Masaki Okano

Advancement of medial rectus muscle to the original insertion for consecutive exotropia

Twenty-four patients who underwent surgery to correct consecutive exotropia that developed iatrogenically after surgical overcorrection were studied retrospectively. All patients underwent single or bilateral advancement of the medial rectus muscle to the original muscle insertion. The mean preoperative exodeviation was 26.7 prism diopters at distance and 35.2 delta at near. Postoperatively, in cases receiving advancement of a single medial rectus, the mean amount of correction was 23.2 delta at distance and 29.6 delta at near. In cases receiving bilateral medial rectus advancement, the mean amount of postoperative correction was 26.3 delta at distance and 39.8 delta at near. Adduction deficiency was normalized in five patients (71%), while convergence insufficiency was improved in only nine patients (45%) after surgery. Twelve (50%) patients had binocular single vision at distance on a normal or abnormal basis as determined by the Bagolini lens test.

Preoperative prism correction in patients with acquired esotropia

We performed a prospective study of preoperative prism adaptation in 77 patients with acquired esotropia. Sixty-three of them increased their angle of squint when wearing Fresnel press-on prisms for 5–7 days. After the angle had stabilized to a point that did not exceed the press-on prisms by more than 10 prism D, they were randomly divided into two groups. Thirty-two patients underwent surgery based on the prism-adapted angle. The other 31 patients underwent surgery based on their initially measured angle. Fourteen patients who did not respond to prism correction underwent surgery based on the angle before prism correction. Success rates with deviations between 0 and 10 prism diopters measured 1 year after surgery were highest in those in whom surgery was based on the prism-determined angle and were lowest in the nonresponders, who had no fusion response to the prisms.

Strabismus Surgery in Ocular Myasthenia gravis

We evaluated the efficacy of eye muscle surgery in 4 patients with ocular myasthenia gravis with troublesome diplopia. All patients were in remission and had shown a consistently stable angle of deviation for at least 6 months preoperatively. The extent of eye muscle surgery was based on the degree of deviation in the primary position, and conventional recession and resection procedures were performed in 3 patients and hang-loose recession with an adjustable recession in 1. Single binocular vision was obtained in 3 patients in the primary position without prism correction or compensatory head posture. Electron-microscopic studies on the eye muscle specimens obtained at strabismus surgery revealed non-specific degenerative findings for the muscle fibers and sarcomeric disorganization compared to that in a control extraocular muscle.

Extraocular muscle surgery in a rabbit model: site of reattachment following hang-back and conventional recession.

To determine the precise site of reattachment of recessed muscles, 4-mm conventional and hang-back recessions of the inferior rectus muscle were performed in 18 albino rabbits. Six weeks later, the distance from the anterior border of the reattached muscle to the insertion was measured both grossly and microscopically. In all cases the operated muscles had advanced minimally from the site of surgical placement. Gross observation showed that the mean forward creep was significantly greater for those rabbits which underwent hang-back recession (1.81±0.67 mm) than for those that were submitted to the conventional technique (0.83±0.38 mm). Measurements done on histological sections revealed that the mean distance of the anterior border of the muscle fiber from the reference suture was larger for conventional recession (2.73±0.75 mm) than for hang-back recession (1.91±0.72 mm).

Critical Period for Restoration of Normal Stereoacuity in Acute-onset Comitant Esotropia

We conducted a retrospective study of 25 patients with acute-onset comitant esotropia to evaluate whether the timing of the start of treatment is a critical factor in the development of normal stereopsis. The mean age at onset was 12 years 4 months, and mean age at the start of treatment was 17 years 9 months. Bifixation was defined as a stereoacuity threshold score that was numerically lower than 60 seconds of arc on stereotesting. An operation was performed on the nonfixating eye for the prism-adapted angle. At the final examination, bifixation was observed in four patients (16%) with the Randot test and in 15 patients (60%) with the Titmus test. No relationship was found between the time of the start of treatment and the postoperative development of stereopsis, nor was there a significant (P > .10) difference between the two groups with early and delayed start of treatment in the proportion of patients with bifixation.

Morphological Changes in the Orbital Surface Layer Muscle of the Rabbit Eye Produced by Botulinum Toxin

We quantitated the morphological changes in the orbital surface layer muscles in the rabbit following the single injection of botulinum A toxin. Experiments were performed in 9 white rabbits (1.6–3.0 kg). They were administered 5 units (5 rabbits) or 10 units (4 rabbits) of botulinum toxin injected into the superior rectus muscle of one eye. The diameter of myofibers of the orbital and intermediate layer zones was measured with an ocular micrometer on histological sections 3 days and 1, 3 and 5 weeks after injection. Quantitative changes were noted in the muscle fibers of the orbital surface layer zone following the injection of 10 units of botulinum toxin. At 1 week, the diameter of myofibers in the orbital layer was reduced, but it was increased at 5 weeks compared to that in the control eyes; in contrast, no change in the diameter of muscle fibers was found in the intermediate layer zone.

Synoptometer Analysis of Vertical Shoot in Duane's Retraction Syndrome

Vertical deviation of the affected eye caused by horizontal change of gaze was measured with a synoptometer in 5 cases of Duanes retraction syndrome type III. Step-by-step measurement clearly showed two types of incomitance patterns, i.e. upshoot and up- and downshoot in adduction. The former suggests a paradoxical synergistic innervation between the medial rectus and superior rectus muscles, and the latter suggests an abnormal vertical movement of the lateral rectus muscle over the globe on elevation or depression of the eye. Recession of the lateral rectus muscle, however, reduced the vertical deviation regardless of the incomitance pattern.

Intraoperative suspension-recession technique for treatment of vertical strabismus in thyroid myopathy.

Ten patients underwent extraocular muscle surgery with an intraoperative suspension-recession technique for diplopia induced by vertical strabismus in thyroid myopathy. The average ratio of the reduction of vertical deviation to the amount of surgery was 1.8 degrees/mm (range, 1.0 degrees/mm-2.8 degrees/mm). Eight (80%) patients had single binocular vision restored in the primary position without prism or compensatory torticollis after surgery. One patient who showed evidence of abnormal thyroid function at surgery developed an overcorrection postoperatively.