Arthur L. Rosenbaum

Heterotopic Muscle Pulleys or Oblique Muscle Dysfunction

INTRODUCTION The description of connective tissue sleeves that function as pulleys for the rectus extraocular muscles (EOMs) suggests that abnormalities of EOM pulley position might provide a mechanical basis for some forms of incomitant strabismus. Pulleys determine the paths and thus the pulling directions of EOMs. METHODS High-resolution magnetic resonance images spanning the orbits were obtained in primary position, upgaze, and downgaze for each subject. Paths of the EOMs were measured with reference to the orbital center and permitted inference of pulley locations. RESULTS Data from 18 orbits of orthotropic subjects defined means and SDs of normal EOM pulley coordinates. Eight patients, aged 17 to 60 years, had heterotopic EOM pulleys, defined as displaced at least 2 SDs from normal. We found one to eight heterotopic pulleys (considering both orbits) in each of four patients who had been diagnosed with marked superior oblique (SO) overaction and mild to marked inferior oblique (IO) underaction. Each patient had superior mislocation of at least one lateral rectus pulley by 1.8 to 4.9 mm. Three patients diagnosed with mild to moderate IO overaction and mild to moderate SO underaction in only one orbit had one to three heterotopic EOM pulleys. Each of those patients had at least one lateral rectus pulley inferiorly dislocated by 1.9 to 4.9 mm. The final patient, who was diagnosed with mild IO underaction and normal SO function bilaterally, had bilateral superior mislocation of the medial rectus pulleys by greater than 2 mm. Computer simulations using the Orbit program (Eidactics, San Francisco) incorporating individually measured pulley positions reproduced the clinical patterns of incomitant strabismus in all cases without postulating abnormalities of oblique muscle innervation or contractility. CONCLUSION Heterotopic EOM pulleys can cause patterns of incomitant strabismus that have been attributed to oblique muscle dysfunction. Even isolated mislocations of less than 2 mm, coupled with smaller mislocations of the other pulleys, can produce the clinical appearance of bilateral oblique dysfunction. Pulley heterotopy should be considered in the differential diagnosis of incomitant strabismus and oblique dysfunction.

Distance stereoacuity. Assessing control in intermittent exotropia.

BACKGROUND A patients ability to control an intermittent exotropic deviation is usually assessed by subjective means such as observation of control in the office, questioning the patient and/or family about control at home, and reports of monocular eye closure in bright light. An objective method of assessing control has not been developed. PURPOSE The purposes of this study are to determine if distance stereoacuity was different in patients with intermittent exotropia than in normal subjects and to determine if distance stereoacuity could be used as a objective means of assessing control in intermittent exotropia. METHODS The authors evaluated near and distance stereoacuity in 44 patients with intermittent exotropia and 50 normal subjects. Patients with intermittent exotropia also were assessed for office control, home control, and monocular eye closure in bright light. Additionally, six patients who underwent successful surgery were reevaluated postoperatively. CONCLUSION Normal subjects and patients with intermittent exotropia had good near stereoacuity. Patients with intermittent exotropia demonstrated significantly worse distance stereoacuity than the population of normal subjects (P < 0.001). Five of six patients with poor distance stereoacuity preoperatively had dramatic improvement in distance stereoacuity postoperatively. Diminished distance stereoacuity seems to be an objective measure of poor control of the exotropic deviation. This test may provide important objective criteria for deciding when to perform surgery in patients with intermittent exotropia.

Loss of electroretinographic oscillatory potentials, optic atrophy, and dysplasia in congenital stationary night blindness

New criteria for diagnosing congenital stationary night blindness include loss of the oscillatory potentials in the photopic and bright-flash dark-adapted electroretinogram, and atrophy or dysplastic changes, or both, in the optic nerve head. Ten patients (seven male and three female, ranging in age from 6 to 19 years) had typical findings of congenital stationary night blindness including congenital nonprogressive nyctalopia, no pigmentary retinopathy, and full visual fields consistent with myopia. Visual acuities ranged from 20/30 to 20/60, though one patient had a visual acuity of 20/200. Most patients had histories of strabismus. The photopic electroretinograms were subnormal. Of the male patients, five had tilted optic disks with temporal portions of the nerve missing, and two had misshapen nerve heads. The three female patients had pallor of the optic disk without evidence of tilt.

