during screaming_.--We have seen that infants and young children,
whilst screaming, invariably close their eyes firmly, by the contraction
of the surrounding muscles, so that the skin becomes wrinkled all around.
With older children, and even with adults, whenever there is violent
and unrestrained crying, a tendency to the contraction of these same
muscles may be observed; though this is often checked in order not
to interfere with vision.

Sir C. Bell explains[12] this action in the following
manner:--"During every violent act of expiration, whether in
hearty laughter, weeping, coughing, or sneezing, the eyeball
is firmly compressed by the fibres of the orbicularis;
and this is a provision for supporting and defending the vascular
system of the interior of the eye from a retrograde impulse
communicated to the blood in the veins at that time.
When we contract the chest and expel the air, there is a
retardation of the blood in the veins of the neck and head;
and in the more powerful acts of expulsion, the blood not only distends
the vessels, but is even regurgitated into the minute branches.
Were the eye not properly compressed at that time, and a
resistance given to the shock, irreparable injury might be
inflicted on the delicate textures of the interior of the eye."
He further adds, "If we separate the eyelids of a child
to examine the eye, while it cries and struggles with passion,
by taking off the natural support to the vascular system
of the eye, and means of guarding it against the rush of blood
then occurring, the conjunctiva becomes suddenly filled with blood,
and the eyelids everted."