Typical accommodative squint occurs quite independently of the will on
each effort of the accommodation, and is not combined with diplopia. It
is otherwise in those cases of hypermetropia of high degree in which
patients voluntarily call forth convergent squint, and retain it for a
short time for the purpose of distinct vision. They are then perfectly
conscious of the squint, and perceive also as a rule the double images
which occur at the same time; I have seen such cases in adults who could
only produce the accommodation necessary for distinct vision by the aid
of a too strong convergence; they, however, only now and then made use
of this help. Although differing much from the typical form, these cases
of voluntary accommodative squint were also included in the statistics.
In involuntary periodic (even if not accommodative) squint, the patient
as a rule is not conscious of the occurrence of the false position; that
exceptions to this occur Case 1 has given us an instance.
CONVERGENT SQUINT IN MYOPIA.
For the ætiology of convergent strabismus it is of interest to ascertain
the age at which it is developed, and one of the first results we obtain
is the exceptional position which the union of myopia with convergent
strabismus takes in this category. Of the 56 cases contained in the
above statistics I possess reliable information of the time of
commencement in 11 cases; the squint was twice observed before the
fourth year of life, once between four and ten years of age, eight times
between the tenth and thirty-third years of life.
I must first state prominently with regard to the connection of myopia
with convergent squint that I see no reason for holding short sight to
be the cause of the squint, as v. Graefe does.
A specially severe strain of the eyes, as v. Graefe assumes, was not
traceable in the cases observed by me. Excessive convergence and strain
on the accommodation is often enough present in weak sight, for example,
in astigmatism without the existence of squint; were short sight in
general an inducement to convergent squint these cases would appear much
oftener than they actually do, owing to the frequency of myopia. In my
opinion the cause of their rarity lies in the fact that myopia is
frequently combined with insufficiency of the interni and preponderance
of the externi, but only rarely with the reverse condition of the
muscles. If, however, a preponderance of the interni develops itself
together with the myopia, convergent strabismus is easily produced, for
without correction of the myopia by spectacles, the desire for retaining
binocular single vision for everything beyond the far point is lessened
by the indistinctness of the retinal images. Within the range of their
field of distinct vision these squinting myopes frequently retain
binocular vision, while the capacity for accepting parallel rays or
retaining them for long, is lost.
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