A System of Terms relating to 
the Conditions of the Ocu- 
lar Muscles known as 
“ Insufficiencies.” 
BY 
GEORGE T. STEVENS, M. D., Ph.D., 
NEW VOKK. 
REPRINTED PROM 
€Tte XeU) York i&etiical Journal 
for December 4, 1886. Reprinted from the New York Medical Journal 
for December 4, 1886. 
A SYSTEM OF TERMS RELATING TO THE 
CONDITIONS OF THE OCULAR MUSCLES 
KNOWN AS “INSUFFICIENCIES.” 
By GEORGE T. STEVENS, M. I)., Ph. D,, 
NEW YORK. 
The relations of the eyes to each other, in the act of 
vision, exercise important influences, not only in occasioning 
the condition known as asthenopia, but in the causation of 
many other important nervous disturbances. 
If this statement is admitted, it will be evident that the 
subject of irregularities in the actions of the ocular muscles 
must assume a greater importance than when disturbances 
of equilibrium were regarded as only occasional factors of 
asthenopia, and when these disturbances were looked for 
mainly in a single direction, in case they were not entirely 
disregarded. It is true, even at the present time, that “ in- 
sufficiency of the intend ” is the only disturbance of the 
ocular muscles, excluding strabismus or some of the results 
of paralysis, mentioned in the majority of the text-books 
upon the eye. Indeed, the importance of even this defect 
is hardly dwelt upon at any considerable length in many of 
these works, and it is not at all uncommon for the oculist to 
overlook the condition in his practical work. 
Defects which result in lasting difficulties and perplexi- 
ties in the performance of binocular vision are not to be 2 
A SYSTEM OF TERMS 
ignored; and the rdle of the ocular muscles in the causation 
of many nervous disturbances is undoubtedly of very con- 
siderable importance. 
As the investigator in this department of ophthalmology 
proceeds in his researches, or attempts to record bis obser- 
vations, he is met by the fact that the terms now in use are 
not only frequently inaccurate and misleading, but wholly 
inadequate to describe many of the states observed. 
To illustrate the two factors of the proposition just made, 
a few ordinary conditions may be adduced: 
1. The expressions employed to designate the deviations 
from the state of physiological equilibrium are often incor- 
rect and misleading. 
The term “ insufficiency of the interni ” is used to ex- 
press a state of the muscles of the eyes which is shown by 
the equilibrium test of Graefe at reading distance. In this 
test the images seen by the two eyes are separated by a 
prism held vertically, with its base exactly up or down be- 
fore one of the eyes. If, under these circumstances, the 
images deviate laterally in directions opposite to the two 
eyes—that is, if the image of the right eye deviates to the 
left, and of the left eye to the right—there is said to be 
“ insufficiency of the interni ” of as many degrees as equals 
the strength of a prism which, with its base toward the nose, 
will bring the two images in a vertical line. The expression 
“ insufficiency of the interni ” in this relation is used to in- 
dicate the fact that the internal recti muscles are “ insuffi- 
cient ” to counterbalance the external recti; and it also car- 
ries the idea that the externi are, in proportion to their 
physiological state, stronger than the interni, or that the 
interni are, proportionally to the others, abnormally weak ; 
tending thereby to balance the eyes outward, so as to cause 
an unusual and excessive demand upon the internal recti in 
close work. RELATING TO “INSUFFICIENCIES.” 
3 
The fact that a great many cases, in which the equili- 
brium test of Graefe shows the conditions described, are 
really “insufficiency of the externi”and not of the interni, 
must occur to any careful observer. Such a one will often 
find that, if he makes his test of equilibrium while the 
ocular muscles are in a comparative state of repose, as when 
looking at an object at a distance of six metres or more, he 
may find very marked “ insufficiency of the externi.” He 
may even observe that, if a screen is passed before one of 
the eyes while the other continues its gaze at the distant ob- 
ject, the covered eye will deviate in a marked manner in- 
ward. If the screen is quickly changed to the opposite eye, 
he will see the lately covered eye move outward in order to 
fix the object. He may make various other tests which will 
demonstrate beyond a doubt that the real balance of the 
eyes is inward, and yet, when he makes the test of the dot 
and line of Graefe, or any similar test, at near point, lie has 
marked “ insufficiency <>f the interni.” 
