adults, for on the one hand it happens that gradually developed
monocular visual disturbances are only accidentally observed by patients
after they have reached a high degree, and it is very difficult then to
persuade these attentive observers that it is not a case of sudden
blindness of one eye. (Only a few people seem to be really aware that
they have two eyes, and still fewer appear to suspect the existence of a
visual field.)
In all these cases opportunity is hardly given for mistakes with
reference to the diagnosis of congenital amblyopia, as slowly developed
monocular defect scarcely occurs without ophthalmoscopic cause. On the
other hand, ophthalmoscopic symptoms (such as haemorrhage of the retinal
artery in the macula lutea) may disappear without leaving a trace, while
defective vision remains. The law of habit, however, usually helps us
here. In congenital monocular defect patients are generally accustomed
to this condition, and only notice it when special claim is made on the
visual faculty of this eye,--he, on the other hand, who is accustomed
to see with two equally good eyes, may not observe a gradually occurring
blindness of one eye, if his talent of observation be faulty, but I have
never had reason to suppose that a rapid depreciation of the central
visual acuteness of one eye is also overlooked. Rapidly occurring
monocular visual disturbances are noticed, whether detected with or
without the ophthalmoscope.
Two peculiarities appear in isolated cases of congenital amblyopia,
which may render the testing of vision difficult: rapid fatigue of the
retina, and depreciation of the central visual acuteness in such a way,
that an adjoining part of the retina possesses a better visual faculty
than the centre.
Rapid fatigue of the retina occurs in comparatively good visual
acuteness. For example:
CASE 16.--Mr. W--, aet. 35, came under treatment for conjunctivitis. In
testing the vision, emmetropia (or doubtful hypermetropia) was found on
the left, V. = 5/6. Refraction of right eye similar to that of left, V.
= 5/18 to 5/12, but with rapidly occurring fatigue of the retina.
Patient had observed this fifteen years before, when shooting during his
period of army service. Position and movements of the eyes are normal.
This peculiarity occurs more often in higher degrees of defective
vision. For example:
CASE 17.--Mrs. von G--, aet. 60, has always seen badly with the left eye.
On the right H. 1.25 D., V. 5/12. On the left with + 2 D., V. 1/12 with
+ 5 D. words of No. 1.75 were recognised; but the visual acuteness above
stated is only present at the first moment; after a few seconds
everything disappears in a fog. The left eye has a slightly conical
nebulous cornea, detected only on focal illumination, which does not,
however, cause the slightest irregular astigmatism, and cannot,
therefore, serve as explanation of the defective sight.
This rapid fatigue, which only permits the visual acuity present to be
estimated for a short period at a time, may easily result in the visual
acuity being supposed to be worse than it is.
The other phenomenon above mentioned, which occurs in defective vision
without being actually a necessary symptom, is the depreciation of the
central visual acuity, which we designate as central scotoma in acquired
amblyopia. It should be remembered that the visual acuteness which we
determine under these conditions is something different from what we are
usually accustomed to designate by this idea. When we simply talk of
visual acuity we always imply the central visual acuity; however, in
cases where the centre of the retina is so injured in its function, that
the peripheral parts lying near are too often called into requisition,
we do not determine the central visual acuity at all, but that of the
nearest and at the same time best, excentric part. We cannot prevent
patients from using that part of the retina which seems best to them for
recognising the test objects. In such cases (just as in acquired central
scotoma) continuous print is read badly, and with more trouble than one
would expect from the visual acuteness which is specified in the
recognition of single letters. Of course spelling and reading are two
different things; the excentric visual acuity may perfectly suffice for
the recognition of single letters, central and also excentric visual
acuity is necessary for reading. There are patients who, despite full
visual acuteness, are unable to read continuously, as soon as a defect
in the right half of the visual field extends close to the fixation
point. To read fluently, the excentric vision must work on in advance
for the width of several letters, but if the first letter is seen
excentrically, the excentric visual acuteness rapidly sinking in a
physiological way, does not suffice for the following ones.
