DIAGNOSTICS
When Eye Strain Isn't Eye Strain
With Duane's Retraction Syndrome, an ordinary complaint may require surgical intervention.
By Jack Prince, O.D., Baltimore, Md.

A thirty-five-year-old female came in with the chief complaint of nearpoint eyestrain associated with computer use. While obtaining the ocular history, she stated that she had a "lazy" left eye. Her previous optometrist, whom she had seen since childhood, prescribed a low-plus reading prescription that was no longer sufficient to eliminate her asthenopia.

	Figure 1: this Type 1 Duane's Retraction Syndrome patient shows limited abduction of the left eye on levoversion.
	Figure 2: Slight narrowing of the palpebral fissure with globe retraction upon adduction of the left eye. While this is an example of minimal globe retraction, it can be pronounced.
	Figure 3: Note the subtle face turn to the left. This positions the left eye in an adducted position in order to maintain fusion. In this patient, the eso-deviation is present in the primary position, increases as she abducts the left eye, and decreases with a slightly adducted posture.

Looking for clues

While the manifest refraction revealed clinical emmetropia and the fundus examination was unremarkable, the motility examination was clearly abnormal. The left eye was unable to abduct past the midline (Figure 1) and there was a slight narrowing of the palpebral fissure upon adduction of that eye (Figure 2). Stereoacuity with the Titmus test measured 40 seconds at near. Twenty prism diopters of base out prism neutralized the deviation at distance and eight prism diopters base out at near. When she adducted the affected left eye, no up shoots or down shoots were evident, but there was slight globe retraction.

Meet Duane

These signs are characteristic of Duane's Retraction Syndrome, a relatively uncommon ocular motility disorder caused by the congenital incorrect innervation of the horizontal rectus muscles. Current medical opinion believes that a branch of the third nerve innervates both the lateral and medial rectus muscles. This co-contraction of the rectus muscles occurs upon adduction of the involved eye and results in retraction of the globe and narrowing of the palpebral fissure. These are the defining signs of this syndrome.

Duane's Retraction Syndrome manifests in several varieties. This patient has Type I, which is the most common variant of Duane's Retraction Syndrome. It results in limitation of abduction combined with relatively normal adduction. Other less common variants have limitations on adduction or both adduction and abduction. All variants of Duane's can have up shoots or down shoots and typically have globe retraction upon adduction.

Identifying coping measures

Upon careful observation of this patient, I detected a subtle face turn toward the adducted left eye (Figure 3). By keeping the affected eye in the adducted position, this compensatory head posture afforded the patient fusion and normal stereoacuity. Because of the magnitude of this deviation, it's not practical to neutralize it with prism. And because I could not optically correct the deviation in order to alleviate the compensatory head posture, this patient needed a surgical solution. (Please note that most patients with Duane's Syndrome do not have a compensatory head posture and do not need surgery or prism. Another patient may have only a slight deviation in primary position and prism might work. Another patient may have no deviation in primary position. Many patients with Duane's fuse in primary position and do not have compensatory head turns.)

Finding a remedy

Because this patient had an abduction deficit without an adduction deficit, I referred her to a pediatric ophthalmologist who performed a bilateral medial rectus procedure. The ophthalmologist recessed the medial rectus muscles by detaching them and reattaching them further back in the globe to weaken the effect of these muscles. This counterbalanced the abduction weakness in the left eye and eliminated the esotropia in primary gaze.

Postoperative measurements in the primary position were orthophoria at distance and three prism diopters esophoria at near. While the post-op refraction in the right eye remained at plano 20/20, the post-op refraction in the left eye changed from +0.25 D.S. preoperatively to 20/20 to pl=+0.75 x 060 20/20. And although the patient had never mentioned "eye muscle spasms" preoperatively, she stated that even without spectacles they haven't recurred since the surgery. She said that the spasms had previously occurred "at work after the stress of (spending) a day on the computer."

Furthermore, her friends noticed her improved posture. This improved posture drastically improved her symptoms of knotted neck and shoulder muscles.

Finding relief from Duane

This bilateral rectus recession procedure resulted in the elimination of the compensatory face turn, the obtainment of fusion in the primary position and the resolution of asthenopic symptoms. This case demonstrates that when a patient who has Duane's Retraction Syndrome must adopt a compensatory head posture to maintain binocular vision, we must consider surgery. Achieving the goal of obtaining binocular vision in the primary position will have a significant impact on the quality of a patient's life.

References available on request

Dr. Prince is an instructor at Wilmer Eye Institute at the Johns Hopkins Bayview Medical Center in Baltimore. You can reach him at jprince4@jhmi.edu.