It is manifestly incorrect to say of such a muscular 
arrangement that the interni are “ insufficient,” and espe- 
cially when by such a term it is generally understood that 
the outer are the stronger of the two opposing sets of mus- 
cles. 
Again, in certain cases of what is known as “ insuffi- 
ciency of the interni,” one of the eyes actually deviates 
inward while the other deviates outward, while in a still 
greater number an apparent “ insufficiency of the inter- 
ni ” results from irregularities in the superior or inferior 
recti. 
Many other illustrations of the truth that this term as 
employed is misleading might be cited, but, without further 
expenditure of time or space, we may pass to the other fac- 
tor of the proposition. 
2. The term “ insufficiency ” is quite inadequate to ex- 4 
A SYSTEM OF TERMS 
press the conditions of deviation from the equilibrium as 
they may be observed. 
Graefe, as one of the great pioneers in modern ophthal- 
mology, and as the greatest authority on the subject of 
muscular asthenopia, recognized some of these deviations, 
and not only regarded “ insufficiency of the interni ” as a 
condition of notable importance, but wrote also of “ insuffi- 
ciency of the extend.” 
Notwithstanding his remarkable observations, much re- 
mained to be learned in this department of ophthalmology. 
While Graefe's great authority is to be fully recognized, 
the knowledge of these important conditions may yet be 
greatly extended. 
A class of deviations not at all uncommon, and one 
which induces great nervous perplexity, is that in which the 
tendency is for the visual line of one eye to deviate above 
that of the other. 
In examining some thousands of cases of “ insufficien- 
cies ” I have found a very important proportion of such 
tendencies. There is no term now in use which definitely 
expresses this condition. We can not say that it is insuffi- 
ciency of one or other superior or inferior rectus, for it is, 
in the great majority of cases, impossible to determine 
through what special influence the equilibrium is lost. We 
have not here, as in paralysis of the muscles, the definite 
guides of restricted motions by which we may determine 
the exact location of the trouble. Indeed, the defect may 
include an inclination on the part of the one eye to deviate 
upward, and on the part of the other to deviate downward. 
We might, perhaps, call such a condition “ insufficiency in 
a vertical direction,” with the right (or left) line of vision 
inclined to deviate upward. 
This would be a descriptive and somewhat extended ex- 
pression. It would still be inaccurate, for it implies a weak- RELATING TO “INSUFFICIENCIES.” 
5 
ness of some muscle, when the actual state maybe an excess 
of tension on the part of some other muscle. 
Again, there may and often does exist a combination of 
faulty tendencies in more than one direction. The eyes may 
incline to deviate in both the vertical and the horizontal 
planes, the result of which will be a tending of the visual 
lines to deviate in an oblique manner. It must be apparent 
that the term “ insufficiency ” is inadequate to express all 
these tendencies. 
There may be some propriety in using the expression 
“ insufficiency of the interni ” in many cases, but in these 
just cited it would be impossible for us to speak of insuffi- 
ciency of this or that oblique muscle without more accurate 
information than we are likely to possess. Indeed, in the 
majority of cases these muscles may not be influential factors 
in the condition described. 
Some term better adapted to express just what is in- 
tended, and nothing more, is needed. It is after much hesi- 
tation and doubt whether a suggestion involving the use of 
new terms in connection with a subject which has already 
engaged the attention of many able investigators might not 
be regarded as needless and presumptuous, that I have ven- 
tured to propose such an innovation. If, however, a change 
is to be made at any time in the classification and nomen- 
clature of these defects, such change should be made before 
the literature becomes still more extended. 
The first need in a scientific classification of these 
muscular defects is the possession of such terms as, with 
proper modifications, shall justly express the conditions 
described. 
The terms which have already been employed are all un- 
satisfactory, and are not uniformly employed by different wri- 
ters to describe precisely similar conditions. No terms now 
in common use occur to me as being in all respects desirable, 6 
A SYSTEM OF TERMS 
We may, therefore, select some word which shall con- 
vey the general idea and which, with its proper modifica- 
tions, will express our meaning with specific variations. 
Such a term should not, like the word “ insufficiency,” at- 
tempt to describe the exact nature of the muscular condi- 
tions, for this is often, if not generally, a subject of uncer- 
tainty. It should rather indicate the resultant facts as shown 
by the tendency of the visual lines to deviate from the physio- 
logical equilibrium. Nor should the term convey the idea 
of an actual turning, or deviation of one of the visual lines 
from what should be the common point of fixation. It 
should express a tendency to such deviation of such charac- 
ter that, should the force of the will be removed, this actual 
turning would result. 
