What is myopia
Myopia is the
visual defect that causes a difficulty in distance vision leaving a good near
vision. The
amount of myopia is measured , as indeed all other defects of view , in diopters
, plus a myopic eye is greater the diopters of myopia.
What is it?
Myopia is the visual defect that causes a difficulty in distance vision leaving a good near vision. The amount of myopia is measured , as indeed all other defects of view , in diopters , plus a myopic eye is greater the diopters of myopia.
The highest percentage of the defect occurs between the eastern and in particular among the Chinese ( from 50 to 70 % ) and Japanese ( 30%), in the United States and in Europe myopia affects 15-25 % of the population . In Italy affects 20-25 % of subjects , and among these more than 80% has a defect between 1 and 6 diopters.
The causes
The main causes of myopia are three:
- Eyeball longer than normal ;
- Curvature of the cornea or the lens greater than the norm;
- Increase in the refractive power of the lens.
Most of myopia is due to excessive length of the eyeball to which the images are not in focus on the retina but in front of it .
We distinguish mild myopia up to four diopters myopia medium up to eight diopters and exceeded these values it comes to high myopia .
A distinction is also a physiological and a pathological myopia myopia .
The
physiological myopia , the type of far more frequent , is nothing more than a
lack of proportion between the refractive power of the eyeball and its axial
length .
The term of pathological myopia is used to indicate a form of myopia that leads to degenerative changes in the eye and is due to an excessive increase of the diameters eye ( axial myopia ), this type of myopia usually increases rapidly during adolescence and in the past has received the name of progressive myopia or malignant.
The term of pathological myopia is used to indicate a form of myopia that leads to degenerative changes in the eye and is due to an excessive increase of the diameters eye ( axial myopia ), this type of myopia usually increases rapidly during adolescence and in the past has received the name of progressive myopia or malignant.
Myopia, Hyperopia & Astigmatism Explained
The symptoms
The main symptom of myopia is the reduction of visual acuity for distance . For each myopic eye there is a finite distance to the front of the eye which corresponds to a perfect focus on the retina. For example, if a subject has 4 diopters of myopia this distance corresponds to 25 inches in front of the eye. In myopia of low degree then you have a good view of nearby objects without the need for optical correction . In the higher degrees of myopia , however, this point of focus is so close to the eye to make it extremely tiring work prolonged eye at this distance
.
How is it treated ?
The first and most widely used correction for myopia eyewear is as easy to use and not very expensive , but it inevitably involves visual problems that increase the stronger that correct myopia . The resulting image perceived by the subject is in fact made smaller and short-sighted is sharp only in the central portion of the blame for aberrations and distortions caused by the peripheral part of the lens. These drawbacks lead to an incorrect assessment of distances and depth ( shrunk objects appear further away than vice versa enlarged seem closer ) affecting the quality of life of patients who use it .
The main symptom of myopia is the reduction of visual acuity for distance . For each myopic eye there is a finite distance to the front of the eye which corresponds to a perfect focus on the retina. For example, if a subject has 4 diopters of myopia this distance corresponds to 25 inches in front of the eye. In myopia of low degree then you have a good view of nearby objects without the need for optical correction . In the higher degrees of myopia , however, this point of focus is so close to the eye to make it extremely tiring work prolonged eye at this distance
.
How is it treated ?
The first and most widely used correction for myopia eyewear is as easy to use and not very expensive , but it inevitably involves visual problems that increase the stronger that correct myopia . The resulting image perceived by the subject is in fact made smaller and short-sighted is sharp only in the central portion of the blame for aberrations and distortions caused by the peripheral part of the lens. These drawbacks lead to an incorrect assessment of distances and depth ( shrunk objects appear further away than vice versa enlarged seem closer ) affecting the quality of life of patients who use it .
The lenses for
high corrections also require robust to the choice of frames and small without
leaving much freedom of choice to the patient. The
glasses are heavy enough to cause unsightly nasolabial folds and often
constrain the subject in the practice of various sports activities . Have
been studied and developed new materials to produce lenses with such characteristics
as to reduce these drawbacks these lenses are much more expensive and do not
completely solve the aforesaid drawbacks .
The visual quality improves with the application of contact lenses : there is no shrinkage or distortion of the image device , problems are solved by aesthetic and functional nature , it can not be tolerated by all , especially in some conditions of use ( windy environments , dusty , smoky , and extremely hot ) do not guarantee an acceptable tolerability . In addition, because of environmental pollution are increasing considerably intolerance to contact lenses suffer from allergies direct and crusades. If you use too much , given the visual quality and independence that damage, can lead to further structural problems of the cornea ( the limbus sclero - corneal vascularization , endothelial cell loss , irregular astigmatism , etc. ) , stress affecting the lacrimal in addition to the acute problems , sometimes very serious, such as infection, corneal ulcers also perforating corneal central leucomi , etc. .
