Extracted from the 
TRANSACTIONS OF THE COLLEGE OF PHYSICIANS OF 
PHILADELPHIA. 
THIRD SERIES. VOLUME III. HEMIOPIA AND DECUSSATION IN THE OPTIC 
CHIASM. 
GEORGE C. HAITIAN, M.D., 
SURGEON TO WILLS HOSPITAL, OPHTHALMIC AND AURAL SURGEON TO TIIE 
CHILDREN’S HOSPITAL. 
[Read July 4, 1877.] 
The theory of the semi-decussation of the fibres 
of the optic nerves in the chiasm, is often spoken of 
as Wollaston’s Theory. Wollaston is generally sup- 
posed to have been the first to suggest it, in 1824, to 
facilitate the explanation of a transient hemiopia oc- 
curring in his own case; but it is known that Sir 
Isaac Newton advocated the possibility of a semi- 
decussation in 1704. The name of Muller is also 
associated with this theory, and it has been adopted, 
without cpiestion, in nearly all the standard text-books 
on anatomy, physiology, and ophthalmic surgery. 
Within a few years, this long rest has been broken 
by the defection of a number of pathologists and phy- 
siologists, who have advocated the theory of total 
decussation, maintaining that all the fibres of each 
optic tract pass across to the eye of the opposite side. 
The weight of authority and the best of the argument 
are still on the side of the older theory, and Knapp 
(Archives of Ophthalmology and Otology, vol. i. No. 
2, p. 242,) in speaking of the experiments of Mor- 
gagni, Gudden, and Admiik, says, “ The results of 162 
HARLAN, 
these experiments are: in the clog and cat, if one eye 
or optic nerve is destroyed, the atrophy strikes Loth 
optic tracts, hut in the rabbit it strikes only the optic 
tract of the other side. The present phase of the 
question of the decussation is the following: In ani- 
mals that have no common field of vision, the cross- 
ing is total; in others that have a common field, the 
crossing is partial, corresponding to the extent of the 
common field. In man, there is half crossing.” As, 
however, the subject is still much discussed, it may 
be considered, to a certain extent, an open one; 
particularly when we find in so recent a publication 
as Mr. Carter’s Ophthalmic Surgery the statement 
that “It was recently believed that the decussation 
was only partial, and that the external fibres of each 
tract went to the same side; but this view is not 
supported by the later investigations.” 
In fish, the arrangement is simple and plain enough; 
the right nerve crosses entire above the left, and, if it 
may be considered as demonstrated by physiological 
experiments that in animals of higher development, 
and with a common field of vision, there is a partial 
decussation, the manner in which this twisting of 
the fibres has been brought about furnishes a curious 
problem for evolutionists. As has been pointed out by 
Wollaston, however, though the anatomical analogy 
has not been maintained, the physiological analogy is 
still complete ; for as, in the case of animals that have 
not a common field of vision, the axes of the eyes are 
directed outwards instead of forwards, the visual 
impression of objects on either side is conveyed to 
the opposite hemisphere of the brain, just as the HEMIOPIA. 
163 
semi-decussation theory supposes it to be in animals 
with a common field. 
There seem to be difficulties in the way of the 
microscopical study of the chiasm in man that pre- 
vent an agreement of authorities. Gudden insists 
that semi-decussation can he determined by a series of 
careful sections of the chiasm, while Mandlestamm 
and Michel claim that their anatomical researches 
demonstrate that the crossing is complete. This 
refers the question to clinical observation and patho- 
logical investigation, and may give an interest to the 
report of cases that bear upon it 
The terms right and left hemiopia, as they are now 
universally used, am rather unfortunate, and may 
lead to confusion in the minds of students, while even 
those more familiar with the subject may often have 
to hesitate for a moment to translate them from their 
real to their accepted meaning. This confusion of 
terms becomes more marked when we remember that 
the terms hemeralopia and nyctalopia are used in a 
different sense. By hemeralopia we express the fact 
that the patient can see in daytime but cannot see at 
night, that he is night-blind; while by right hemiopia, 
on the contrary, we mean that the patient cannot see 
on the right side but can see on the left. Naturally, 
therefore, the expression “ so-called'’ right or left 
hemiopia is sometimes met with. These terms can 
be made correct only by applying them to the retina 
instead of to the field of vision, for in right hemiopia 
the right side of the retina remains unaffected, and 
enables the patient to see to the left. By right hemi- 
opia, therefore, we really mean right half-blindness. 
