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Bifocal
glasses are
used to correct vision at two distances—a prescription on top for far away
and a different prescription on the bottom for near.
Most people think of bifocals as reading glasses for people over forty
who lose their ability to focus up close as they age.
But
children can also need reading glasses.
Many
children have not developed sufficient control over their focusing systems,
the natural lens inside the eye that keeps images clear, especially up close.
Some children lack the ability to sustain sufficient focusing over an
extended time period, so after a while print begins to blur.
Others can’t make fast focusing shifts from one distance to another,
like from the board to their desks, so any time they look away, everything is
blurry. Some children have a tendency to over focus, and the
additional stress causes eyestrain and headaches. If they over focus too
much, the additional tension on the visual system can make the eyes to turn
too far inward, causing double vision. Finally, near work at school places
much more stress on the visual system than distance viewing, and some young
children respond by translating the visual stress into physical and emotional
symptoms—back and neck tension, headaches, constriction of their perceptual
fields and a reduction in their visual space, a tendency to develop
nearsightedness, and avoidance of the reading tasks that are causing the
physical and visual discomfort.
Prescribing
reading glasses effectively treats
many of these problems. A convex plus lens relaxes the child’s focusing
system, relieving much of the visual stress. In fact, prescribing a low
power plus lens is so effective in keeping children’s visual system
comfortable during extended close work at school that they are often called
“learning lenses.”
Reading
glasses that use a bifocal are a good option for school-aged children who only
need the additional correction up close. The bifocal gives them the lens
support they need for deskwork but doesn’t change their distance vision.
Sometimes vision therapy is also prescribed when the focusing problem is
severe enough that additional interventions are also required.
 New
advances in lenses allow children flexibility in the type of bifocal they
choose. Many children still prefer the flat-top bifocal because the line
separating the two powers helps them tell exactly where their distance
prescription ends and their near prescription starts. However, some
children or parents don't like the look of the "line", so for them
progressive no-line bifocals are a good option. The lens is made so that
the change between prescriptions is so gradual no line appears. Another
very popular option is the "half-moon" bifocal.
It has the advantage of a clear delineation between powers liked lined
bifocals but when the glasses are on the child's face, the bifocal is
invisible
like progressive lenses.
When
bifocals or reading glasses are prescribed, it is important that children wear
them for all close work, especially at school and during homework. Sometimes
children will only need the bifocals for a few years as they develop control
of their focusing system. Others may need the additional near-point
support for as long as they are in school and spending a lot of time reading.
Bifocals
are an important tool for optometrists when working with children who spend up
to eight hours a day using their eyes for reading and school work. By
adding an additional lens power for up close, optometrists are able to adjust
children’s focusing system to give them better control and eliminate
eyestrain, blurred vision, headaches, and fatigue.
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