[Tension under controlled conditions in the encircling operation (author's transl)].

The complications, which occur in encircling-operations, such as String-Syndrome, scleral Nekrosis, glaucoma-development (due to narrowing the anterior chamber) as well as closure of the central artery most frequently happen, when the globe has been tightened too much. From the calculations we have make using the cerclage element in reducing the circumference and volume (Fig. 2) we have shown that an identation of the sclera more than 3 mm deep is not advisable. The Silicon-Cerclage-Materials, which we use, are tested by the tension-testing machine, which determines the modulus of elasticity. The stress, that is force per sectional area, is determined in relation to the amount of elongation in the material (Fig. 3). A round silicon rod with a diameter of 2 mm and a modulus of elasticity between 150 and 200 p/mm2 proved most effective. In addition, we have conducted experiments with the Cerclage-rods on enucleated human eyes (Fig. 4). In one experiment the intraocular pressure was determined in relation to the pull of the weight upon the globe (Fig. 5). In a second experiment the reduction of the circumference was related to the height of the intraocular pressure (Fig. 6). The elastic Cerlage-rod has the advantage of creeping, when tensed, it tries to regain its original length. However, the globe, owing to the pressure within it, works against the creeping. With the help of the stress-strain diagram (Fig. 7) and the experiments on the human eye we can determine more accurately the degree of the creeping. In index 1 we can see how much the circumference has been finally reduced including the creeping in relation to the height of the intraocular pressure. The intraocular pressure should not be increased above 35 mm Hg. Otherwise: 1. the circumference of the globe will be considerably more reduced; 2. the intraocular pressure will rise much more slowly when compared to results at the lower eye-tension and 3. the volume reducing-effect will diminish markedly. It is important to measure the intraocular pressure before the end of the operation in order to avoid the above mentioned complications.