The only entirely appropriate cases for the illustra- 164 
IIAKLAN, 
tion of theories of decussation are those in which 
there is a sharp line of demarcation, symmetrical on 
the two sides, between the deficient and the unaffected 
portions of the visual field, and in which there is no 
suspicion that the symptom may he due to disease of 
the retina or disk, or of the optic nerve in front of 
the chiasm. For example, a patient recently pre- 
sented himself at Wills Hospital with well-marked 
binocular hemiopia which at once suggested intra- 
cranial disease, but the ophthalmoscope showed an 
almost symmetrical retinal separation in each eye. 
This, of course, was a mere chance, but a chance not 
less likely to occur in the disk or in the anterior part 
of the nerve. Even in the chiasm, it seems hardly 
possible that any form of disease or of pressure from 
neighboring growths should accurately dissect out a 
certain set of fibres, leaving the others completely 
intact; so that a sharply defined, symmetrical, bin- 
ocular hemiopia may be considered as furnishing a 
very strong presumption, at least, in favor of lesion 
of the optic tract or of the brain behind it. 
The following two cases are fair illustrations of 
cerebral hemiopia. 
J. II., sight good until four weeks before examination, 
when it became obscured suddenly. Had had diabetes three 
or four years ago, but sugar had disappeared entirely from 
urine, and health seemed restored. Had lately had some 
headache, feeling of weight on top of head, and slight mental 
confusion and loss of memory; the right side of the field of 
vision was deficient, almost obliterated to the median line 
in each eye. In the left side he could read ordinary print 
with a slowness and difficulty that seemed to be due partly 
to imperfect vision, and partly to loss of memory and of the 
power of mental concentration. There was no other paraly- IIEMIOPIA. 
165 
sis. The ophthalmoscopic appearances were normal, except 
a slight engorgement of the retinal veins and several small 
yellowish-white spots in the neighborhood of each macula, 
suggesting albuminuria; albumen was found in the urine in 
considerable quantities. Eight months afterwards, the edge 
of the obscure portion of the field had receded, and was 
three inches to the right of the point of fixation, at a dis- 
tance of one foot from the eye. The line of demarcation 
was still sharp and vertical, and perfectly symmetrical in 
the two eyes, so that the same diagram accurately described 
the field in each. 
The ophthalmoscopic appearances in this case were 
barely sufficient to excite a suspicion of the earlier 
stages of albuminuric retinitis, which, as yet, inter- 
fered but little with vision. The right hemiopia 
pointed to a lesion of the left hemisphere of the brain, 
while the albuminuria indicated a condition of the 
vessels that would predispose to hemorrhagic extra- 
vasation, and the mental symptoms confirmed the 
diagnosis of cerebral disease. 
The second case has more interest, from the fact 
that it was complicated with other symptoms which 
located the disease almost positively on one side of 
the brain. 
Gf. II., set. 29, six months before liis admission to Wills 
Hospital had chancre, followed by eruption on the face, 
sore throat, and other unmistakable, secondary, syphilitic 
symptoms. About four months after the appearance of the 
chancre he had violent headache, which continued in less 
degree; but, three days before admission, he read for several 
hours with ease, before going to bed. The next morning 
he awoke with dizziness and dimness of sight. Double 
vision was first noticed two days afterwards. The following 
condition was found on examination. On the right side 166 
IIARLAN, 
there were partial ptosis, complete paralysis of internal rectus, 
paresis of superior and inferior recti, and sluggishness of 
the pupil. There was complete left hemiopia on both sides, 
with fair vision in the right halves of both fields. No 
other symptom in the left eye but diminution of visioti. 
0. D. Y. = U ? 0. S. Y. = 2I°. The ophthalmoscope showed 
only engorgement of the retinal veins, more marked in the 
right eye. On rough examination, there seemed to be a 
perfectly vertical and symmetrical line of demarcation 
through the macula; but when the fields were carefully 
taken, this line was found to incline a little from left to 
right for each eye, more decidedly for the left, and to he a 
little to the left of the macula on each side. After several 
wTeeks of treatment by mercurial inunction and large doses 
of iodide of potassium, the vision was much improved—0. D. 
and 0. S. Y. = but there was no change in the hemiopia. 
A gummy tumor or other lesion might easily involve both 
the optic tract and the third nerve in their passage over the 
crus cerebri, or the filaments of both at their origin, with- 
out implicating any other nerve; hut it is difficult to con- 
ceive how disease situated elsewhere than in the right side 
of the brain could produce this combination of symptoms. 
