synoptophore

The synoptophore, also called the major amblyoscope, is an instrument for investigating binocular vision. Each eye views its own target, similar targets test sensory fusion, and moving each target independently tests motor fusion.¹ The instrument compensates for the angle of strabismus and can therefore test the potential for binocular function in the presence of a manifest deviation.²

Each eye looks down a cylindrical tube with a mirrored right-angled bend and a +6.50 D lens in the eyepiece, which sets the testing distance at about 6 m.² The synoptophore can measure horizontal, vertical and torsional misalignment at the same time, and readings in the cardinal positions of gaze help in planning surgery.² The examiner measures the deviation by moving the arms until the image of each target falls on its fovea.³

The synoptophore grades binocular vision in steps, beginning with simultaneous perception of two dissimilar pictures such as a bird and a cage.² It also detects suppression and abnormal retinal correspondence, and children from about age 3 generally enjoy the test.² Deviations measured in the distance setting are often larger than those found with the prism and cover test at distance, because the targets sit close to the eyes and bring proximal convergence into play.³ The eyes also behave differently in this artificial setting, and the synoptophore, once the principal instrument for treating strabismus, is now rarely used even in hospital clinics.^1,4