LENS, DISEASES OF.
Anomalies.of Position.—Anomalies of position are always the result of changes in the zonula of Zinn.
Classification.—Cases of dislocation of the lens are commonly divided into two groups: in one of which the lens has completely left the fossa patellaris auxa tion, or complete dislocation), while in the other it still remains partly within this cavity (subluxation, or partial dis location); but as it is usually only a matter of time for cases in the latter group to find their way into the former, this distinction only marks a stage in the history of the case.
A more convenient and comprehensive classification can be made on an etiolog ical basis.
Dislocations of the lens are either con genital (ectopia lentis) or acquired.
The latter group may be thus di vided:— 1. Traumatic cases, in which the. lesion varies in degree: (a) There may be a partial displacement, the lens being caused to rotate on its axis, or pushed sideways, thus assuming an oblique posi tion, or a position \vith its edge in the pupil; or it may be displaced sideways and rotated. (b) It may be completely dislocated into the anterior chamber. (c) It may be completely dislocated into the vitreous chamber. (d) It may pass through a rent in the sclerotic, and lie under the unbroken conjunctiva: sub conjunctival dislocation. (e) It may pass through a rent in the conjunctiva. (f) It has been found beneath Tenon's cap sule.
2. The lens niay escape from the eye at the moment of rupture of the floor of a large corneal ulcer: a more common in cident in the cases of ophthalmia neona torum than in any other form of disease.
3. It may be dragged out of position by iridic adhesions when the iris is stretched or rendered tense by the occur rence of peripheral staphyloma.
4. It may be pushed out of position by intra-oeulai tumors.
.5. Its displacement may be spontane ous.
Ectopia lentis seems to depend upon imperfect or incomplete development of the zonula, and, as this developmental failure occurs especially along the line where closure of the ocular fissure takes place, the more perfectly developed fibres at the upper part drag tbe lens in their direction. Consequently con
genital displacements are almost always directly or obliquely upward. They are also usually symmetrical, and are not in frequently accompanied by coloboma of the lens, which, moreover, is apt to be undersized and thicker than normal.
In accordance with the above theory. dislocation of the lens is occasionally as zsOeilliCd ith coloboma of the iris, ciliary bodv. and choroid.
CaSe of double congenital dislocation of the lens in a boy 7 years of age, W110 1,1111S 111$0 partially amblyopie. The lens it: each eye was tilted upward, slightly backward. and inward. .1s.:o other struct ural changes could be detected. Conclu sions that : (1) congenital ectopia lentis is usually double; (2) it is a congenital malformation, the cause of hich is not yet positively established; (3) amblyopia and ametropia are always concomitant conditions, and that the majority of cases, so far reported, sustain the theory of heredity as the primary cause. Priebis (Jour. Amer. Med. Assoc., Sept. 3, '92).
Series of lenses, in number, in which the nucleus was not centrai, but lay close to the posterior capsule, either at the posterior pole or between it and the equator. In all the anomaly must have been due to a developmental disturbance. In some the outline of the lens was nor mal; in 5 others there was a posterior lenticonus. In 3 of these latter the con ical ectasia of the lens-surface was formed by the displaced lens-nucleus, which was actually in contact with the capsule; in the other 2 this was not the case, the lens-fibres lying quite regularly on the little cone. The anterior section of the lens was in all cases normal. Only in 1 case did the lens-capsule, much thinned, cover the lenticonus. C. Hess ("Bericht der Ophthal. Gesell.," Heidelberg-,, '06).