When testing the vision these circumstances should be carefully
regarded. The apparent contradiction between the visual acuteness
specified with test-letters, and the uncertainty in reading continuous
print, may be taken for simulation (I have seen some sad examples of
this in acquired central scotoma), and, on the other hand, if in the
form of defective vision now under discussion we content ourselves by
merely employing reading tests, we take the visual acuteness to be worse
than it is, or than we find it later when single test-letters are used,
for even though excentric, it is yet always visual acuteness. The
excentricity of that part of the retina put into fixation is usually so
slight, that the oblique direction of the visual axis cannot be seen
with the naked eye; if considerable and extensive defect of the centre
of the retina is present, either varying fixation occurs, sometimes
parts lying to the nasal and sometimes to the temporal side are put into
fixation; or excentric fixation exists; an inner retinal area but
sometimes also a temporal then usually has comparatively the best visual
acuteness.
A third peculiarity which sometimes occurs in extreme degrees of
congenital amblyopia, is monocular nystagmus of the weak eye. This
trembling may be so slight that it is only observable during
investigation with the ophthalmoscope; in other cases it is most marked
as soon as the weak eye is put into fixation by exclusion of the sound
one.
Cases of congenital amblyopia in both eyes, where no explanatory cause
can be traced, and no nystagmus is present, are rare, but all the more
interesting. For instance:
CASE 18.--Mr. F--, aet. 56, has seen badly from childhood; the visual
acuteness of each eye singly examined amounts to 1/18 to 1/12, binocular
1/12. No. 0.75 is read with difficulty at 8 cm. Ophthalmoscopic
condition is normal. In mydriasis by atropine hypermetropia of 3 to 4
dioptres results. With convex 3. 5 D. on the right V. 1/18 to 1/12, on
the left V. 1/12, binocular V. 1/12 to 1/9, with convex 6 D. still only
0.75 can be read, but more fluently than with the naked eyes.
Normal binocular fusion may continue to exist even in extreme degrees of
monocular weak sight; I have observed it up to a visual acuteness of
1/24. The stereoscope is well adapted to prove binocular fusion in these
cases; only we must then take care that sufficiently large letters are
present in the visual field of the defective eye, so that they may
easily be recognised with the existing visual acuteness. Binocular
fusion is naturally rendered still more difficult if the weak-sighted
eye is at the same time hypermetropic to a high degree, as it then
receives simultaneously indistinct retinal images on account of the
difference of refraction; and yet in the above table there are 117 cases
with hypermetropia of at least 2 D. in the better eye, and faulty visual
acuteness in the other, 7 with visual acuteness of less than 1/7 to V.
1/12, and 9 with less than 1/12 to V. 1/36.
In the highest degrees of congenital defective vision, binocular fusion
cannot as a rule be proved; partly because the methods of investigation
by which we are able to prove binocular fusion presuppose the existence
of a sufficient visual acuteness. On the other hand, it cannot be
expected that normal binocular vision can be learnt with such a large
amount of monocular defective vision. If the relative strength of the
muscles is normal, so also are the position and movements of the eyes,
if elastic preponderance on the part of the muscles is present, which in
monocular defective vision of considerable degree is no longer governed
by binocular fusion, and this is frequently the case, squint is
developed.
Sometimes other congenital anomalies are present at the same time with
congenital defective vision (for example, congenital dermoid growths on
the edge of the cornea), and undoubtedly hereditary influences play a
considerable role therein.
In order to determine the relation of congenital defective vision
without squint, to defective vision with squint, I have taken those
cases where congenital defective vision without squint was observed,
together with the cases of squint, from the diaries of my private
practice for the last ten years. I have personally investigated every
case, and the observations on each were carefully examined before being
included in the statistics; all cases with myopia of six or more
dioptres, all cases of double nystagmus, and, finally, all those cases
where the previous existence of squint might be suspected, were
excluded, as above stated. I must also remark that before the last ten
years I had not begun to collect these cases. In order to find monocular
congenital defective vision one must seek for it, as patients usually
come under treatment for quite different disorders, and in the
consulting-room there is not always time carefully to investigate what
possesses interest for us but none for the patient. In cases of squint
the opportunity for investigating the power of vision does not escape us
so easily, and yet the same list, which contains among 629 patients 177
cases of squint with a visual acuteness of 1/8 to less than 1/36,
furnished at the same time 98 cases with undoubted congenital defective
vision of the same high degree without squint, which I place together in
the following review.
