Duane Retraction Syndrome (DRS) is an oculomotor anomaly principally affecting one eye resulting in a paretic strabismus and compensatory face turn to favor the field of fusion. There is classically a narrowing of the palpebral fissure when looking toward the affected side due to co-contraction of extraocular muscles that results in a subtle retraction of the paretically-involved eye. DRS comes in three basic types along with three basic subtypes. The number designation focuses on the direction of strabismus:
- Type 1: Limited abduction with or without esotropia
- Type 2: Limited adduction with or without exotropia
- Type 3: Limitation of both abduction and adduction and any form of horizontal strabismus
The subtypes characterize the limitation of movement:
- Type A: Limited abduction with less limited adduction
- Type B: Limited abduction with normal adduction
- Type C: Limited adduction with less limited abduction. There is an exotropic deviation and a head turn to compensate the loss of adduction
Here is an online video example of a patient with Type 2C. It is his left eye that is affected, with limited adduction, while abduction is relatively normal. For unknown reasons, it is typically the left eye that is affected in unilateral Type2C cases of mis-wiring in DRS.
Here is a teenager I saw yesterday who, when seated in the examination chair habitually turns his face to the right, much like the child in the video above.
With his face in primary position without the turn, and as he looks leftward, it is apparent that his left medial rectus is unable to adduct or move inward to the nose to follow his right eye moving to the right side. The left eye remains straight, effectively resulting in exo diplopia as the patient looks rightward.
The more the patient looks to the right, the greater the exo diplopia of the left eye as it remains fixated on midline. Although narrowing of the fissure and retraction of the left eye is not evident here, it was dramatic while conducting a cover test which unfortunately I didn’t capture on video.
Looking to the left side presents no problem, as abduction of the left eye is normal.
Glancing at the top photo again, the patient habitually substitutes face turning to the right which enables the two eyes to stay relatively aligned and favor looking on midline or gazing leftward. So the best case typing for our patient would be Duane Type 2C.
Patients with problems in unilateral adduction deficit due to weak signaling from CNIII on the affected side, or weak medial rectus response, will have difficulty maintaining normal convergence. As occurred with our patient, low exophoria at distance (6^ exo) and greater exophoria at near (16^ exo) has resulted in convergence insufficiency in the plane of his normal adaptive face posture. In some cases of Type 2C yoked prism bases right may be of benefit to re-position right field toward the region of better fusion, but the patient did not respond favorably to this. He responded preferentially to 3^ base-in compensatory prism. Certainly vision therapy is a possibility to bolster convergence.
But it gets a bit more interesting. The patient also experiences diplopia in upgaze or downgaze. The diplopia is more noticeable on upgaze, due to greater limitation in elevation of the left eye than it is on downgaze.
Based on principles described in this article, I incorporated a low amount of vertical compensatory prism as well (in this case 1^ base down OS) which provided best binocular balance along with the 3^ BI noted above. Complicating matters further is the fact that the patient was diagnosed with diabetes several years ago and has had difficulty controlling his HbA1c until recently.
Prism and therapy aside, surgery is not a consideration in this case for obvious reasons. Ergonomic counseling was provided to the patient and his family. This young man is consumed with learning and reading text material most of the day, and he was counseled to position himself or his texts so they are either centered or on his left side. Given that the primary vertical plane was best for fusion, he was also advised to obtain an adjustable desk-top book holder enabling him to remain perpendicular to the text page as much as possible.