(i) The presence of a fluid vitreous, the patient having had the lens of the other eye extracted with bad results. (ii) In the insane, where it would be impossible to carry out the after-treatment of extraction satisfactorily. =Operation.= The operation is usually done under cocaine; in the case of the insane a general anæsthetic is usually necessary. It has been performed by simple depression of the lens backwards into the vitreous with a needle passed through the cornea (anterior route). This operation yields unsatisfactory results owing to the lens being liable to return into the pupil; this can be partly overcome by sweeping the needle round the periphery of the lens so as to divide the suspensory ligament, but the operation is not so satisfactory as when the needle is passed in from behind the ciliary body and the lens pressed down from behind (posterior route), to which the following description applies. The capsule of the lens should be torn freely, so that some absorption may subsequently take place and diminish the risk of complications. =Instruments.= Speculum, fixation forceps, needle. _First step._ The pupil should be dilated with atropine. The patient’s head should be well raised on the table. The needle is passed through the sclerotic about 5 millimetres behind the limbus to the outer side. The posterior capsule of the lens is then freely divided by a sweeping movement. _Second step._ The needle is next made to appear in the lower part of the pupil by carrying it round the lower and outer border of the lens. The anterior capsule is then freely divided. _Third step._ The shaft of the needle is laid flat on the surface of the lens towards its upper part, and by raising the handle of the needle the lens is displaced backwards into the vitreous. The tearing of the suspensory ligament on the inner side may be assisted by the cutting edge of the needle during depression. =Complications.= _Immediate._ Difficulty may be experienced in making the lens lie at the bottom of the vitreous, and it is only by frequent depression of the lens backwards and downwards, with a sweeping movement of the needle to divide the suspensory ligament, that the desired effect can be obtained. _Remote._ The lens nucleus may prolapse through the pupil into the anterior chamber. If this should happen, the patient should be placed on his back and the pupil dilated with atropine; if the nucleus does not go back into the vitreous chamber it should be depressed by means of a needle passed through the cornea. Glaucoma may result from the dislocation of the nucleus into the anterior chamber and should be treated as described above. It may also be present with a lens which is dislocated backwards. This condition is very liable to end in loss of sight. Probably the only hope of relieving the tension is by the use of eserine or the performance of a cyclo-dialysis. Cyclitis and retinal detachment may also follow, and usually end in blindness. CHAPTER III