Cases of congenital amblyopia with visual acuteness of 1/7 are so
frequent, that I have not drawn up special statistics of them. I was not
anxious to collect a large number of cases but only material for
evidence. I have therefore divided the 98 cases I observed into 3
groups. (1) Cases with visual acuteness of less than 1/7 to V. 1/12; (2)
V. less than 1/12 to V. 1/36; (3) visual acuteness less than 1/36. The
limits between these groups are of course not very sharply defined, for
what is designated as "measurement" of visual acuteness contains, even
if we accept the statements of patients as trustworthy, not an
inconsiderable number of sources of error; and we often find a
remarkable absence of conformity in the analysed causes of congenital
amblyopia, according as we seek to determine the visual acuteness by
means of single test-letters or by reading printed matter. In a case of
visual acuteness of 1/12 No. 0.75 with convex 6 was the smallest type
that could be read, and that with difficulty, larger type was usually
required; and in one case where at first only single words of No. 2.25
were read with difficulty--this test was on that account repeated in
myosis by eserine--No. 1.75 was finally the smallest print which could
with the same difficulty be deciphered. In the division of the groups
here arranged the best visual acuteness ascertained in the various
examinations was always used as the basis.
A. Vision less than 1/7 to V. 1/12 38 cases. The examination of the
better eye showed:
(_a_) Emmetropia in 18 cases. A determination of refraction,
mostly ophthalmoscopic, of the weaker eye is submitted in 11
cases, which divide themselves into, 4 with emmetropia, 3
with hypermetropia (of H. 2 D. and 2.25 D.), 3 with
hypermetropic astigmatism, I with myopic astigmatism.
(_b_) Myopia in 5 cases (3 of M. 1 D. to 1.5 D., 2 of M. 4.5
D. and 4 D.), the condition of the defective eye was
determined in 3 cases, and was twice hypermetropic, once
astigmatic.
(_c_) Hypermetropia in 8 cases, hypermetropic astigmatism in
3. In 4 cases an exact determination of refraction even of
the better eye was for some reason impracticable.
There are 4 cases in this group where the visual acuteness in both eyes
did not exceed the above-stated small amount, and one which was
interesting from another point of view.
CASE 19.--Max L--, aet. 8-1/2, recognises No. 24, and a few letters of 18
at 5 metres with the better eye with convex 6 D.; at 1 metre V. 1/4 to
1/3, the left eye recognises only No. 60 at 5 m. with + 6 D. at 1 m. No.
0.75 is read with difficulty. If we exclude one eye it lapses into now
less, now greater convergence, and still no squint is present, but
diplopia as well as binocular fusion can be proved by the aid of prisms.
The theory of Donders that squint is less frequent in hypermetropia of
high degree because too strong convergence would not suffice to furnish
clear retinal images, is scarcely tenable in the face of such cases. If
indistinct retinal images are added to a visual acuteness of only 1/3 to
1/4 still, even with faulty accommodation, it is difficult to believe
how a child could learn to read if it did not hold the book close to its
eyes, which was not the case here, and indeed seldom happens. Therefore,
in spite of defective vision the accommodation must have sufficed,
without sacrificing binocular fusion, whilst in all probability
accommodative convergence followed on exclusion of one eye.
B. 48 cases had visual acuteness from 1/12 to 1/36. The better eye was--
(_a_) Emmetropic in 16 cases; in 6 of them the refraction of
the defective eye was determined, which showed in one case
emmetropia, 3 hypermetropia, 2 astigmatism.
(_b_) Myopia of the better eye was present in 7 cases (in 3
myopia of 1 D., in 4 M. 3 D. to 6 D.).
(_c_) Hypermetropia in 18, astigmatism in 4 cases. In 3
cases the condition of the better eye was, for some reason
or other, indeterminable.
In this group I should like to point out the following cases as worthy
of attention:
CASE 20.--Margarethe T--, aet. 16, has hypermetropia 2 D. in the right
eye, V. 5/6, in the left the ophthalmoscope shows with an otherwise
normal condition a higher degree of hypermetropia, with + 6.5 D., V.
1/18, with + 10 D. No. 3.0 is read. No spectacles have been used until
now; for the past few years school tasks have been performed with a
certain effort, only during the last year the asthenopia has increased.