Medical literature furnishes numerous instances of 
hemiplegia with paralysis of the half of each retina on 
the side opposite to that of the limbs, and Dr. Hugh- 
liims Jackson considers it an almost invariable rule 
that when bilateral hemiopia is found in connection 
with hemiplegia, the patient cannot see to the para- 
lyzed side. 
It must be admitted, however, that, with a fair 
amount of ingenuity and a sufficiently strong bias, 
most of the phenomena of hemiopia can, on merely 
theoretical grounds, be explained by either theory of 
decussation. Thus, on the total decussation theory, 
right-sided hemiopia may be referred to pressure on HEMIOPIA. 
167 
the left external angle of the commissure involving 
the outer half of the left optic nerve and, at the same 
time, the outer half of the left optic tract, and, con- 
sequently, the inner half of the right optic nerve- 
fibres. 
Bitemporal hemiopia may be accounted for by 
pressure upon the anterior angle of the commissure, 
involving the inner halves of the optic nerves, and 
nasal hemiopia by pressure at the posterior angle 
involving the inner halves of the optic tracts, and, 
therefore, the outer halves of the optic nerve-fibres. 
On the semi-decussation theory, right- or left-sided 
hemiopia may be rationally explained by supposing a 
lesion of the optic tract of the opposite side, and 
binocular, temporal hemiopia may be referred either 
to pressure in front of the commissure involving the 
inner halves of the optic nerves, or, behind the com- 
missure, involving the inner halves of the optic tracts. 
Binocular, nasal hemiopia, cannot be explained by any 
single lesion, and this has been considered the weak 
point of the semi-decussation theory. The cases of 
this form of hemiopia are, however, so few, that, to 
say the least, they may be considered exceptional, 
and the existence of double lesions, nearly symmetri- 
cal, is almost within the range of possibility. Schoen, 
writing in 1874, says, “Nasal hemiopia is excessively 
rare, if ever met with. There is no record of an en- 
tirely incontestable case.” (Annales d’Oculistique, 
t. lxxii., p. 182.) I have not been able to find a de- 
tailed account of any case quite free from complica- 
tions. 
Some cases have been reported in which the lower 
half of both fields was absent, but I know of nothing 168 
HARLAN, 
to disprove Mauthner’s assertion that no well-de- 
scribed case with a sharply defined horizontal line is 
on record. Such a case might be explained, with about 
equal plausibility, on either theory. 
Though the theoretical discussions, which have 
been considerably extended on this subject, are often 
extremely ingenious and always interesting, any 
decision reached through them is, after all, merely an 
opinion, and no observations are positively conclusive 
that are not confirmed by post-mortem examination. 
I believe that wherever post-mortem evidence is 
entirely unequivocal, it will be found on the side of 
semi-decussation. 
When we remember the special prominence of 
nasal hemiopia in the discussion of this question, there 
seems a remarkable absence of this positive kind of 
evidence connected with it. The literature of liemi- 
opia furnishes only four cases of this form of the 
affection, in which post-mortem examinations have 
been made. Though, with perhaps one exception, 
none of these cases are free from local complications 
of disease of the retina, or of the nerve near the ball, 
or of both, which, on a rigid sifting, might fairly rule 
them out, a brief account of them may have, at least, 
some historical interest. 
The only one in which the ophthalmoscopic appearances 
are reported as normal, is recorded by Muller (quoted by 
Knapp, in Brown-Sequard’s Archives). The symptoms were 
complicated, and it was as much a case of temporal as of 
nasal hemiopia. There was first temporal, binocular hemi- 
opia, then total blindness, and then nasal hemiopia with 
well-defined lines. Post-mortem examination showed a 
tumor in the sella turcica as large as a medium-sized apple. hemiopia. 
169 
A second case is given by Schiile (quoted by Plenk, in Archives 
ot Ophthalmology and Otology, vol. v. No. 2, p. 201). “ The 
disease began with amblyopia in the right eye, atrophy of 
the papilla, with blue discoloration and marked reduction of 
eccentric vision ; later, atrophy commenced in the left papilla, 
with a similar course and changes in the arterial vessels. 
Autopsy: the ventricles much dilated; the infundibulum 
and both nerves distinctly atrophied and of a grayish color.” 
The same author also quotes a case observed by Wegner and 
Schmidt. The perceptive and non-perceptive portions of the 
visual fields were not divided by a sharply defined line. The 
ophthalmoscope showed neuro-retinitis. On post-mortem 
examination, a tumor was found in the median line of the 
brain, involving the infundibulum,fornix, and septum pellu- 
cidum. The microscope showed decided atrophic changes 
both in the nerves and retinae. The fourth case is reported 
by Knapp, in Prown-Sequard’s Archives. Vision was very 
much diminished throughout the whole field, the lines be- 
tween the totally and the partially obscured portions were 
not quite symmetrical in the two eyes, and there was optic 
neuritis in both. On post-mortem examination, the brain 
was found healthy, but the arteries at its base atheromatous. 
