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Vision screening is aimed at detecting eye disorders of children which are
amenable to treatment in the early years of life. The
American Academy of Ophthalmology and the American Academy of Pediatric
Ophthalmology and Strabismus have issued guidelines to detect such
conditions, namely amblyopia,
strabismus (misalignment of the eyes), and refractive or focusing
errors.
The recommendations begin with an exam for general eye
health in the hospital nursery by a pediatrician or family doctor,
followed by a repeat exam by six months of age.
At age three and a half, children should again be
screened by a pediatrician or an ophthalmologist, with an emphasis on
testing visual acuity, such as by reading an eye chart of pictures or
letters. An evaluation of eye alignment should be performed
and vision should be rechecked at the age of five with subsequent
routine vision exams done in school.
An ophthalmologist should be consulted if any
abnormalities are discovered during these evaluations. An
ophthalmologist should also be consulted if a child has any risk
factors for eye disease such as a history of prematurity, or a family
history of childhood glaucoma, cataracts or eye tumors.
When a child is young, the visual system continues to
mature. Treatment options which may be very effective during
a child's early years may offer little or no benefit later in
life. For this reason, early awareness of eye care and health
certainly can make a difference.
What can you expect when you take your child to the
ophthalmologist? An assessment of vision is the first
step. Each eye will be checked separately. This is
important because a child can function normally even if one eye is
blind, provided that the other eye sees well. Before the
child is able to cooperate with reading an eye chart, the fixation
behavior of each eye on various toys or objects can be
evaluated. The doctor will also check that the eyes are
aligned (i.e., that is there is no strabismus). Strabismus
refers to the condition where two eyes do not point in the same
direction, such as with crossed eyes. The health of the front
portion of the eyes and reactions of the pupils to light will also be
checked.
The next step is usually to dilate the pupils.
One or two eye drops are placed in each eye and after 20-30 minutes the
pupils are dilated and the muscles inside the eye are
relaxed. This enables the doctor to assess for cataracts and
to view the retina (which is the nerve tissue in the back of the
eye). Even in children unable to speak, the ability of the
eye to focus normally can be assessed with the use of several highly
accurate instruments. This will help determine if the child
needs glasses. After the exam, the pupils will remain
dilated for several hours. This may result in some mild
blurring of near vision as well as sensitivity to sunlight.
Eye glass prescriptions are given to children for a variety of
reasons. A common reason is to improve vision.
Glasses accomplish this simply by focusing images clearly onto the
retina in the back of the eye.
Myopia or nearsightedness, which refers to difficulty
seeing in the distance, is one of the most common conditions requiring
glasses. Myopia typically appears around the age of nine or
ten and in its early stages often does not need correction.
The usual course, however, regardless of whether glasses are prescribed
initially, is for the myopia to increase as the child grows.
The onset and the final level of nearsightedness are hereditary to some
degree.
Astigmatism refers to the eye being out of focus because
the cornea or the front surface of the eye is not perfectly
shaped. Glasses can easily compensate for this distortion and
are prescribed based on the amount of astigmatism and the age of the
child.
Hyperopia or farsightedness is another condition which
may require glasses. Whereas hyperopia in adults may cause
blurring, some amount of hyperopia is actually a normal finding in
children. Unless the amount of hyperopia is very high,
children's eyes can focus clearly despite hyperopia.
Therefore, glasses may not be necessary. This is not the
case, however, if the farsightedness is associated with crossing of the
eyes (see Accommodative Esotropia).
In that situation, farsighted glasses would be required to maintain
straight alignment of the eyes.
Another reason to prescribe glasses is to treat amblyopia or a "lazy
eye." Amblyopia is a condition where the vision pathways
between the eye and the brain do not develop fully because one or both
eyes do not receive the proper visual stimulation. One cause
for this is one eye being out of focus in relation to the
other. For example one eye may have astigmatism while the
other does not. In this instance, vision would be clear with
both eyes open because one eye is perfectly focused. Glasses,
therefore, would be needed to prevent or treat the amblyopia in the eye
which is out of focus.