can cause an ulcer.
Ulcerative eye infections are much more common with contact lens wear,
especially overnight lens wear. These must be treated early and aggressively.
Still another type of infection is caused by parasites, such as demodex
follicularum, or acanthamoeba keratitis. The former is a little mite that
infects the eyelids, causing swelling and itching. The latter is a ubiquitous,
but dangerous little amoeba that infects the cornea. It is a rare, but
potentially blinding infection that also seems to have a predilection
for contact lens wearers, especially when exposed to tap water, improperly
disinfected swimming pools, hot tubs, or even contaminated soil. Early
diagnosis and treatment is critical.
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Inflammation |
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Inflammation
is the over-reaction of the body’s immune system, and can affect any
part of the eye. It is characterized by invasion of the affected tissue
by inflammatory cells such as lymphocytes, monocytes, and neutrophils. Inflammation
is caused by infection, allergy, or autoimmune disease.
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Irregular
Astigmatism |
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Astigmatism
that cannot be completely resolved with sphero-cylindrical lenses is called
irregular. Irregular astigmatism is sometimes induced by keratorefractive
surgeries such as LASIK, CK, RK, and corneal transplants. A rigid contact
lens will usually resolve this type of astigmatism.
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LASEK |
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Acronym
for Laser Assisted Sub-Epithelial Keratomileusis, a surgical procedure designed
to reduce or eliminate refractive errors such as nearsightedness, farsightedness,
and astigmatism. The procedure involves removing the top layer of the cornea,
called the epithelium, in one piece instead of the thicker flap as is done
in LASIK. After the excimer laser is applied to remove the desired amount
of corneal tissue, the layer of epithelium is replaced. LASEK is probably
more similar to PRK, in which the epithelium is removed first and them allowed
to re-grow over a period of two or three days. Currently, there do not seem
to be any clear advantages of LASEK over conventional PRK. However, like
PRK, flap complications are avoided.
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LASIK |
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Acronym
for Laser Assisted In-Situ Keratomileusis, a surgical procedure designed
to reduce or eliminate refractive errors such as nearsightedness, farsightedness,
and astigmatism. The procedure is performed by first making a thin flap
of corneal tissue, folding it out of the way, then altering the shape of
the cornea by subtracting tissue using an excimer laser. The flap is then
replaced over the treated area. This method results in more rapid visual
recovery and less discomfort than other refractive surgery methods.
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Learning
Related Vision Disorder |
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A vision
condition can result in retardation of reading skills. Reading involves
a complex series of eye movements. Eyestrain from uncorrected refractive
error or a binocular vision disorder can lead to slow and inefficient visual
processing. Visual conditions commonly involved in visual learning disorders
are uncorrected farsightedness and convergence insufficiency.
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Macular
Degeneration |
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The macula
is the part of the retina containing the greatest density of photoreceptors
called cones. Loss of macular function results in loss of visual acuity
in mild forms to a complete loss of central vision, or blindness in more
severe forms. It is the most common cause of blindness in the elderly. Recent
research shows a genetic cause of some forms. While great strides have been
made in the treatment of some forms of macular degeneration, it is still
largely a disease without a cure. Some studies indicate the value of vitamins
and supplements such as anti-oxidants in stabilizing the disease.
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Melanoma
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This is
one of the most common forms of cancer involving the eye. The eye is rich
in the pigment “melanin,” and the melanin-containing cells,
called melanocytes. Melanoma can arise as a primary tumor in the eye, or
as metastatic disease from another part of the body, such as breast cancer.
Regular dilated eye examinations can help detect melanoma in the early stage,
resulting in a better prognosis.
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Optic
Nerve Diseases |
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Besides
glaucoma, there are other diseases that result in inflammation or atrophy
of the optic nerve. Optic neuritis is one of the most common early signs
of MS, or multiple sclerosis. Severe hypertension and certain brain tumors
can cause swelling of the optic nerve. Others, such as coloboma and morning
glory syndrome are congenital.
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Over/under
Correction |
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A result
of refractive surgery in which the target correction is missed. Theoretically,
an enhancement can be performed if the magnitude of the error is sufficiently
large. On the average, 10 percent of laser refractive surgeries will result
in an enhancement. Not all enhancements will result in total resolution.
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PRK |
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An acronym
for Photorefractive Keratectomy, a surgical method of correcting refractive
errors such as nearsightedness, farsightedness, and astigmatism by removing
corneal tissue with an excimer laser. PRK was approved in the U.S. in 1997,
and precedes the development of LASIK. PRK is still very much in use, although
the visual recovery time is longer, and there is more post-operative discomfort.
However, surgical complications involving the LASIK flap are avoided.
