Performing an examination

The patient sits 50 cm in front of the screen the mid-point of which is situated in his main direction of gaze. He looks through the red and green goggles fastened to the headrest. The green lens is in front of the left eye. To investigate the muscle functions of the left eye the ophthalmologist switches on the red fixed points in the 20° field. This means that the patient sees the red fixed points with the right eye through the red lens of the goggles. Then he is asked to direct the arrow of the light pointer, automatically lighting up in green, which he guides himself using the hand he writes with, onto the red fixed point. This means that the patient sees the green light spot with the left eye through the green lens of the goggles. When the fixation point changes, his direction of gaze changes as well. The ophthalmologist records on his chart, which is on the remote control and which is illuminated from below, the sites of the points given by the patient in the corresponding field. When the position of the green light arrow is recorded in the 9 main directions of gaze the muscle functions of the right eye are tested in the same way, during which the fixed points are illuminated in green.

Normally measurements should be taken at 20°. Small strabismic deviations are diagnosed more easily if measured at 30° or 40°. In the case of very severe strabismus measurements can also be taken at 10°.