The visual lines, in the conditions under consideration, 
are held in such relations to each other as to permit of more 
or less perfect binocular vision, but at an expense of a cer- 
tain excess of nervous effort. In this we have the distinc- 
tion between these conditions and those known as strabis- 
mus ; for, while in these there is habitual binocular vision, 
in strabismus there is habitual diplopia, either conscious or 
unconscious. It is true that a fusion of images is possible 
in many cases of strabismus, and that slight diplopia may be- 
come to a certain degree a habit, in the conditions under 
consideration. Nevertheless, a condition of habitual di- 
plopia should in general be regarded as distinguishing stra- 
bismus from these conditions. 
The Greek word $dpos (a tending) seems to fulfill the 
conditions required, and accurately expresses our meaning 
in regard to this class of defects. With this for our central 
idea we may easily express every variety of tendency to de- 
viation, as well as the absence of such tendency. Thus the 
two generic terms orthophoria (dp0os, right, </>opos, a tend- 
ing) and heterophoria (erepos, different) would express re- RELATING TO “INSUFFICIENCIES.” 
7 
spectively a tendency straight forward and a tendency in 
some other direction. 
In order that these terms should possess precise signifi- 
cation, the relation of the visual lines to which they are ap- 
plied should be determined under the uniform conditions 
which are here given. 
The eves should be directed toward an object situated 
at a given distance from them, and the head should be in the 
position known as the “ natural ” or “ primary ” position. The 
most convenient distance for the object is that at which tests 
for refraction are commonly made; that is, twenty feet, or six 
metres. This distance is, therefore, chosen as the standard 
for the determination of orthophoria and heterophoria. The 
best object for use in these determinations is a lighted candle 
against a dark background. It should be on a level with 
the eyes and at a distance of twenty feet. If ametropia ex- 
ists, the eyes should be supplied with suitable correcting 
glasses. In the “ natural position ” the body and head are 
erect, the eyes are in the same horizontal plane, and the 
median line (a horizontal line at right angles with the line 
connecting the two eyes) is directed exactly toward the 
object. Under these circumstances there should be in 
orthophoria the minimum of muscular innervation. 
These conditions being observed, we may ascertain the 
existence of muscular equilibrium or its absence by means 
of prisms in the manner familiar to all oculists. 
The determination of the muscular conditions at near 
points will occupy our attention as we proceed. It is to be 
remembered that the results in such examinations are by no 
means absolute. Heterophoria may, like hypermetropia, be 
partly or entirely latent. Indeed, as in actual hypermetropia 
we sometimes have apparent myopia, so with an actual in- 
ward tendency an apparent outward tendency may be ob- 
served. 8 
A SYSTEM OF TERMS 
The different relations of the visual lines which may he 
now found may he defined and arranged as follow?*, a state 
of the most complete relaxation of muscular effort attainable 
being always supposed : 
I. Generic Terms.— Orthophoria: A tending of the visu- 
al lines in parallelism. Heterophoria: A tending of these 
lines in some other way. 
II. Specific Terms. — Heterophoria may be divided 
into: 
1. Esophoria: A tending of the visual lines inward. 
2. Exophoria: A tending of the lines outward. 
3. Hyperphoria (right or left) : A tending of the right 
or left visual line in a direction above its fellow. 
This term does not imply that the line to which it is re- 
ferred is too high, but that it is higher than the other, with- 
out indicating which may be at fault. 
III. Compound Terms.—Tendencies in oblique direc- 
tions may be expressed as hyperesophoria, a tending up- 
ward and inward ; or hyperexophoria, a tending upward and 
outward. The designation “right” or “left” must be ap- 
plied to these terms. 
In recording the respective elements of such compound 
expressions I have employed the sign l_ . For example, if 
it is desired to indicate that the right visual line tends 
above its fellow 3°, and that there is a tending inward of 
4°, the facts are noted thus: Right hyperesophoria, 3° 
L_ 4°. 
In the absence of any means of producing a uniform 
state of relaxation of the long ocular muscles, such as we 
possess in atropine for the ciliary muscles, we must resort 
to every known device to ascertain as nearly as possible 
the true relations of the muscles. Methods other than 
that of measuring the deviation when diplopia is produced 
should, however, be regarded as auxiliary, and the record RELATING TO “INSUFFICIENCIES.” 
