Medial Rectus Insertion Research Articles

Medial transposition of the lateral rectus muscle in experimentally induced medial rectus paralysis

When the oculomotor nerve is completely paralyzed, the affected eye shows severe outward displacement and poor cosmetic appearance. Past results of many surgical procedures for oculomotor palsy have been generally unsatisfactory. We tried a new surgical approach experimentally, in which the disinserted lateral rectus muscle was used as an adductor by medial transposition of the muscle. Five adult cats underwent disinsertion of the medial rectus muscle of both eyes to induce iatrogenic medial rectus paralysis. The disinserted medial rectus was removed as far back as possible to prevent reattachment. Then, the right lateral rectus muscle was disinserted and passed beneath the superior rectus muscle and resutured to the sclera 4mm superoposterior to the medial rectus insertion site. After excision of the bilateral medial rectus, a large exotropia of an average 47.6 delta (42.0-55.5 delta) was induced. The medial transposition of the right lateral rectus produced an average 36.6 delta (24.8-45.8 delta) correction of the exotropia. A satisfactory cosmetic result was achieved by this procedure.

The Medial Rectus Muscle Insertion Site in Infantile Esotropia

The distance from the corneoscleral limbus to the insertion site of the medial rectus muscle was measured at several stages of medial rectus recession surgery in 20 patients (40 eyes) with infantile esotropia. Disinsertion of the medial rectus muscle resulted in a mean reduction in the distance from the muscle insertion site to the corneoscleral limbus of 0.903 mm (P less than .001), whereas the use of fixation forceps on the insertion to abduct the eye resulted in an additional mean reduction of 0.306 mm (P less than .01). The strabismus surgeon often uses the muscle insertion site as a reference point in determining the desired location for recessing a muscle. Our results suggest that this method of measurement is unreliable in infantile esotropia because the position of the medial rectus muscle insertion site varies considerably during surgery.

Distance of muscle insertions in the corneal limbus

During the last 3 years (1983 to 1985) accurate measurements of the distance between rectus muscle insertions and the corneal limbus were made on strabismus patients during surgery. After dissection of a muscle the distance from the posterior limbus (gray-white line) to the insertion line of the muscle was measured with calipers both at the midpoint and at each end of the insertion. A limbal incision was employed without exception. Statistical analysis was performed on a personal computer, using the Lotus 1-2-3 program. In contrast to the traditionally popular values determined by Fuchs, which are already over 100 years old (in parentheses), we found the following mean values: medial rectus insertion 4.5 mm (5.5), in 675 eyes operated on; inferior rectus insertion 5.67 mm (6.5), in 22 eyes operated on; lateral rectus insertion 6.20 mm (6.9), in 493 eyes operated on; and superior rectus insertion 6.64 (7.7), in 21 eyes operated on. The reasons for these differences are discussed. Because of the large size of the samples for the horizontal muscles it was possible to narrow down the confidence limits for the true mean values considerably; however, it is clear from the great differences between the lowest and highest values observed that the distance from the muscle insertions to the corneal limbus varies widely.

Extraocular Muscle-Tendon Transfer with Scleral Augmentation

Two patients with 90 prism diopters of exotropia and an absent medial rectus muscle each had the nasal half of the superior and inferior rectus muscles joined with a thin strip of preserved sclera. The center of the scleral strip was first anchored to host sclera at the usual site of the medial rectus insertion. Alignment was improved in the primary position with a residual exodeviation of 25 prism diopters and 20 prism diopters, respectively. Each patient required secondary conjunctival recession because of a delle.