Squint is not present, and with prisms as well as with the stereoscope
(by the use of objects, whose size corresponds to the defective sight on
the left side) binocular fusion can be proved.
The case is the same as regards divergent strabismus.
CASE 21.--Mr. H--, aet. 28, has myopia 6 D., V. 6/9 in the right eye; the
left eye has always been weak sighted, emmetropia is detected with the
ophthalmoscope, with normal fundus, V. 1/18. No squint, binocular fusion
can be proved with prisms.
CASE 22.--Mr. B--, aet. 47, has hypermetropia 5 D., V. 5/9 in the right
eye. Left eye with + 5 D., V. 1/18 (a few letters of 12 also were
recognised at 1 m.). It seems, however, that the patient is not able
exactly to indicate the position of the retinal images of his left eye,
he does not know, as he expresses himself, "whether the letters stand
here or there." Patient observed the defective sight long ago; the
ophthalmoscopic condition is normal. Patient really comes on account of
his son, aged 7-1/2, in whom hypermetropia of 3.5 dioptres is detected
with the ophthalmoscope, right eye with + 3.5 V. 5/9. Left eye has
convergent squint, V. 1/36, No. 3.0 is read with + 6.5 D.
The hereditary tendency is seen also in the following case:
CASE 23.--Mrs. S--, aet. about 46, on the left H. 4 D., V. 5/18 to 5/12,
has used no spectacles until now, and reads No. 0.75 without glasses at
about 15 cm. R. with + 4 D., V. 1/18, with + 6.5 D. large letters of No.
5.0 are recognised.
Two sons, present at the same time, are hypermetropic. One has in either
eye V. 1/4, the other a slighter degree of congenital amblyopia.
CASE 24.--Johanna L--, aet. 4, came under treatment for a congenital
fibroma covered with hair, about the size of a cherry-stone, situated on
the outer corneal margin of the left eye, which was removed. Three years
later, when the child had learnt to read, emmetropia and full visual
acuteness was observed in the right eye, with the left No. 4.0 only is
read with difficulty. The ophthalmoscope shows a slight degree of
irregular astigmatism of the cornea, which in no way explains the
defective vision; the image of the fundus is perfectly clear and quite
normal.
CASE 25 afforded me a not altogether pleasant surprise. Martin M--, aet.
58, has matured cataract in the right eye, with perfectly satisfactory
light reflex, proper projection, &c. On the left progressive cloudiness
of the lens has begun. The course of operation and cure were regular in
every respect, but the power of vision finally was so small that with a
clear pupillary area, and otherwise normal condition, only single words
of No. 3.0 were recognised with difficulty at 10 to 15 cm. with convex
20 D. For the first time the patient remembers that he noticed the
defective sight in his right eye at the age of sixteen, and was for this
exempt from army service. The operation performed later on the left eye
procured satisfactory vision.
C. Visual acuteness of less than 1/36 12 cases.
Determination of refraction of the better eye is given in 6 cases, and
showed twice emmetropia, twice slight myopia, twice hypermetropia. I
only possess an exact ophthalmoscopic determination of the condition of
the defective-sighted eye in one instance with H. 2.5 D.
This group is of special interest in that it represents the extreme
degrees of congenital amblyopia, and, on the other hand, because it
contains 5 cases of children under 10 years of age.
CASE 26.--Constanze von M--, aet. 9-1/2. Defective vision on the left
side had been noticed long before by the child's parents. On May 1,
1879, emmetropia was observed in right eye, V. 5/12 to 5/9. No. 0.4 is
read at 15 cm. On the left, only movements of the hand are seen, fingers
cannot be counted even when close to the eye; the visual field is good,
that is, on moving the hand in the periphery of the visual field the
child sees "something" without being able to state what it is. Reaction
of the pupils as rapid and equal as usual. The ophthalmoscopic condition
(even with dilated pupils) is perfectly normal. All tests for simulation
were of course applied.
On account of the importance of the case, I suggested another
examination a year and a half later, on the 22nd December, 1880, which
showed precisely the same result as the former one--optic disc, macula
lutea, &c., perfectly normal, the ophthalmoscopic determination of the
refraction shows H. 2.5 D.
The child's father also possesses in the left eye a slight degree of
congenital defective sight, observed for many years, with normal
ophthalmoscopic condition; No. 0.5 is read with + 6.5 D. at 10 cm.
