Noncomitant deviations are when the amount of misalignment changes as the gaze direction changes. Clinically, if the difference in the deviation between gaze positions exceeds 5 prism diopters, it’s considered noncomitant. This threshold helps separate true changes in alignment due to a restricted or palsied muscle from small measurement variances that can occur with exam technique. For example, you might find a large angle in one gaze and a noticeably smaller angle in another, with the difference over 5 PD, indicating noncomitance. If the variation is only a couple of prism diopters, it could be within normal measurement fluctuation and doesn’t necessarily indicate a noncomitant deviation. So, the standard criterion is a difference greater than 5 prism diopters between gaze positions. Differences larger than this (such as greater than 10 PD) still fall under noncomitance, but 5 PD is the defining threshold.

Duane retraction syndrome in Type I shows a clear pattern: the eye cannot move outward well, so abduction is limited, while inward movement (adduction) is relatively preserved. This happens because the lateral rectus is not properly innervated, often due to a malformed or absent abducens nerve, so outward movement is diminished. When the eye is asked to look inward, co-contraction of the medial rectus with the misinnervated lateral rectus can pull the globe back into the orbit, causing globe retraction and a narrowing of the palpebral fissure. That combination—restricted abduction with preserved adduction and characteristic globe retraction on adduction—defines Type I. The other patterns fit Type II (adduction limited) or Type III (both directions limited), while no restriction would be normal motility.

Suppression testing aims to determine whether one eye’s input is being inhibited by the brain to avoid diplopia, and this is best revealed when the two eyes are presented with distinct, separate images that don’t constantly force fusion. Bagolini lenses provide a very gentle, binocular dissociation. When a patient looks at a fixed target through paired, fine-line lenses, each eye sees a faint line that, if fusion is intact, the brain combines into one percept. If one eye is suppressed, the lines may appear incomplete or the patient may report seeing lines from only one eye or in disrupted locations. The patterns map where suppression occurs and how extensive it is, without creating a strong diplopic situation. Red-green filters (or Bangerter filter tests) place translucent color filters in front of each eye and present red and green targets. The patient reports which color image they see and where. If suppression is present, the image from the suppressed eye won’t be seen, or the colors won’t fuse, revealing the eye’s suppression and often its extent. This method directly probes the interocular image competition and is a practical alternative to Worth 4-dot for identifying suppression. Other common tests have different purposes. The Maddox rod test mainly breaks fusion to measure ocular misalignment (phorias) under dissociation, so it’s more about quantifying deviation than mapping suppression patterns. The cover test assesses alignment by alternating occlusion but doesn’t describe which eye is suppressed or how suppression varies across the visual field. Stereoacuity testing evaluates depth perception and the functional outcome of binocular fusion, but it doesn’t systematically map which eye is suppressed or how suppression is distributed. So, Bagolini lenses and red-green filter approaches directly illuminate suppression patterns and are therefore the primary alternatives to Worth 4-dot for this purpose.

Listing's plane is the plane in which the eye’s rotation axis lies when moving from the primary position; eye orientation to any gaze can be represented by a single rotation about an axis that lies in that plane. In the standard NBEO coordinate convention, the vertical direction within Listing's plane aligns with the Z axis, so the axis that serves as the vertical one in Listing's plane is Z. This is why the vertical axis in Listing's plane is Z.