In the course of an examination with the slit lamp, an attempt is usually made to keep the subject's eyes stationary, and yet directed straight ahead, by having him fixate on the examiner's forehead or on some part of the microscope. While probably satisfactory for all practical purposes, the procedure has several disadvantages: The observer's head and, to a less extent, the microscope are not themselves stationary; they are not visible when the examination is done in a dark room, and they are so close to the subject that fixation is tiring for the presbyopic or prepresbyopic patient.
To overcome these difficulties and to permit a ready variation in fixation, we have found the following procedure satisfactory for all but one-eyed patients. Two mirrors about 5 cm. in diameter are attached to the chin rest base by means of a flexible cable1 in such a way that each mirror
DONALDSON DD, COGAN DG. A FIXATION AID FOR SLIT LAMP BIOMICROSCOPY. Arch Ophthalmol. 1950;43(3):555-556. doi:10.1001/archopht.1950.00910010564018