A stereo-fixation apparatus for use with bjerrum screen

The fact that binocular fixation is more constant than the monocular method makes the stereoscopic campimeter more accurate than the monocular instrument. In addition, this method allows records to be obtained of central blind areas. In previously existing stereo-campimeters the Brewster type of stereoscope has been employed. These instruments have the disadvantage that the test is made upon a small screen and that the field is limited on the nasal side by the usual septum between the two fields. This paper describes a new apparatus giving stereoscopic fixation for use with a large Bjerrum screen and allows a field of examination of 35? in all directions from the centre. The apparatus consists of a simple optical system which presents to the eye not under test a magnified image of a small design which is the stereoscopic counterpart of a design seen by the other eye at the centre of the Bjerrum screen. The images obtained by the two eyes are fused, giving stereoscopic fixation. Means of adjustment for muscle imbalance is provided. The exploration of the field of vision is carried out in the usual manner. The paper contains a copy of a record made with the new apparatus of a central scotoma in a case of old atrophy of the macula.