junctiva. In the three first positions the displacement is only partial and the margin of the lens can be seen by oblique illumination occupying some part of the pupil.

In displacement forwards the pupil will be found dilated, irregular in shape, and fixed; oblique illumination will show the lens lying partially or entirely in the anterior chamber.

In displacement backwards the iris will be tremulous, the pupil sluggish, and the anterior chamber deepened. Direct ophthalmoscopic examination will probably detect the lens lying in the ciliary region at the lower part of the eye.

In displacement beneath the conjunctiva the lens is found forming a small rounded tumour somewhere near the corneal margin most frequently at its upper part.

Treatment.—If the lens is displaced partially, or into the anterior chamber and still retains its transparency it may be left alone. But should it become opaque it must be removed by extraction, or an artificial pupil may be made in such a position as to allow of light entering the eye by the side of the opaque lens. If the lens sets up irritation it must be extracted with a scoop, or sharp hook, iridectomy being performed at the same time, if it has not already been done (see Extraction, Part II., Chap. V.) some vitreous will probably be lost during the operation.

A transparent lens may remain for years in the anterior chamber, and, with the exception of impairment of vision, give rise to no inconvenience. If its capsule has been ruptured, however, it will become opaque and if not extracted will be removed by absorption. A lens displaced into the vitreous chamber will very probably act as a foreign body, and set up glaucomatous changes

in which case it should be removed at all risks; but if it causes no irritation it is best left alone.

A lens displaced beneath the conjunctiva may be left alone or removed at discretion.

Cataract will be considered in the section on operations.

CHAPTER VIII.

THE IRIS AND CHOROID.

CONGENITAL ANOMALIES.

Coloboma.-A cleft condition of the iris or choroid, dependent on failure of closure of the foetal fissure is known as "coloboma." In the iris it occurs as a deficiency of the lower segment, appearing as if iridectomy had been performed downwards; in some rare cases the cleft is above. In the choroid it is seen (on examination with the ophthalmoscope) as a brilliant white figure, commencing at the optic disc, and continuing downwards and forwards for a variable distance towards the ciliary processes, through which, in extreme cases, the cleft extends and is even continuous with a similar deficiency of the iris.

Central deficiency. In some cases a central nearly circular hole is met with in the choroid as a congenital defect.

In the albino the pigment of the iris and choroid is absent to a greater or less extent, and with the ophthalmoscope the fundus of the eye appears of a yellowishwhite colour, and traversed by innumerable blood-vessels. Irideremia, or congenital absence of the iris, is occasionally observed.

Persistency of the pupillary membrane.-Small portions of the membrane, which at a period of fœtal life covered the pupil, occasionally remain, and are seen as one or more fine threads, somewhat resembling cobwebs, passing across the pupillary area, and attached at either end to the anterior surface of the iris, near the margin of the pupil. The thread is often double at one end and single at the other.

Anomalies of colour.-The irides in the two eyes may be different colours; thus the colour in one eye may be brown, whilst that of its fellow is blue, or differences in colour may occur in different parts of the same iris.

TREMULOUS Iris, Tumours.

Tremulous iris (iridodonesis) signifies a tremulous condition of the iris, which shakes about as the eye is moved. This condition is met with when the iris has lost the support of the crystalline lens, when the vitreous humour is abnormally fluid, or the iris totally paralysed.

Tumours seldom originate in the iris itself, but its structure often becomes implicated by growths commencing in deeper parts of the globe (see Tumours of Eyeball). Instances, however, of malignant growths, dermoid and simple cysts, and of the cysticercus, have been met with in the iris.

INFLAMMATION OF THE IRIS (IRITIS).

Causes. The causes of iritis are local and constitutional, most cases, however, are of the latter origin.

Local.-Irritation from foreign bodies in the conjunctival sac or cornea; friction of the cornea by granular lids or inverted lashes; injuries to the iris itself by operations, or accidents, with or without the lodgment of foreign bodies in its substance or on its surface; pressure by a swollen crystalline lens, exposure from perforation of the cornea, and exposure to cold, especially draughts.

Constitutional.-Debility after acute disease, overlactation, etc.; certain specific diseases, as syphilis, rheumatism and gout.

Symptoms.-The following symptoms are met with in most cases of iritis: changes of colour, cloudiness and

loss of polish of the iris, sluggishness or complete immobility and (as a rule) contraction of the pupil, injection of the ciliary region (ciliary redness), watering of the eye, and impairment of vision. Other symptoms met with occasionally are pain, intolerance of light, irregularity in outline of the pupil, inflammatory products-pus or lymph nodules-visible to the naked eye. Three varieties of iritis are commonly met with. I. Simple iritis. 2. Recurrent or rheumatic iritis. 3.

Syphilitic iritis.

Simple iritis.-All the more constant symptoms of iritis are present, often accompanied by more or less severe pain. An uncomplicated attack lasts from one to two weeks or longer, and usually ends in resolution, the iris quite recovering its normal condition, but a few adhesions may form between the iris and lens-capsule (posterior synechia). In this as well as in the other forms of iritis, however, the inflammation may run on to the formation of a considerable quantity of new material or into suppuration. When suppuration takes place, the iritis is sometimes described as a separate variety "suppurative iritis." Iritis accompanied by the production of clear fluid causing the anterior chamber to appear unusually deep is described as serous iritis." Serous iritis is sometimes met with after operations for cataract and may be a source of considerable danger to the eye. It is generally accompanied by slight-at times by great -increase of tension of the globe.

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Recurrent or rheumatic iritis occurs in persons who are subject to attacks of rheumatism, (more especially gonorrhoeal rheumatism), or gout, and also in the children of rheumatic or gouty parents; an attack of this form of inflammation presents all the more constant symptoms of iritis, and has one character peculiar to itself, viz., its tendency to recur, some patients having