The operation has for its object the separation of the ligamentum pectinatum from its attachment to the sclerotic, with the probable result that the ciliary body and iris root become retracted by the ciliary muscle, so that the canal of Schlemm is opened up and again communicates with the anterior chamber. It also opens up a free communication between the anterior chamber and the suprachoroidal lymph-spaces. The reduction of tension is often not fully manifest for about ten days after the operation. =Instruments.= Speculum, fixation forceps, Graefe’s knife, fine pair of straight iris forceps, fine pair of sharp-pointed straight scissors, iris spatula. =Operation.= The operation is best performed under a general anæsthetic, as it is attended with considerable pain, although cocaine and adrenalin are frequently used and are always advisable, since the hæmorrhage from the scleral vessels renders it difficult to gauge the depth of the wound in the sclerotic. [Illustration: FIG. 120. CYCLO-DIALYSIS OPERATION. Showing the spatula separating the ciliary body and ligamentum pectinatum from the sclerotic.] _First step._ By means of the straight iris forceps and sharp-pointed scissors a semilunar conjunctival flap is first raised over the site for the scleral incision. The incision in the sclerotic should be situated about 5 mm. behind the corneo-sclerotic junction over the ciliary region, the outer and upper quadrant of the eye being the easiest position for subsequent manipulation (Fig. 119). _Second step._ With a Graefe’s knife the fibres of the sclerotic are carefully divided in an oblique direction forward until the suprachoroidal lymph-space is opened for about 3 mm. The first part of the incision is performed with the blade and completed with the point of the knife, the anterior flap of sclerotic being held forward by straight iris forceps. Heine uses a keratome, dividing the fibres of the sclerotic with the point by stroking it along the line of the incision. The depth of the incision should be carefully gauged from time to time with the iris spatula; the pigment of the ciliary body is usually seen in the bottom of the wound when the sclerotic has been penetrated. _Third step._ The iris spatula is directed forwards and inserted between the sclerotic and the ciliary body, keeping close to the former. With a gentle side-to-side movement the spatula is made to separate the ciliary body from the sclerotic for about one-eighth of its whole circumference; then the ligamentum pectinatum is detached from the sclerotic for about the same distance by gently passing the spatula forwards and making the latter appear in the anterior chamber (Fig. 120). If it be desired to evacuate the anterior chamber, the spatula is slightly rotated so as to allow the escape of the aqueous. As a rule this is not necessary or even advisable. The spatula is then withdrawn and the conjunctival flap is replaced in position. Eserine should be instilled.