Long-term results of the surgical management of intermittent exotropia

PURPOSE To examine long-term surgical success rates (>10 years) for patients with intermittent exotropia and the risk factors for failure of surgery in these patients. METHODS An attempt was made to contact all patients who underwent surgical treatment for intermittent exotropia between the years of 1970 to 1998 with a minimum postoperative follow-up of 10 years. Each patient underwent a detailed sensory and motor examination, including measurements of near and distance stereoacuity, cover testing, and ocular rotations. Patients were classified as achieving an excellent, fair, or poor outcome on the basis of motor and sensory outcomes. Risk factor analysis was performed to evaluate associations with a poor outcome and reoperations. RESULTS Of 197 patients identified, 50 were reevaluated. When combined motor/sensory criteria for surgical success were used, we found that 38% of patients achieved an excellent outcome, whereas 34% and 28% achieved a fair or poor outcome, respectively. When only the motor criteria were used, we found that 64% had an excellent outcome, whereas the remaining patients achieved either a fair (18%) or a poor (18%) outcome. During the follow-up period, 60% of patients required at least one reoperation. Multivariate risk factor analysis determined that anisometropia (p = 0.03) was associated with a poor outcome, whereas postoperative undercorrection (p = 0.04) and lateral incomitance (p = 0.06) were associated with reoperations. CONCLUSIONS Long-term surgical results in intermittent exotropia are less encouraging when sensory status is added to the evaluation. Patients with anisometropia, lateral incomitance, and immediate postoperative undercorrection are at increased risk for poor outcomes and to require reoperations.

Posterior fixation sutures: a revised mechanical explanation for the fadenoperation based on rectus extraocular muscle pulleys.

PURPOSE To determine the effect of the rectus extraocular muscle pulleys on the fadenoperation, an operation designed to fixate the posterior muscle belly to the underlying retroequatorial sclera. METHODS First, duction into the field of action of the operated-on muscle was quantified retrospectively after fadenoperation. Magnetic resonance imaging was then performed prospectively after surgery to verify anatomic changes. Forced duction testing was performed prospectively during surgery before and after faden placement. Finally, computed tomography in a cadaver containing radiographic markers was performed prospectively to determine the effect of fadenoperation on the position of the medial rectus insertion relative to its pulley. RESULTS Mean maximum adduction after medial rectus fadenoperation was 18 degrees (range, 10 to 25 degrees; 13 eyes). Fadenoperations combined with large medial rectus recessions restricted adduction more than fadenoperations combined with smaller recessions (P = .019), but even fadenoperations without recessions substantially restricted adduction. Mean maximum abduction after lateral rectus fadenoperation was 40 degrees (range, 25 to 45 degrees; four eyes). Axial magnetic resonance imaging in two eyes demonstrated a smaller loss of muscle tangency to the globe during contraction than predicted by geometric models. Forced ductions in nine patients performed immediately after faden placement demonstrated a new mechanical restriction to duction toward the operated-on muscle. Cadaveric computed tomographic scans demonstrated posterior displacement of the medial rectus pulley during adduction after fadenoperation. CONCLUSIONS Posterior fixation sutures do not significantly decrease muscle torque during contraction. Because posterior fixation sutures posteriorly displace the pulley sleeve during duction toward the operated-on muscle, the mechanical restriction after surgery probably represents the force deforming the pulley. This mechanical restriction may account for the limitation in duction seen after fadenoperation.