The nasal hemiopia was referred by Dr. Knapp to paralysis 
ot the outer halt of each retina, resulting from compression 
of the external fibres of both the nerve and optic tract, on 
both sides, by the anterior cerebral and posterior communi- 
cating arteries. It must be admitted that this ingenious 
arrangement has not seemed quite so clear to the opponents 
of semi-decussation. 
Binocular, temporal hemiopia, in which the inner 
halves of the retinae are involved, is also a very rare 
affection; and beside that of Muller, mentioned above, 
in which temporal hemiopia preceded the nasal, I can 
learn of only one post-mortem examination in such a 
case. It is reported by Samisch (Plenk, loc. cit.). 
In both ot these cases there were sarcomatous 170 
HARLAN, 
growths involving the anterior angle of the commis- 
sure, and the hemiopia, therefore, admits of equally 
satisfactory explanation on either theory. 
Autopsies in cases of homonymous bilateral hemiopia 
have been more numerous, and their results more 
definite. It is worthy of note that in all the reported 
cases the lesion has been behind the chiasm, and there- 
fore more strictly cerebral; these cases are in the 
nature of positive evidence, and, to my mind, are 
quite conclusive in favor of the semi-decussation 
theory. 
The first case of hemiopia on record is reported by 
Wollaston, who was himself the subject of it. After 
his death, an examination of the brain revealed a 
lesion of the right optic thalamus, which is described 
as converted into a tumor as large as a hen’s egg, 
harder than the brain, and somewhat of a caseous 
substance. (Mackenzie on the Eye, p. 931.) The 
connection of this tumor with the hemiopia, however, 
is far from clear, as the symptom, which occurred 
twice with an interval of twenty years, lasted only 
fifteen or twenty minutes each time, and the right 
halves of the retinae were involved on the first occa- 
sion and the left halves on the second. 
It seems more likely that this was one of those 
singular cases of transitory hemiopia, not very un- 
common, due to some temporary cause, and not 
dependent on discoverable organic change. 
The following post-mortem records, which are all 
that I have been able to find, are of quite recent date. 
Two are reported in the Archives of Ophthalmology and 
Otology, vol. v. No. 2, one by J. Hirschberg, of Berlin, and 
one by Dr. T. R. Pooley, of New York. In the firsf) there HEMIOPIA. 
171 
was “ defined, symmetrical, right-sided defect in the visual 
field of both eyes, with a nearly normal acuity of vision and 
a normal ophthalmoscopic picture, accompanied by aphasia and 
hemiplegia of the right side. The autopsy revealed a tumor 
as large as an apple in the left frontal lobe, implicating the 
left optic tract.” In Dr. Dooley’s case, there were right-sided 
hemiopia, sharply defined in the vertical meridian, partial 
hemiplegia of right side, and choked disk in the left eye, but 
no change of appearance in the right. On post-mortem 
examination, a gummy tumor was found in the left posterior 
lobe of the brain. The left thalamus opticus and the neigh- 
boring brain-substance were completely softened. A third 
case is also referred to in the same journal (Jackson, quoted 
by Plenk). There was bilateral, left hemiopia, and the 
autopsy showed pronounced softening of the right optic 
thalamus. 
In a case of left hemiplegia, left hemi-anresthesia, and left 
hemiopia, Dr. llughlings Jackson diagnosed disease of the 
right optic thalamus, and post-mortem examination showed 
softening confined to the posterior and inner part of the 
right optic thalamus. (-Medical Times and Gazette, Oct. 28, 
187G.) 
Dr. Gowers also reports a case in which there had been 
hemiopia tor several months before death, and in which post- 
mortem examination showed softening of the posterior 
tubercle of the optic thalamus on the opposite side. (Ibid.) 
A\ e may add to these, as approaching very nearly 
to an autopsy in the accuracy with which the lesion 
may he located, the case of gunshot injury of the 
l\ead reported by Drs. Keen and Thomson (Photo- 
graphic -Review of Medicine and Surgery, Feb. 1871). 
The wound of entrance was in the middle line, one 
and a quarter inches above the external occipital pro- 
tuberance, and the wound of exit two inches to the left 
ol the median line, and three inches above the wound 172 
HARLAN, 
of entrance. The patient was unconscious for several 
months, and had right hemiplegia for about a year. 
