Myopia, or nearsightedness, is a condition in which objects in the
distance are blurred either because the eye is too long or too strong. It
is the result of both environmental and genetic factors.
The degree to which one is myopic depends on the powers of the cornea and
the lens of the eye and the length of the eyeball. In a normal eye the
incoming visual images meet on the retina in the back of the eye. If these
visual images converge in front of the retina instead of on the retina,
then one is myopic.
There are several types of myopia, of which simple myopia is the most
common. Individuals with simple myopia have eyes that are either too long
or too powerful. Congenital myopia develops in infants. Individuals with
high myopia, greater than six diopters, can develop pathological changes
in the retina, called degenerative myopia. Nocturnal myopia, another type
of myopia sometimes referred to as "night blindness," is
blurred vision only in darkness. Myopia can also be induced by co-existing
medical problems and drug exposure.
A child's refractive status or power of the eye when he or she
begins school is a good indicator of whether the child will become
nearsighted. Most children are hyperopic, or far-sighted, at birth and
experience a decrease in far-sightedness throughout early childhood.
Myopia is less likely to develop by age 13 if a child still has at least
0.75 diopters of hyperopia at age eight. But if a child has become at
least 0.25 diopters myopic at this age then there is a 60 percent chance
that the child will require spectacle correction for nearsightedness by
Myopia does decreases in later life. This appears not to be related to a
decrease in close work as is often suggested but rather due to some factor
intrinsically related to ageing. It has been hypothesized the power of the
lens of the eye changes in later life.
High myopia has been associated with various syndromes: Ehlers-Danlos,
Marfan, Down, and Stickler syndromes. Myopia is often observed in
(ROP). ROP is seen in 68 percent of infants with low birth weights and
over 80 percent of infants born with ROP will be myopic. The myopia
associated with ROP increases through age five, after which it stabilizes.
Although no gene for myopia has been isolated, heredity is believed to
play a role in myopia. If both parents are myopic, then the odds that the
child will be myopic are as high as 60 percent. This drops to at most 40
percent when only one parent is nearsighted, and for 15 percent of myopic
children, neither parent has myopia. High myopia is especially likely to
have a genetic component.
Overall, 25 percent of those living in the United States are myopic.
Myopia is slightly more prevalent among females than males, and among
those with advanced academic training. Less than 5 percent of five year
olds are myopic, but this percentage increases to 25 percent by late teens
and to approximately 35 percent for young adults and to 42 percent of
those middle-aged. These percentages decrease to 20 percent by age 65 and
to less than 13 percent by age 80.
Myopia is more prevalent in Asian countries; as much as 70 percent of the
Chinese population is nearsighted.
Causes and symptoms
Congenital myopia develops because of an obstruction along the visual
pathway such as cataract. The eye becomes elongated in response to blur
these causes, creating a myopic eye.
A first sign that a child might have myopia is difficulty in seeing things
in the distance, such as the chalkboard. The child may not see things in
the distance as well as a classmate or sibling.
For the 2 percent of the population who are extremely nearsighted, an
inherently weak sclera, whose fibers are not held together tightly, causes
the eye to stretch. This stretching can continue into adulthood,
Other causes of increasing nearsightedness include difficulty with
converging, the process through which the eyes move inwardly together when
reading, and esophoria, the condition in which the eyes are more
comfortable positioned close to the nose. Doing a lot of close work, such
and using the computer for extended periods, may increase myopia for
Causes of induced myopia include cataracts and elevations of blood sugar
in diagnosed or undiagnosed diabetics. Some drugs, such as
, and some
, can induce myopia.
Another cause of increasing myopia is the over wearing of
. Swelling of the cornea can occur if the eye does not have sufficient
oxygen causing a transient increase in myopia. Silicone contact lenses
allow a marked increase in oxygen to reach the eye decreasing the
probability of myopic increases.
For the child with diabetes, fluctuations in blood sugars can cause
swelling of the cornea of the eye, leading to transient increases in
myopia, which stabilize once the diabetes is controlled. But the child may
independently become more myopic later in life.
In the early 2000s, it has been suggested that insulin resistance, which
accompanies type 2 diabetes and prediabetes, may increase myopia in
children and adolescents. The level of insulin-like growth factor binding
protein 3 (IGFBP-3), a hormone that works with insulin to lower blood
glucose levels, is low in individuals who are insulin resistant. This
decreased level, in turn, decreases the sensitivity of ocular tissue to
another compound called retinoic acid, which prevents increases in the
length of the eye. Thus, if insulin levels are higher than normal, the
risk of myopia may be increased.
Asthenopia or a feeling of eye strain is not common in myopia. If a child
complains of eye strain, then usually there is another cause of the eye
strain, including an astigmatism, a condition in which the eye is football
shaped; anisometropia, a condition in which the eyes are of different
powers; or difficulty with focusing.
There are many reasons why a child cannot see well in the distance. Myopia
is the most common cause of distance blur, and since much of what a child
learns comes from vision and visual cues, correction of myopia is
important. Also, problems with vision may be a sign of a more serious
ocular problem, such as cataracts, or of a medical problem, such as
Myopia is diagnosed by determining a child's unaided vision and is
confirmed objectively by the eye care practitioner with various
techniques, including retinoscopy and refraction.
