The aegis & intelligencer. [volume] (Bel Air, Md.) 1864-1923, 1900-08-17
THE EYES MUSCLES.
HOW THEY OPERATE AND CONTROL
OUR ORGANS OF VISION.

Why Your Eyes Sometimes Hurt and
the Letters Seem to "Swim" When
You Attempt to Keep on With Your
Reading or Writing.
Asthenopia is a condition of the eyes
In which it is impossible to read, write,
draw or do anything involving close APP
plication Of the eyes, at least for any
great length of time. A little work may
be done, but the eyes soon become fa-
tigued-in an hour or two perhaps or in
FIVE or ten minutes in very bad cases
and work has TO be abandoned.
The patient may see as well as any
body at the commencement of The task,
especially if it be essayed soon after ris-
ing, but in little while there is a swim
ming" in the field of view, the printed
letters begin to dance and their edges be-
come thick and indistinct, there is a feel
ing of weight i'll the eyelids and Il flow OF
tears.
Work may be resumed after a pause
but the same symptoms soon recur, and
if work is persisted in a sharp pain is felt
in the temples and around the eyes, espe-
cially near the eyebrows, there is a feel
ing of cramplike contraction at the root
of the nose, the tears flow more cOpiouS-
iy, the eyelids become intiamed and red
dened and so called catarrh of the eyes
ensues.
The characteristic feature of all these
symptoms is that they soon vanish when
work demanding close application of the
eyes is stopped and reappear when such
work is resumed.
The patient usually feels best on Sun
day-that is, if he really makes Sunday
a day of rest-and gets gradually worse
through the week until Saturday night.
when his condition is the worst. The
above are the symptoms of asthenopia,
which Greek word simply means a lack
of visual power and fails to give any idea
of the real nature of the malady.
The causes as well as the varieties Of
asthenopia are many, but the chief OF
these is insufficient power, generally con
genital, of the muscles, and especially of
the muscle whose function it is to turn
the eyeball inward. or toward the nose
1t should be explained that the eyeball.
which is almost a perfect sphere, rolls
on soft cushion of fat within the con-
ical eye socket and is moved in various
ways by six muscles. Four of these, the
straight muscles, or recti, turn it re
spectively up, down, in and out. The
other two, the oblique muscles. pass
through rings of cartilage and are at
tached to the eyeball in such a manner
as to enable them to turn on its axis.
The inner straight muscle, or internal
rectus, is one whose weakness gives rise
to asthenopia. Now. when near object,
such as letter in a printed page, is
looked at attentively both eyes are turn
ed full on it. so that the two lines of
riciar, onfin or tho Ioffar
This turning is effected by the internal
recti muscles referred to. The nearer
the object is the more sharply are the
eyes turned inward and the greater is the
effort required of the inner muscles to
bring the eyes to the right position and
hold them there against the pull of the
other muscles.
1t is evident also that strain and IA
tigue of these inner muscles must in
crease with the length of time that the
eyes are thus fixed on near objects. The
size Of the type also has an indirect eff
feet, because small objects must be held
close to be seen distinctly. If the eye
muscles are strong and healthy and II
there is no abnormal resistance to the
free motion of the eyeball. the eyes may
be used for long time without fatigue,
but when the inner muscles are weak
they cannot stand the strain, and asthe-
nopia results.
The remedy is fortunately very simple
and easily applied. 1t is merely a pair of
prismatic or wedge shaped glasses. Rays
of light passing through glass prism
are bent or refracted toward the base Of
the PRISM or away from its edge, so that
if a prism of small angle is held before
each eye with its base toward the nose
and a near object is looked at through
the prisms the rays by which the object
is seen, though widely diverging at first,
become nearly or quite parallel on trav-
ersing the prisms. Hence the axes of the
eyes may be held nearly or quite parallel
instead of being strongly converged, and
very little strain is put upon the weak in
ternal recti, or converging muscles. OF
course the angle which the prism should
have must be determined in each case by
the oculist.
Shortsighted people who may suffer
from asthenopia caused by holding their
work too close to the eyes do not need
prismatic glasses, but are relieved by
the use of ordinary concave glasses,
which enable them to hold the book far
Their away and thus diminish the con-
vergence of the optic axes.
Now. if the prisms are reversed or
placed with their edges toward the nose
they will clearly act in an opposite way
necessitating stronger conveyance of the
optic axes and increased strain of the
inner muscles.
II it be asked who would be so foolish
as to make the experiment, it may be an
swered that thousands are ignorantly
and unconsciously doing it every day
through the use of i'll fitting spectacles
and eyeglasses. The intended function
of ordinary spectacles is to magnify or
diminish the apparent size of objects, or.
to put it another way, to lengthen or
shorten the focal distance of the eye.
They are not intended to bend the
whole pencil of light to right or left and
thus displace the image as a prism does.
Nor do they have this effect to an appre
ciable extent if the centers of the lenses
are just as far apart as the pupils of the
eyes, so that each eye looks through the
center of it's lens. But suppose the glass
es are convex and are set too far apart.
so that the eyes look through their inner
halves instead of their centers?
Now, half lens-or, indeed. any por-
ton of lens except the center-acts not
only as a lens, but also as a prism and
bends light passing through it toward its
thickest part-that is. toward the center
of the lens. Convex glasses set too wide
apart therefore act like prismS set with
their edges inward and tend to cause
asthenopia. Concave or shortsighted
glasses set too near together have the
same effect.-Philadelphia Press.
Painted Lips.