=Accommodation= in the eye is the ability of the eye to vary its focal
point. When the normal eye (emmetropic) is at rest its focal point is
at infinity so far as parallel rays are concerned. This is called the
far-point or the “=punctum remotum=” (P. R.).
When the eye looks at letters twenty feet away it scarcely accommodates
at all to get a focus, or so little that it may be disregarded in
ordinary practice. Now if one brings fine print close to the eye he
will find a point so close that it becomes indistinct. This point is
the near-point of focus or the =“punctum proximum”= (P. P.). The range
of accommodation is the difference between the refractive power of the
eye when it is at rest and when the accommodation is exerted to the
utmost, the difference between the P. R. and the P. P.
If one must accommodate one diopter to get a focus at one meter or
forty inches distance, at thirteen inches or reading distance one must
accommodate at least 3 D in order to see the letters clearly. If 3 D
were the total of his accommodation he could not read at that distance
but a few minutes; because the accommodation could not be held at its
maximum for long at a time. Eye strain with its train of symptoms would
result. Hence it is quite important to find the near-point or punctum
proximum in order to judge in regard to eye strain in an emmetropic
eye. If there is a refractive error, allowance for it must be made
accordingly.
As a person gets older the accommodation in the eye becomes less
and less until at 45 years of age he can only use 4 to 5 D of
accommodation. This is so close to the amount required for reading
that he has some eye strain. He begins to hold his paper farther away
from him so he requires less accommodation. This condition we call
“old sight” or =presbyopia.= An emmetropic eye at forty-five to fifty
years of age requires a plus glass to make up for some accommodation in
reading.
Frequently there are latent disturbances of equilibrium of the
extrinsic muscles of the eye. This is =heterophoria.= If it is a
latent convergence it is =esophoria=; if a latent divergence it is
=exophoria=. The latter is more frequent. Hyper- and hypophoria are
used for upward or downward tendencies. Normal muscular balance is
=orthophoria=.
Cause the patient to fix on an object about thirteen inches away with
both eyes; push a sheet of paper in front of one eye and watch behind
the paper, the eye thus covered. If heterophoria exists the eye will
move slightly from its point of fixation since it no longer sees the
object. In orthophoria it will remain fixed as long as the other eye
sees the object; the innervation to the different muscles is properly
distributed.
A Maddox rod found in any complete trial case may be placed before one
eye. Have the patient fix on a candle flame, say twenty feet away.
The flame appears drawn out into a luminous line. This line can not
be fused with the candle flame as the other eye sees it if there is
heterophoria. The amount and kind of disturbance is somewhat indicated
by the distance and direction of the luminous line and the flame. The
exact amount can be measured by the use of a prism that will cause them
to fuse.
Next the patient should be taken to the dark room and a careful
inspection of the anterior segment of the eye should be made with
oblique illumination. First use the unaided eye, then use a lens that
magnifies. The 20 D plus lens from your trial case will suffice for the
magnification. Note the transparency or lack of it in the cornea and
crystalline lens; the depth of the anterior chamber and the appearance
of the pupil and iris. Now we are ready for the ophthalmoscopic
examination.
=The Ophthalmoscope.=—This is an instrument that commands great
respect. Any one who is interested in eye troubles must have and use
the ophthalmoscope if he expects to be efficient in diagnosis, upon
which, of course, intelligent treatment must forever depend. One must
try and try again in order to become proficient in the use of the
ophthalmoscope.
A Schematic Eye is of great assistance to a beginner who does not
have clinics or patients on whom to practice. Such an eye with full
directions can be obtained at almost any optical goods store. It will
make the study of ophthalmoscopy easy and interesting. The pupil can
be regulated to any size and the eye can be made short (hyperopic),
long (myopic) or normal (emmetropic) for study.
The efficient use of the ophthalmoscope makes the diagnosis of internal
diseases of the eye as easy as the diagnosis of external diseases of
the eye. Only some rare conditions will puzzle, and that is true of any
part of the anatomy.
The ophthalmoscope is a simple instrument; its chief function is to
illuminate the interior of the eye. The value of ophthalmoscopic
findings depends on their correct interpretation by the examiner.
The ophthalmoscope has a mirror to reflect the light into the eye. It
has two discs on which are mounted convex (plus) and concave (minus)
lenses. The larger disc has seven plus and eight minus lenses. To these
may be added the lenses in the smaller disc making many combinations.