In
selected cases, there is the possibility of an alternative therapy that
consists of making a visual rehabilitation using biofeedback reflect the retina
to improve visual acuity . The
system used for years with great success in our studies is called Accommotrac @
Vision Trainer ( AVT ) ( www.accommotrac.com ) and is based on principles very
innovative . Its inventor ,
Joseph N. Trachtman
, OD , Ph.D. , formerly known American expert on visual rehabilitation and a
member of the American Academy of Optometry , used a simple system of
biofeedback for the voluntary control of visual function . Biofeedback
is an innovative technique that is based on the continuous extensive monitoring
physiological phenomena that normally escape the voluntary control of the
patient, and in the next exercise to control them .
Biofeedback
has been used successfully for more than 30 years for the voluntary control of
heart rate, blood pressure and all the functions, such as the same vision ,
self-regulated by our autonomic nervous system. With
sophisticated equipment and with appropriate techniques , these functions can
be driven voluntarily and with ease.
In
other words, with this system will re-education teaches the patient how to get
the best visual results from your eyes ; during treatment the person will learn
a new way of seeing more efficient than what he has, will find himself in the
situation of a learner '
motor skills (such as swimming or cycling ) and can not forget it because the
exercise every day. (see visual
rehabilitation )
In myopia the objectives are:
a) improvement of visual acuity with correction ;
b) improvement of visual acuity in natural vision ( without correction ) ;
c ) reduction or elimination of dependence on glasses ;
d ) reduction of the correction ;
e) reduction in the progression of myopia .
And ' well clearing the field right from the illusion of a possible reduction or disappearance of myopia objective : if the eye is already stretched we can not do anything about it or have to resort to surgical treatment with the excimer laser . The training can improve the performance of the mechanisms that the interpretation of retinal images and neuromuscular function .
The indication for treatment should therefore take into account the starting conditions and objectives as possible, in relation to those required by the subject shortsighted.
The treatment will therefore be indicated in the following cases :
Just started myopia or myopic individuals with hints .
It brings the subject to 10/10 without the use of glasses and is trying to combat the progression of myopia .
In myopia the objectives are:
a) improvement of visual acuity with correction ;
b) improvement of visual acuity in natural vision ( without correction ) ;
c ) reduction or elimination of dependence on glasses ;
d ) reduction of the correction ;
e) reduction in the progression of myopia .
And ' well clearing the field right from the illusion of a possible reduction or disappearance of myopia objective : if the eye is already stretched we can not do anything about it or have to resort to surgical treatment with the excimer laser . The training can improve the performance of the mechanisms that the interpretation of retinal images and neuromuscular function .
The indication for treatment should therefore take into account the starting conditions and objectives as possible, in relation to those required by the subject shortsighted.
The treatment will therefore be indicated in the following cases :
Just started myopia or myopic individuals with hints .
It brings the subject to 10/10 without the use of glasses and is trying to combat the progression of myopia .
a) up to 2-3 diopters : it reduces the correction , it improves natural vision up to 6-8/10 so as to limit the use of glasses to situations that require a clear vision at distance ( for example the guide especially night , the blackboard , the cinema, etc. . ) .
b ) Apart from the 3 diopters : it can reduce the correction and enhance the natural vision up to make the subject independent of the correction in environments known or under conditions that do not require a clear view of the details at a distance ( for example in the home, office in his spare time : the sea, the pool, the gym, etc. . ) .
Myopia who had worsening .
Retrieving the 10/10 with correction in use, thus avoiding the increase . Automatically is increased by the natural vision and therefore reduced the dependence on the correction .
For those who decide they want to be independent of glasses or contact lenses,
you may use the correction with excimer laser ( for defects mild and medium ) or surgical correction ( for defects high ) .
Retrieving the 10/10 with correction in use, thus avoiding the increase . Automatically is increased by the natural vision and therefore reduced the dependence on the correction .
For those who decide they want to be independent of glasses or contact lenses,
you may use the correction with excimer laser ( for defects mild and medium ) or surgical correction ( for defects high ) .
Surgical correction of myopia :
- PRK
- LASIK
- Radial keratectomy
- Implantation of intraocular lens
- Replacement of the lens ( Lensectomy )
Myopia Definition
Myopia is the medical
term for nearsightedness. People with myopia see objects more clearly when they
are close to the eye, while distant objects appear blurred or fuzzy. Reading
and close-up work may be clear, but distance vision is blurry.
