Maintaining alignment of the visual axes depends on coordinating the movement of both eyes. External examination may reveal obvious clues for the etiology of the patient’s diplopia, especially if proptosis or ocular redness is present. The movement of the eyes should be assessed in all positions of gaze, both individually (ductions) and together (versions).
It is important to establish whether ocular misalignment is comitant or incomitant. Comitant misalignment is often present in congenital strabismus, whereas incomitant misalignment is evidence of an acquired disorder, except in rare cases. Abnormal ductions can often be recognized by gross observation, but formal measurement of the amount of misalignment with a prism and alternate cover test (PACT) is used to determine (quantitate) whether an ocular misalignment is comitant or incomitant.
The Maddox rod test, a sensitive method of obtaining quantitative information about the degree and pattern of ocular misalignment (Fig 7-1), can help reveal subtle cases of strabismus. When viewing a light source through a red Maddox rod, which contains a series of parallel cylinders, the patient sees a line perpendicular to the orientation of the cylinders. Typically, a red Maddox rod is placed in front of the right eye, producing a red line, while the left eye views the fixation light. Viewing such disparate images often makes it easier for patients to appreciate the misalignment of the visual axes. Because this test dissociates the 2 eyes, patients who have a phoria will also report separation of the images on Maddox rod testing. Therefore, it is often useful to combine the subjective results of Maddox rod tests with the more objective results of the simultaneous PACT. PACT is used to determine the manifest deviation, paying attention to the pattern of misalignment in all 9 positions of gaze (and, in some cases, to head tilt).
The double Maddox rod test helps identify and quantify torsional misalignment when vertical diplopia is present. Traditionally, a red Maddox rod is placed in front of the right eye and a white Maddox rod in front of the left eye (Fig 7-2). Because patients may assume that the white line is oriented correctly and falsely localize the abnormal torsion to the red line (right eye), this test is best performed with a red lens in front of each eye.
Figure 7-1 Maddox rod shown with the ridges held vertically, which causes the patient to see a horizontal red line. In this example, the light seen by the left eye is under the red line, indicating a left hyperdeviation, which increases on down right gaze. This finding is compatible with left superior oblique dysfunction.
Figure 7-2 Double Maddox rod test for extorsion. A, A patient with vertical diplopia sees the red line below the white line, indicating a right hypertropia. B, With cyclotorsion, the 2 lines do not appear parallel. The red Maddox rod is then rotated (large arrow) until the 2 lines appear parallel. The degree of rotation required to make the lines appear parallel (in this case about 12°) quantitates the amount of extorsion.
(Used with permission from Kline LB, Bajandas FJ. Neuro-Ophthalmology Review Manual. Rev. 5th ed. Thorofare, NJ: Slack; 2004. Originally modified from Van Noorden GK. Atlas of Strabismus. 4th ed. St Louis: Mosby; 1983.)
A qualitative method for detecting relative cyclotropia uses a horizontal line. A basedown prism is placed over 1 eye to dissociate the images such that 2 vertically displaced lines are visible. The patient is asked whether both lines are parallel or if they converge to 1 side. A cranial nerve (CN) IV palsy is typically associated with convergence of the lines toward the side of the palsy. A CN IV palsy may also be suspected if indirect ophthalmoscopy reveals appreciable extorsion of the ipsilateral fundus (ie, the fovea appears above the superior margin of the optic nerve head).
The presence of ocular deviation may be signaled by a consistent head tilt or head turn on examination. Old photographs (eg, a driver’s license photograph) may provide evidence of chronicity.
Simons K, Arnoldi K, Brown MH. Color dissociation artifacts in double Maddox rod cyclodeviation testing. Ophthalmology. 1994;101(12):1897–1901.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.