CHAPTER 8
The Patient With Diplopia
Diplopia is among the most common symptoms for which patients seek ophthalmic care. The following important questions offer substantial insight into the nature of a patient’s particular condition:
Does the double vision resolve when either eye is covered (monocular vs binocular diplopia)? Is the double vision the same in all fields of gaze (comitant), or does it vary with gaze direction
(incomitant)?
Is the double vision horizontal, vertical, oblique, or torsional? To what extent is diplopia constant, intermittent, or variable?
History
Patients in whom an ocular misalignment develops may report double vision or simply “blurred vision.” The cause of blurred vision can often be inferred to result from ocular misalignment (ie, diplopia) if closing either eye eliminates the visual disturbance (“binocular blur”). In contrast, monocular diplopia is usually optical but can occasionally be confused with metamorphopsia secondary to a maculopathy.
It is often helpful to determine if double vision is more bothersome with far or near fixation, or in a particular position of gaze. A history of head or eye pain, numbness, eye or eyelid swelling or redness, or other neurologic symptoms provides clues about possible orbital, cavernous sinus, or central nervous system causes of diplopia. A history of trauma, thyroid disease, or generalized weakness is also helpful in considering a differential diagnosis for diplopia.
Physical Examination
The ability to maintain alignment of the visual axes depends on the coordination of movement of both eyes. External examination may reveal obvious clues for the etiology, especially if proptosis or ocular redness is present. The movement of the eyes should be assessed individually (ductions) and
together (versions). Eye movement should also be assessed in all positions of gaze, with a comparison made in primary position and downgaze (the 2 most frequently used gaze positions) between near and far fixation.
One goal of the physical examination is 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. Assessment of an ocular misalignment is made by a sequential screening strategy. Abnormal ductions can often be recognized by gross observation, but in most cases the alternating cross-cover test (including measurement of the amount of misalignment), performed at all 9 standard positions of gaze, is used to determine whether an ocular misalignment is comitant or incomitant.
With a cooperative patient, subtle cases of strabismus may be revealed by using a red Maddox rod, which contains a series of parallel cylinders. When viewing a light source through the Maddox rod, a patient sees a line that is 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. A red glass can also be used, but it produces a large and somewhat diffuse red light, which frequently makes it more difficult for the patient to perceive misalignment of the images. Because these tests dissociate the 2 eyes, patients who have a phoria may report misalignment of the visual axes. It is therefore often useful to combine the subjective results of Maddox rod tests with the more objective results of the alternate prism cover test, paying attention to the pattern of misalignment in all 9 positions of gaze. Nevertheless, the Maddox rod test is a sensitive method of obtaining quantitative information about the degree and pattern of ocular misalignment (Fig 8-1), as is Hess-Lancaster testing in the 9 positions of gaze.
Figure 8-1 Maddox rod shown with the ridges held vertically, which causes the patient to see a horizontal line. In this example, the light seen by the left eye is under the line, indicating a left hyperdeviation increasing on down right gaze. This finding is compatible with a left superior oblique dysfunction or left fourth nerve palsy.
The double Maddox rod test helps identify and quantify torsional misalignment when vertical diplopia is present. Typically, a red Maddox rod is placed in front of the right eye and a white
Maddox rod in front of the left. When both rods are aligned vertically, the patient perceives 2 horizontal lines of light (red line, right eye; white line, left eye) and can judge if the lines appear parallel or if one is tilted with respect to the other. If tilted, 1 Maddox rod is rotated in the appropriate direction to quantify the amount of torsional misalignment (Fig 8-2).
