The Lability Test.

Methods The test is a combined one. One hand is put into ice-cold water and at the same time constriction is applied to the neck in order to increase the venous pressure in the head. The latter is done by means of an ordinary sphygmo-manometer with the blood pressure cuff round the neck. We have only used a pressure of 40 mm. Hg. in the cuff. Bloomfield (1947) and Bloomfield and Kelterman (1947) use a pressure up to 60 mm. Hg., but many patients complain when such a high pressure is used and we have therefore reduced it. The test lasts only one minute and the ocular tension is measured with a Schibtz X-tonometer after half a minute, and after one minute. The rise in tension is recorded. In some cases we have done the ice-water test and the neck compression test (the " cuff " test) separately, and then the combined, lability test. In order to find out what really happens in the eye during the test, we have, in addition to measuring the ocular tension, also observed the aqueous veins and measured the pressure in an episcleral vein. This venous pressure is measured with a water manometer previously used by one of us and a fuller description of the method has been given by Thomassen (1947a). The water in the manometer is connected by rubber tubing to a transparent chamber, one side of which is composed of thin cellophane. This side is placed over the vein, which can be clearly seen through the transparent chamber, and the pressure required to collapse the vein is then read on the manometer. We have examined normal eyes, and eyes suffering from simple glaucoma. In all, 52 normal persons have been examined. The ice-water test has been applied separately to thirteen of them. This test did not alter the pressure in the episcleral veins in any case, nor did the appearance of the aqueous veins change except in one case, in which a definite increase in the outflow of clear liquid was seen in the aqueous vein. This patient was the only one who had a definite increase in ocular tension during the test. This means that the increased intra-ocular pressure was combined with