9 
of ortho- or heterophoria should be made from the diplopia 
test. 
The powers of the different pairs of muscles to over- 
come prisms should next be determined. Some confusion 
has existed in the use of terms to express this power. Thus, 
the words adduction and abduction have been employed by 
Graefe and succeeding writers to express the power of the 
eyes to overcome respectively a prism with its base out or 
in. They have, however, been employed to express this 
power both when the object of fixation has been at a con- 
siderable distance and when at the ordinary reading dis- 
tance. 
The same words are also used to express the limits of ex- 
cursion of the eyes outward or inward in the act of fixation. 
The words convergence and divergence have similarly 
been employed to express different classes of phenomena. 
As the words abduction and adduction are necessary to ex- 
press the power of moving outward and inward of either eye 
singly, and as the terms convergence and divergence must 
in all cases imply the approach or the separation of the axes 
of the two eyes, whether in the act of overcoming a prism 
or otherwise, there might be an advantage in employing the 
word convergence to indicate the highest degree of power of 
blending images at a distance of twenty feet when a prism 
with its base out is interposed ; and the term divergence to 
indicate the limit of power to overcome a prism with its 
base in. This latter would also be less liable to objection 
for the reason that, while each eye is habitually directed in 
abduction and adduction, the two are rarely by voluntary 
effort caused to diverge except by the influence of a prism. 
The fact, however, that Graefe in his classic treatise on 
muscular asthenopia employed the words abduction and 
adduction to indicate the ability to overcome prisms must, 
beyond a doubt, determine the point, and these words 10 
A SYSTEM OF TERMS 
should, therefore, represent the diverging and converging 
power with prisms. The standard of distance should, how- 
ever, be uniform with that for the test for ortho- and hete- 
rophoria. 
It often happens that images can be united when a 
prism is placed before an eye with its base up or down, but 
that diplopia is produced if the prism is reversed, or if it is 
placed in the first position before the other eye. In other 
words, the tendency of one visual line being higher than 
the other, the power to blend images is greater when the 
prism is placed in one than when placed in the opposite 
direction. 
This condition is one of great importance, and no exami- 
nation of muscular equilibrium should be regarded as com- 
plete in which its presence or absence is not determined. 
The ability to overcome a prism with its base down may be 
called sursurnduction, and the eye before which the prism 
is placed is indicated by the word “ right ” or “ left.” 
It remains to consider the relations of the muscles when 
the eves are directed to objects at the usual reading dis- 
tance. 
These relations may be uniform with those manifested 
at a distance, or they may vary in degree or in the direction 
of greatest apparent energy. To these conditions it might 
at first appear best to apply the familiar terms “insuffi- 
ciency of the interni ” or “ externi.” 
The objections are that the terms have already been em- 
ployed to express the relations of the eyes in accommoda- 
tion and also in repose, and that only two of many condi- 
tions can he described. 
The relations of the visual lines in accommodation do 
not always depend upon the comparative strength or weak- 
ness of the opposing muscles, but upon a peculiar state of 
innervation of the muscles. RELATING TO “INSUFFICIENCIES.” 
11 
The habit of maintaining an excessive tension upon tlie 
outer muscles in order to overcome esophoria frequently 
manifests itself in the near test as “ insufficiency of the in- 
terni.” 
These considerations render it desirable that a unifor- 
mity in the descriptive terms for the near and distant tests 
should be maintained. The terms already employed for 
distance may, therefore, be properly used if the modifying 
phrase “ in accommodation ” is added. Thus we should 
have for insufficiency of the interni exophoria in accommo- 
dation, etc. 
The relations of the ocular muscles should, as Graefe 
has shown, occupy a prominent place in the record of all 
examinations of the eyes for asthenopia or kindred troubles. 
if the system of words here introduced at first appears 
to be superfluous and therefore unnecessary, a careful con- 
sideration of the subject will be likely to convince a candid 
observer that new and more definite terms are needed to 
convey uniform meanings, and to express more conditions 
than are described by terms now in use. The terms here 
proposed are explicit in meaning, and the system, by ar- 
ranging the various deviating tendencies into classes, sug- 
gests to the examiner the conditions concerning which he 
should inform himself. REASONS WHY 
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