A drop of a 2% solution of cocaine or homatropine may be used as a
mydriatic where one can not otherwise see clearly the fundus. If no
mydriatic is used a somewhat weak illumination should be employed in
order not to arouse the accommodation to much activity and make the
pupil small. If there is any opacity in the media a strong illumination
should be used. The room should be dark; the darker the better.
There are two methods of using the ophthalmoscope. The =indirect= and
the =direct= methods. One is more useful at one time and the other at
another time. By the indirect method we view the whole field of the
fundus more readily but less in detail. With the ophthalmoscope before
his eye the examiner’s face is twelve to fifteen inches from that of
the patient. When the “=red reflex=” of the eye is seen a plus 13 or 16
D lens is interposed near the patient’s eye. This magnifies the field.
The image is inverted. As a rule it is best seen with a +4 D lens in
the aperture of the ophthalmoscope.
This method is especially more satisfactory in high degrees of myopia
and astigmatism. The =optic disc= is the objective point. One may see
a retinal vessel first; this should be followed to its emergence from
the disc. From this point view all parts of the fundus by having the
patient look in different directions. This is better by the indirect
method than for the examiner to vary his position.
The direct method of ophthalmoscopy is better for detail work and in
all cases except high degrees of myopia and astigmatism. It is also
better in determining errors of refraction. The patient looks straight
across the room. For a beginner it may be essential to dilate the
pupil, hence the schematic eye as suggested.
If the examiner has a refractive error, he should wear his own glasses
or correct by throwing in front of his eye proper lenses in the
ophthalmoscope. Face the patient and sit on the side of the eye to be
examined. Use left eye to examine the patient’s left eye and right eye
for the patient’s right. Examiner and patient keep both eyes open. The
examiner may not be able to suppress the image of his other eye and may
have to close it part of the time. Catch the “red reflex” some 15 to 18
inches away and move close to the patient’s eye. The “red reflex” color
varies with the error of refraction, the transparency of the media, the
degree of pigmentation and the size of the pupil. A blood clot will
make it redder, some exudates will make it gray or yellow.
The examiner may approach as close as half an inch from the eye to be
examined. Find the optic disc and examine all points of the fundus from
it. Rotate in glasses to correct the patient’s refractive error if he
has any. The strongest plus glass with which the fine retinal vessels
can be clearly seen will represent the =hyperopia= of the eye. This
is true only if the examiner’s accommodation is at rest. The weakest
minus glass with which the fine retinal vessels can be clearly seen
represents the =myopia=.
=A Normal Fundus.=—The color of the fundus is due to the blood vessels
of the retina and choroid and the connective tissue of the choroid and
sclera. Variation is due to the pigment. In the albino it is light
pink. In the negro it is dark reddish. There are all gradations between
the two.
The =optic disc= is the end of the optic nerve as it comes into the
eye; it is circular in shape, pink in color, and sharply defined. It is
about 1-16th of an inch in diameter; about 15° to the nasal side of the
pole of the eye and slightly above the horizontal. There may be a dark
=choroidal ring= around the disc or part way around. There may also
be a white ring caused by the sclera. As a rule there is a depression
in the center of the disc out of which the retinal vessels emerge and
spread out over the fundus.
The =fovea centralis= or point of clearest vision is located two and a
half disc diameters to the temporal side of the disc. Around this is a
circular area of light yellow, the =macula lutea=.
The subject of ophthalmoscopy has been touched upon somewhat in detail
because of its great importance to the general practitioner. Every
osteopathic physician should know the ophthalmoscope well enough
to recognize the ordinary lesions inside the eye. When we take up
pathological conditions of the eye we will have occasion frequently
to refer to the ophthalmoscopic appearance. Without the use of this
instrument all of our clinical field research on internal diseases of
the eye is valueless. Many have told me they have cured cataract with
osteopathic treatment, some say they have cured specific neuroretinitis
with no sequelæ, others testify to opacities and blindness from
various causes. Invariably we ask if they used the ophthalmoscope in
their diagnosis and with it watched the progress of the case. Almost
invariably the answer is “no, it looked like it,” “the symptoms
indicated it,” or “Dr. so and so, an oculist diagnosed it as such.”
Fellow Osteopaths! we can not base our claims on this kind of data.
With a little study and practice the ophthalmoscope can be mastered.
Not till then can we get reliable statistics on internal diseases of
the eye in our case reports. Osteopathy has much to reveal to us in
this field and for the sake of the science and our patients we appeal
to every one to do the work here set forth.