cheiroscope

A cheiroscope is a Brewster-type instrument that presents a printed target to one eye and a blank sheet of paper to the other. The patient looks into the instrument and traces the target onto the blank sheet with a pencil.¹ Clinicians use the cheiroscope to assess binocular stability, binocular alignment and suppression, and as a therapy device to improve binocular stability and reduce or eliminate suppression.¹

For the diagnostic tracing, the blank side goes in front of the eye on the side of the dominant hand.¹ Corresponding points in the finished tracing that sit 77 to 80 mm apart represent orthophoria. A wider separation indicates an exophoria posture, and a narrower one an esophoria posture.¹ A tracing placed higher or lower than the original reveals a vertical phoria. Disappearance of the pencil or parts of the picture indicates suppression, and drifts in the tracing indicate binocular instability.¹

Cheiroscopic tracing suits the last phase of therapy for divergence excess, because it presents stimuli under the most challenging conditions.² Patients with divergence excess find the tracings hard at first, because the stimuli offer little structure and sit at optical infinity.²