More than eight years after the injury, the field of 
vision was “found to be divided for each eye by a 
line passing through its centre, in the vertical direc- 
tion : total blindness existing to the right, and perfect 
vision to the left, of this line.” These cases need 
little comment; they are typical, uncomplicated in- 
stances of cerebral hemiopia, and their evidence is 
strong in favor of semi-decussation. 
There is another form of hemiopia which it may be 
of interest to mention in this connection, though not 
enough is known of it to give it any real scientific 
weight in the discussion. I refer to those strange 
cases of transient hemiopia which are met with most 
frequently in subjects of migraine, in whom they 
seem to be a kind of prodrome of the headache, 
though they occasionally ocdur without any other 
symptom. We not only know nothing of their eti- 
ology, but even the symptomatology, derived of neces- 
sity from the accounts of patients, is not definite or 
accurate. Usually, merely the fact that only the 
hal ves of objects are seen is reported, and we are 
without the means of knowing whether, in frequently 
recurring cases, the same side of the retina is always 
affected. In Wollaston’s case, opposite sides were 
affected in the two attacks, but the interval between 
them was so long that they can scarcely be considered 
as phenomena of the same disease. He relates the 
case of one of his friends, who had been habitually 
subject to this symptom for sixteen or seventeen 
years whenever his stomach was deranged, in whom 
the blindness was invariably in the right side. A 
medical gentleman who recently told me of his own HEMIOPIA. 
173 
case, assured me that the blindness was always on 
the same side, and that the line of demarcation was 
vertical and sharply defined. The symptom occurred 
quite frequently during his student-days, and was 
always the forerunner of a raging headache. 
Wecker (Maladies des Yeux, p. 384) speaks of 
recurrences of transient, bitemporal hemiopia, with 
sharp lines of demarcation, unaccompanied by cere- 
bral symptoms, and explains them by supposing an 
insufficient flow of blood, something like what is 
thought to occur in epilepsy, in certain regions of 
the brain supplied by symmetrical arteries. This is 
an attractive theory, and would be satisfactory if it 
could be shown that such symmetrical regions of the 
brain only were always involved. A lady who comes 
occasionally to my office, has been subject, for several 
years, to attacks of inferior hemiopia coming on sud- 
denly every four or five months, preceded by no 
warning, and followed by no other symptom. She is 
in good health, and is not of an hysterical or nervous 
temperament. The attack lasts fifteen or twenty 
minutes, during which the field of vision is hounded 
by a sharp, perfectly horizontal line, and all below 
this is in the blackness of darkness. She has some- 
times been seized on the street, and, being unable to 
see her feet or the ground for some distance in front 
of them, has been greatly embarrassed to find her way 
home. I believe that this case, which gives no aid 
or comfort to either theory of decussation, is unique, 
and that, in the present state of medical science, it 
does not admit of intelligent explanation. 
Doubtless there are still many more things in the 
anatomy and physiology of the brain than are dreamt 
of in our philosophy, and it must be admitted that 174 
HARLAN, HEMIOPIA. 
cerebral pathology is not, as yet, a good field for 
complacent dogmatism ; since so many cases are on 
record in which the most definite and unmistakable 
post-mortem revelations have been preceded by symp- 
toms of the wrong kind, or on the wrong side, or in 
which the entire absence of symptoms has bid defi- 
ance to all theories : but perhaps few of these theories 
rest on a firmer basis of physiological experiment, 
clinical observation,' and post-mortem evidence, than 
that of the semi-decussation of the nerve-fibres in the 
optic chiasm. 
Supposing the theory of semi-decussation to be 
correct, an interesting point in the minute anatomy 
of the retina, that must depend upon the study of 
hemiopia for its elucidation, is the distribution of the 
nervous filaments at the dividing line between the 
two halves of the retina. The observations upon the 
exact position of the line of demarcation in hemiopia 
have been too few, and not sufficiently in accord with 
each other, to be much more than suggestive : as 
illustrated by the first case reported above, this line 
may even vary very considerably at different stages 
of the disease, while still continuing perfectly sym- 
metrical in the two eyes. It is a significant fact, 
though, that whenever observers have not contented 
themselves with stating that half the field of vision 
has been obliterated, but have been careful to define 
the limits of the obscured portion with accuracy, it 
is found that this portion has been a little less than 
half. This, as far as it goes, supports the theory of 
Hirschberg, that there is a retinal zone, of about six 
degrees, which would be halved by a vertical line 
drawn through the point of fixation, supplied in 
common from both optic tracts.