CASE 27.--Tina S--, aet. 6. The defective sight of the left eye had been
remarked some months previously; report on July 16th, 1878: R. full
visual acuteness, L. movements of the hand are scarcely visible. The
child cannot count fingers. Normal ophthalmoscopic condition. Eserine
and separate use were prescribed. On September 9th, 1878, fingers were
counted with the left eye at 1.5 m., single words of No. 4.0 were
recognised, No. 3.5 with convex 6.5 D., but always with oscillating
fixation. The improvement in the child's statements may be referred to
the fact that she had meanwhile learnt to form right conclusions from
the very imperfect sensual impressions of her left eye.
CASE 28.--Frank J--, aet. 10. Left eye. V. 10/50 to 10/40, No. 1-1/2
Snellen is read at 4 inches. On the right, nystagmus on fixation,
fingers are counted at 5-6 feet. The ophthalmoscopic condition is
normal. A sister of the boy squints.
CASE 29.--Ernest G--, aet. 8, has slight nebulae on both corneae. On the
left V. 15/40. On the right, fingers are counted at 4 inches with visual
axis deviating inwards.
CASE 30.--I operated on Moritz L-- for congenital cataract before he was
a year old in 1869 by means of a needle operation. In June, 1877, a thin
ophthalmoscopically transparent secondary cataract appeared in both
eyes; on the left, with convex 12 D. V. 3/24 to 3/18, with convex 16 D.
No. 0.4 is read at 10 cm. On the right, with convex 12 D., fingers are
counted with difficulty at about 1 m., with inward deviation of visual
axis.
CASE 31 is also worthy of note. Carl H--, aet. 22, shows quite a number
of congenital anomalies on the left side of the face, harelip, deformed
nostril and a skin defect on the inner corner of the eyelid. There is a
congenital dermoid growth of the size of half a pea situated on the
inner lower corneal margin. A slight irregularity in the curve of the
cornea near the dermoid is detected with the ophthalmoscope; the fundus
of the eye is perfectly normal. Fingers are not counted further off than
a metre with visual axis deviating inwards. The right eye is emmetropic
(perhaps slightly hypermetropic), and has full visual acuteness. There
is no squint.
It is customary to "explain" these cases of monocular amblyopia by
previously existing squint, and one is quite satisfied if by the
examination of patients it is only possible to prove that they have
occasionally squinted, although the advocates of the amblyopia ex
anopsia disallow the presence of the same under these conditions, that
is, in periodic squint. Of course a theory which cannot exist without
the assertion that occasional alternation suffices to hinder the
development of defective vision caused by disuse, cannot possibly hold
periodic squint to be the cause of it. Certainly permanent squint may
also disappear, but this much I have been able to determine, that this
seldom happens before the twelfth year of life, and one may surely
reckon that children in whom permanent squint is developed at the usual
early period of life, still squint at the age of ten years. Cases 24 and
26 to 30 can under no circumstances be explained by previous squint,
notwithstanding that they represent the extremest degrees of amblyopia,
but the question is undoubtedly that of congenital defective vision;
moreover I have excluded from the statistics of congenital amblyopia all
cases in which the previous presence of squint could even be supposed.
A table of the cases above described with reference to the defective
condition is interesting; when a determination of refraction existed for
the weak eye I have given it, and when this was not the case I have
stated that of the better eye, thus it is seen that among 85 cases in
which the refraction was determined, hypermetropia (including
hypermetropic astigmatism) was present in 39. Hypermetropia was found
then in 47 per cent of all the cases. The percentage would probably be
higher, if all weak-sighted eyes had been examined from the beginning as
to their state of refraction, but as I only learnt to know the relation
between hypermetropia and the higher degrees of congenital amblyopia
from my statistics, I did not take notice of this relation when
investigating individual cases.
How does congenital amblyopia now stand in relation to that disturbance
of vision which we observe in squint? I see no difference; whether
squint is present or not, the form of defective vision is precisely the
same, and nothing happens in the combination with squint which could not
also be proved without it. The relation to hypermetropia, which is
proved with congenital amblyopia, also appears in squint.
A collective table of cases of convergent and divergent squint included
in the statistics (pp. 19 and 47) shows: