Congenital; acquired; traumatic, softening of suspensory ligament:
hinge motion, lens drops behind iris, protrudes through pupil,
cataract. Apparent increased depth of anterior chamber, tremulous
iris, projecting edge of lens like black ring. Treatment: extraction.
Dislocation of the lens may be congenital, or acquired. In the latter
case it is explained by a traumatism or a liquefaction of the vitreous
and coincident softening of the suspensory ligament. In either case, if
the ligament is torn through in more than one-half its circumference,
the lens will hang by the remainder and move on it as on a hinge so as
to change its location in the different positions of the head. This is
especially so where the vitreous has become abnormally fluid as there is
then no resistance to the free backward movement of the lens. The writer
has seen the eye of a cow affected in this way, so that the cataractous
lens advances to the pupil and recedes from it as the eye is moved. In
other cases the dislocated lens, being attached below only, drops down
and virtually disappears behind the lower part of the iris. In still
other cases it becomes wedged into the pupil, or protrudes into the
anterior chamber and lies in front of the pupil and iris. The
semi-detached lens sooner or later becomes opaque. A cataract with
contraction of the newly formed tissue on the capsule and undue tension
on the suspensory ligament may, however, precede the dislocation which
is then precipitated by some shock, as a blow, fall, sneeze, cough or
emesis.
The condition leads to an apparent increase in the depth of the anterior
chamber, and tremulous movement of the iris, and if illuminated the
impacted condition of the lens or its changes of position can be
detected. If its edge is exposed it appears as a black ring.
_Treatment_ is useless, unless it be extraction of the lens, or
iridectomy in suitable cases.