=Indications.= Iridectomy for optical purposes is performed for a centrally situated nebula of the cornea and in some very rare cases of small central opacities in the lens. In the latter condition it is rarely of much value, as nearly all the rays which enter the eye pass through the central portion of the lens. Further, in this condition the lens may be removed and better sight obtained with glasses. Optical iridectomy should always be performed opposite a clear portion of the cornea, the lower segment of the eye being chosen, otherwise the coloboma may be subsequently covered by the upper lid. The site of election for the operation is downwards and inwards, but in all cases the patient should be carefully examined in the following ways: (1) the vision is tested, any refraction being corrected without a mydriatic; (2) the pupil is then dilated, and the best situation for the iridectomy determined by means of a stenopaic slit. The vision must be definitely improved by the use of these before operation can be advised. The disadvantage of an iridectomy is that it allows more light to enter the eye, and, if the periphery of the lens be uncovered, spherical aberration may result. For both these reasons, therefore, it is advisable to make the iridectomy as small as possible. Tattooing of the central scar in the cornea will often diminish the amount of light entering the eye, but before undertaking the latter operation, the eye should be cocainized and the area covered with a piece of black paper to see if the vision is improved thereby. [Illustration: FIG. 107. OPTICAL IRIDECTOMY. The incision being made with a keratome.] =Instruments.= Speculum, fixation forceps, bent broad needle or small keratome, Tyrrell’s hook, iris forceps, scissors, and spatula. =Operation.= The operation is usually performed under cocaine. _First step._ The eye is fixed by grasping the conjunctiva directly opposite the spot at which the incision is to be made. The incision is then made by means of a keratome or bent broad needle directly behind the limbus, and enlarged laterally if desired (Fig. 107). _Second step._ A Tyrrell’s hook, bent at the correct angle, is passed on the flat into the anterior chamber. When the margin of the iris is reached the handle is rotated and the hook is made to engage the free border of the iris, which is then withdrawn from the wound; a small portion is removed with scissors, which should be held at right angles to the wound when dividing the iris (Fig. 108). [Illustration: FIG. 108. OPTICAL IRIDECTOMY. Method of removing the iris to produce a small coloboma.] _Third step._ The iris should be carefully replaced and the pupil kept under the influence of eserine until the anterior chamber has re-formed, when atropine should be substituted.