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Pink
Eye |
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See Infection,
viral.
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Presbyopia |
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Literally
“aging eye,” presbyopia is the progressive loss of near focusing
ability as a result of continuous changes in the structure and function
of the crystalline lens. While this function begins to decline in late childhood,
the effects are not generally appreciated until the fourth decade, when
the “arms begin to get too short.” The effects of presbyopia
generally peak in the fifth decade. The treatment is reading glasses, bifocals,
bifocal contact lenses, or monovision contact lenses.
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RK |
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An acronym
for Radial Keratotomy, an older surgical procedure for correcting nearsightedness
and astigmatism by making various incisions in the cornea mostly in a radial
pie-shaped arrangement. The technique has largely been abandoned in recent
years in favor of the safer and more precise excimer laser procedures such
as PRK and LASIK.
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Recurrent
Corneal Erosion – RCE |
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The chronic
condition in which an area of the outermost layer of the cornea suffers
from repeated spontaneous and painful erosions, typically on first awakening
when the eye is first opened. RCE can occur in an area of previous trauma
or abrasion in which the epithelial layer heals imperfectly, forming a relatively
loose attachment to its basement membrane. RCE can also occur in epithelial
basement membrane dystrophy, in which there is a genetic or acquired flaw
in the basement membrane in the absence of trauma. Treatment is generally
prophylactic, using light petrolatum ointments, sometimes with sodium chloride
added, at night to prevent adhesion of the epithelium to the inside of the
eyelid.
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Refractive
Conditions – Refractive Errors |
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Also known
as myopia, hyperopia, and astigmatism, or nearsightedness, farsightedness,
and astigmatism respectively. In the new terminology, they are also called
“lower order aberrations.” Myopia results when the image plane
of the eye is located in front of or anterior to the retina. Hyperopia results
when the image plane is located behind or posterior to the retina. Astigmatism,
which may be hyperopic, myopic, or a combination, results when the image
does not fall in a single plane, but is spread out, typically in two major
planes 90 degrees apart. Myopic eyes are typically longer than average,
and hyperopic eyes are shorter than average.
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Retinal
Disorders |
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Holes and
tears can occur spontaneously and lead to a detachment. Various inflammations
infections and inflammations can also affect the retina in addition to tumors
and genetic diseases. The importance of routine dilated eye examinations
in the detection and treatment of retinal disorders cannot be over-emphasized.
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Strabismus |
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The condition
of eye misalignment. Strabismus can either be congenital or acquired. Six
muscles, or extraocular muscles, control eye position and movement. Over-
or under-action of one or more muscles can result in one or both eyes turning
out(exotropia), or turning in(esotropia), or vertically(hypertropia), either
intermittently or constantly. The cause of the improper alignment can be
central, i.e. in the motor center of the brain controlling eye movement.
It can be due to a mechanical restriction within the orbit, or it can be
acquired due to damage to one of the cranial nerves controlling the action
of one or more extraocular muscles. Esotropia is more common in farsighted
children and is often successfully treated with eyeglasses. Some forms of
strabismus respond to visual training, while other forms respond to treatment
with special lenses called prism. Surgery may also be required.
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Styes |
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A bacterial
infection of one of the oil glands in the eyelid, or eyelash follicle. If
located superficially on the margin of the eyelid, it is called an external
hordeolum If located deep within the meibomian gland within the eyelid,
it is called an internal hordeolum. Treatment is usually warm compresses
along with a topical or oral antibiotic.
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Suppression
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Under certain
conditions, the vision in one eye can be suppressed by the brain. This most
often occurs in strabismus, when the eyes are misaligned. Suppression occurs
as a result of the attempt to avoid seeing double. When strabismus occurs
early in childhood, or is congenital, suppression almost always results.
Strabismus acquired in adulthood is not as easily suppressed.
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Tracking
Disorders |
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In reading,
the eyes perform a complex series of quick start and stop movements, called
saccades. When they reach the end of the sentence, they perform a smooth
movement called a return. Efficient readers make fewer saccades and have
fewer returns. Inefficient readers make more frequent stops, taking in fewer
words, tend to re-read the same line, and often lose their place at the
end of the line. Certain vision conditions such as uncorrected refractive
error and binocular vision disorders create tracking difficulties. Other
kinds of eye movements are important for athletic performance. These are
called smooth pursuits. Pursuit movements can also be impaired by vision
disorders. Training can enhance reading efficiency and pursuit movements.
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Trauma |
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Common
injuries are corneal abrasions and conjunctival lacerations. Blunt trauma
can result in hemorrhaging within the eye, as well as retinal tears or detachment.
Early assessment is critical.
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