Description
To understand myopia it
is necessary to have a basic knowledge of the main parts of the eye's focusing
system: the cornea, the lens, and the retina. The cornea is a tough,
transparent, dome-shaped tissue that covers the front of the eye (not to be
confused with the white, opaque sclera). The cornea lies in front of the iris
(the colored part of the eye). The lens is a transparent, double-convex
structure located behind the iris. The retina is a thin membrane that lines the
rear of the eyeball. Light-sensitive retinal cells convert incoming light rays
into electrical signals that are sent along the optic nerve to the brain, which
then interprets the images.
In people with normal
vision, parallel light rays enter the eye and are bent by the cornea and lens
(a process called refraction) to focus precisely on the retina, providing a
crisp, clear image. In the myopic eye, the focusing power of the cornea (the
major refracting structure of the eye) and the lens is too great with respect
to the length of the eyeball. Light rays are bent too much, and they converge
in front of the retina. This inaccuracy is called a refractive error. In other
words, an overfocused fuzzy image is sent to the brain.
There are many types of
myopia. Some common types include:
- Physiologic
- Pathologic
- Acquired.
By far the most common
form, physiologic myopia develops in children sometime between the ages of 5-10
years and gradually progresses until the eye is fully grown. Physiologic myopia
may include refractive myopia (the cornea and lens-bending properties are too
strong) and axial myopia (the eyeball is too long). Pathologic myopia is a far
less common abnormality. This condition begins as physiologic myopia, but
rather than stabilizing, the eye continues to enlarge at an abnormal rate
(progressive myopia). This more advanced type of myopia may lead to
degenerative changes in the eye (degenerative myopia). Acquired myopia occurs
after infancy. This condition may be seen in association with uncontrolled
diabetes and certain types of cataracts. Antihypertensive drugs and other
medications can also affect the refractive power of the lens.
Genetic profile
Eyecare professionals have debated the role
of genetics in the development of myopia for many years. Some believe that a
tendency toward myopia may be inherited, but the actual disorder results from a
combination of environmental and genetic factors. Environmental factors include
close work; work with computer monitors or other instruments that emit some
light (electron microscopes, photographic equipment, lasers, etc.); emotional
stress; and eye strain.
Myopia is the most common eye disorder in
humans around the world. It affects between 25% and 35% of the adult population
in the United States and the developed countries, but is thought to affect as
much as 40% of the population in some parts of Asia. Some researchers have
found slightly higher rates of myopia in women than in men.
Treatment
People with myopia have
three main options for treatment: eyeglasses, contact lenses, and for those who
meet certain criteria, refractive eye surgery.
Eyeglasses
Eyeglasses are the most common method used
to correct myopia. Concave glass or plastic lenses are placed in frames in
front of the eyes. The lenses are ground to the thickness and curvature
specified in the eyeglass prescription. The lenses cause the light rays to
diverge so that they focus further back, directly on the retina, producing
clear distance vision.
Contact lenses
Contact lenses are a second option for
treatment. Contact lenses are extremely thin round discs of plastic that are
worn on the eye in front of the cornea. Although there may be some initial
discomfort, most people quickly grow accustomed to contact lenses. Hard contact
lenses, made from a material called PMMA, are virtually obsolete. Rigid gas
permeable lenses (RGP) are made of plastic that holds its shape but allows the
passage of some oxygen into the eye. Some believe that RGP lenses may halt or
slow the progression of myopia because they maintain a constant, gentle
pressure that flattens the cornea. As of 2001, the National Eye Institute is
conducting an ongoing study of RGP lenses called the Contact Lens and Myopia
Progression (CLAMP) Study, with results to be published in 2003.
Refractive eye surgery
For people who find glasses and contact
lenses inconvenient or uncomfortable, and who meet selection criteria regarding
age, degree of myopia, general health, etc., refractive eye surgery is a third
treatment alternative. There are three types of corrective surgeries available
as of 2001: 1) radial keratotomy (RK), 2) photorefractive keratectomy (PRK),
and 3) laser-assisted in-situ keratomileusis (LASIK). Refractive eye surgery
improves myopic vision by permanently changing the shape of the cornea so that
light rays focus properly on the retina.
These procedures are performed on an
outpatient basis and generally take 10-30 minutes. LASIK is approved by the
FDA, though certain lasers are in various stages of approval at a given time.
Patients should check with the FDA and ask for patient references when choosing
a LASIK provider.
i-LASIK Procedure Explained
Alternative treatments
Some eye care
professionals recommend treatments to help improve circulation, reduce eye
strain, and relax the eye muscles. It is possible that by combining exercises
with changes in behavior, the progression of myopia may be slowed or prevented.
Alternative treatments include: visual therapy (also referred to as vision training or eye exercises); discontinuing
close work; reducing eye strain (taking a rest break during periods of
prolonged near vision tasks); and wearing bifocals to decrease the need to
accommodate when doing close-up work.
Myopia Prevention Animation
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