Quantitative Magnetic Resonance Morphometry of Extraocular Muscles: A New Diagnostic Tool in Paralytic Strabismus

Paralytic strabismus is often diagnostically ambiguous due to the similarity of patterns of misalignment produced by different mechanisms. To address this problem, we have developed a new technique employing high-resolution, surface coil magnetic resonance imaging to quantify extraocular muscle size and contractility. Adjacent coronal images are obtained spanning the anteroposterior extent of each orbit, and repeated in multiple directions of gaze. Contractility is evaluated from analysis of muscle cross-sectional areas. The quantitative size and contractile characteristics of normal rectus and superior oblique muscles are reviewed, along with the effects of superior oblique palsy. The morphometric features of lateral rectus palsy are illustrated by three clinical cases exhibiting deficient contractility and atrophy of the lateral rectus muscle. A case of superior oblique palsy is presented illustrating atrophy and lack of contractility of the involved superior oblique muscle. This imaging technique can be employed in any clinical center and permits insight into extraocular muscle function in complex strabismus cases.

Vertical Rectus Muscle Transposition Surgery for Duane's Syndrome

Thirteen patients with Duanes syndrome, Type I, underwent full vertical rectus muscle transposition. Prior to surgery, all patients had esotropia in the primary position and 11 patients had a face turn. Postoperatively, esotropia was improved in 77%. The face turn was improved in 100% and eliminated in 69%. Abduction ability was increased and binocular diplopia-free field size enlarged to a mean of 60 degrees. Seven patients (54%) with a mean preoperative deviation of 17 prism diopters required only vertical rectus muscle transposition to improve their face turn and strabismus. Six patients (46%) with a mean preoperative deviation of 30 delta required an additional medial rectus recession several months later. Two patients (15%) developed a vertical deviation following vertical rectus muscle transposition.

Distance stereo acuity improvement in intermittent exotropic patients following strabismus surgery. Discussion

To determine whether distance stereo acuity improved following strabismus surgery in patients with intermittent exotropia, we tested 20 patients (5 to 87 years old) preoperatively and postoperatively using the Mentor BVAT II Video acuity tester (Santa Barbara, Calif) and binocular visual system. Acuity improved in 75% as assessed by contour circles and in 45% as assessed by random dot E tests at distance. Our results suggest that surgical realignment of intermittent exotropia restores distance stereo acuity. We conclude that measuring distance stereo acuity offers valuable information in the evaluation of the intermittent exotropic patient.

Horizontal Transposition of the Vertical Rectus Muscles for Treatment of Ocular Torticollis

In most instances, a head tilt to either shoulder is caused by hypertropia or cyclotropia and responds well to conventional surgical strengthening or weakening operations on the cyclovertical muscles. Occasionally, an ocular head tilt occurs in the absence of cyclovertical strabismus, in association with congenital nystagmus or without an apparent cause. We have successfully treated four of five such patients by surgically rotating the eye(s) around the sagittal axis. This was accomplished by horizontal transposition of the vertical rectus muscles. No complications were encountered. We present this method as a viable alternative to other surgical approaches to rotate the eyes around their sagittal axis.

Cycloplegic Refraction in Esotropic Children: Cyclopentolate versus Atropine

Retinoscopy was performed on a population of predominantly white esotropic children younger than 5.5 years with cyclopentolate 1% and atropine 1.0%. Atropine 1.0% revealed +0.34 diopters more hyperopia than cyclopentolate 1.0%, when the mean differences between the two drugs were examined. Mean difference analysis would probably indicate that atropine retinoscopy was unnecessary. However, 22% of the children had +1.0 diopters or more of hyperopia uncovered by atropine. This significant subpopulation suggests that in young patients with esotropia, an atropine refraction is essential to uncover the maximum amount of hyperopia. Almost all of this subgroup with +1.00 or greater hyperopia had an initial cyclopentolate retinoscopy of +2.00 diopters or more. Therefore, retinoscopy using atropine cycloplegia becomes even more important in this population. There was a trend for the greater differences to be in children older than age 2 years. However, these values were not statistically significant.