The type and extent of myopia is determined by additional testing. These
tests include an evaluation of the child's binocular vision, his
eye movements, his ability to converge and focus on objects close-up, and
his ocular health. Dilation of the eye allows the doctor to check for
complications of ROP, diabetes, or degenerative myopia. Since children are
capable of over focusing, dilation can help the eye care practitioner
determine a child's true prescription because the drugs used to
dilate also impair this tendency to over focus. Over focusing can cause a
child to appear to be myopic when he or she is actually not.
Myopia is most commonly treated with spectacles or glasses. Myopia in
children does not need to be corrected with glasses, unless either
anisometropia, a condition in which there is a difference of more than
1.00 diopters between the two eyes, or
, a condition in which a child cannot be corrected to 20/20 with
spectacles, is present. As the child enters school, distance vision
becomes critical for learning, and children with prescriptions of at least
1.00 diopter of myopia or who have 20/40 vision or worse should be given
glasses. Once a child is diagnosed with myopia, he or she should be
examined every six months to a year, and each eye should be corrected to
20/20 at each visit. The glasses are then usually worn full time, except
for children with difficulty with convergence (esophoria), who may remove
their glasses for close work.
Some adolescents may want to wear contact lenses. Wearing contact lenses
can improve appearance. Peripheral vision is improved with contact lenses,
especially for those with high degrees of myopia or who have
Rigid gas permeable (RGPs) contact lenses are used to correct myopia. The
rate at which myopia increases may be slowed by RGP lenses. RGPs are also
employed in orthokeratology, a technique in which RGP lenses of gradually
decreasing flatness are worn for specified amounts of time. These lenses,
called ortho-K lenses, flatten the cornea, changing the power of the
cornea over time and decreasing myopia. This effect of ortho-K lenses is
not permanent and an ortho-K lens must be worn periodically or the
original myopia reappears. For some individuals—for example, those
with keratoconnus, a disease of the cornea—RGPs may offer the only
way to correct vision.
For some children the development of myopia may be slowed with reading
glasses or bifocals. If bifocals are prescribed, then either progressive
or no-lines, or a lined bifocal may be given. If a lined bifocal is
prescribed, then the line is always placed higher for the child than for
the adult. This is done to encourage use of the power of the bifocal.
Refractive surgery is also used to correct myopia, but only on fully grown
individuals. A child's eyes change and the
of these procedures have not been established in the growing eye.
The most common surgical procedure performed to correct myopia is laser in
situ keratomileusis (LASIK). Other techniques to correct myopia include
photorefractive keratectomy (PRK), radial keratomy (RK), laser epithelial
keratomileusis (LASEK), intraocular lens
Myopia, or nearsightedness, is a condition of the eye in which
objects are seen more clearly when close to the eye while distant
objects appear blurred or fuzzy.
(Illustration by Electronic Illustrators Group.)
implants and intrastromal corneal rings. Inflammation of the eye,
increased dryness of the eye, and cataracts are some of the risks
associated with refractive surgery.
Cycloplegic drugs, such as atropine, may decrease myopia, but they may
hinder the child's ability to see up close. As of 2004 pirenzepine,
which has shown to decrease the rate of myopia in children without
sacrificing the ability of the child to do close work, is in clinical
Most infants are born far-sighted and eventually reach emmetropia or
normal vision, by age six. Over one third of children go on to become
myopic as adults.
Patients with high myopia, greater than 6.00 diopters, have an increased
risk of developing a retinal tear, hole, or detachment; a posterior
staphyloma; a posterior vitreous detachment; or glaucoma. Rarely are these
pathological changes of myopia seen in children or adolescents. Retinal
detachments and tears are possible, however, in highly myopic children or
adolescents who play contact
. If a retinal problem is diagnosed or suspected, referral to a retinal
specialist is necessary.
For individuals who have difficulty with convergence or focusing or who
are esophoric, close work may increase myopia. Children diagnosed with
these problems would benefit from frequent breaks while doing close work.
Increases in myopia for these children may be slowed with bifocals and/or
removal of glasses for reading and homework.
Since elevated levels of insulin may be associated with increased myopia;
a diet low in those foods that increase insulin secretion, such as refined
carbohydrates, may help decrease myopia.
—The ability of the lens to change its focus from distant to near
objects and vice versa. It is achieved through the action of the ciliary
muscles that change the shape of the lens.
—An eye condition in which there is an inequality of vision
between the two eyes. There may be unequal amounts of nearsightedness,
farsightedness, or astigmatism, so that one eye will be in focus while
the other will not.
—An eye condition in which the cornea doesn't focus light
properly on the retina, resulting in a blurred image.
—A condition in which the lens of the eye turns cloudy and
interferes with vision.
—The natural movement of the eyes inward to view objects
—The clear, dome-shaped outer covering of the eye that lies in
front of the iris and pupil. The cornea lets light into the eye.
—A unit of measure for describing the refractive power of a lens.
—The inner, light-sensitive layer of the eye containing rods and
cones. The retina transforms the image it receives into electrical
signals that are sent to the brain via the optic nerve.
—The tough, fibrous, white outer protective covering of the
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