Bilateral Inferior Rectus Research Articles

Eye muscle surgery.

In the past year experimental studies have analyzed the ease with which specific sutures can be adjusted, have investigated ways to prevent adhesions in animal models, and have studied variations of the inferior oblique at the surgical capture site. Our knowledge of rectus extraocular muscle pulleys continues to improve, and the value of botulinum toxin type A in the treatment of several conditions has been further documented. New surgical techniques include slanted recessions of the lateral rectus muscles, combined monocular resection and bilateral anterior transposition of the inferior oblique, and intraoperative use of acetylcholine during inferior oblique myectomy. Favorable results have been reported after clinically important modifications to the superior oblique muscle silicone expander and anterior transposition of the inferior oblique procedures, as well as after bilateral inferior rectus muscle recession in dysthyroid ophthalmopathy. Conjunctival inclusion cysts, anterior segment ischemia despite microvascular dissection, and corneal topographic changes are reported as complications occurring after strabismus surgery. Recent publications discussing these issues are reviewed here.

Bilateral inferior rectus muscle recession for correction of hypotropia in dysthyroid ophthalmopathy

Purpose: The restrictive myopathy of dysthyroid ophthalmopathy frequently results in strabismus and diplopia. The most common deviation is hypotropia. Ipsilateral inferior rectus muscle recession, the generally accepted treatment, may lead to a progressive marked overcorrection. The purpose of this study is to evaluate the results of bilateral asymmetric inferior rectus muscle operations with regard to late progressive overcorrection. Methods: A retrospective review of all patients undergoing bilateral inferior rectus muscle recession for dysthyroid ophthalmopathy between 1993 and 1997 found 8 patients with hypotropia resulting from dysthyroid ophthalmopathy. Alignment and motility were assessed preoperatively and postoperatively in all patients. Bilateral asymmetric inferior rectus muscle recession was performed on all patients with an adjustable suture performed on the hypotropic eye. A successful, long-term, postoperative result was defined as orthophoria or a vertical misalignment of less than or equal to 5 PD in primary gaze. Results: Data were collected from 8 patients at 4 to 6 weeks postoperatively. Six patients had successful alignment, and 2 patients remained undercorrected. Seven patients were successfully aligned, and 1 patient was undercorrected at the latest postoperative examination (mean, 18 months). Conclusion: In our series, bilateral asymmetric inferior rectus muscle recession resulted in successful correction of hypotropia without late postoperative overcorrections in patients with dysthyroid ophthalmopathy. (J AAPOS 1999;3:157-9)

Diagnosis and surgical management of strabismus associated with thyroid-related orbitopathy.

In the healing phase of thyroid-related orbitopathy, fibrosis and contracture of the extraocular muscles may result in restrictive ocular motility. Ocular misalignment may occur in both eyes and along three different axes of rotation. Successful surgical treatment depends on precise identification of the muscles that are restricting motility and producing the misalignment. Between 1980 and 1994, 22 patients were surgically treated for restrictive strabismus caused by thyroid-related orbitopathy. Preoperatively, all patients underwent complete neuroophthalmic, oculoplastic, and orthoptic examinations. Analysis of ductions, measurement of torsion, and the use of monocular neutralization techniques were essential additions to the usual motility exam. Patients were placed into diagnostic categories based on the clinical pattern of extraocular muscle restriction. Adjustable recessions were done for all initial surgeries. Patients with unilateral inferior rectus involvement or with ipsilateral inferior rectus-contralateral superior rectus involvement had large vertical deviations (equal to or > 20 prism diopters [delta]). Patients with bilateral inferior rectus involvement had small vertical deviations (< 20 delta). Excyclotorsion correlated strongly with the presence of tight inferior recti. Vertical comitance (upgaze versus downgaze measurement of equal to or < 15 delta) correlated with the ipsilateral inferior rectus-contralateral superior rectus pattern of involvement. Vertical incomitance (upgaze versus downgaze measurement of > 15 delta) correlated with unilateral inferior rectus involvement. Eighteen of 22 patients had excellent postoperative alignment and elimination of diplopia in functional positions of gaze. Those with less favorable results developed reversal of the hypertropia and exotropia in downgaze. Sixteen out of 19 patients who underwent inferior rectus recession had induced inferior eyelid retraction. Different combinations of extraocular muscle restriction in this series of patients produced characteristic patterns of misalignment. Appropriate, adjustable, strabismus surgery was successful in restoring binocular vision in 21 out of 22 patients with a minimum of complications.

5-Fluorouracil reduces scarring after strabismus surgery.

To examine the effect of topically administered 5-fluorouracil during strabismus surgery on post-operative scarring and the strength of the tendon-muscle union. Bilateral superior and inferior rectus muscle recessions were performed on 10 Stauffland white rabbits. The operated muscles in one eye received a 5-min topical application of 50 mg/mL solution of 5-fluorouracil (5-FU). The fellow eye received placebo treatment with a 5-min application of balanced sterile saline. Both eyes were enucleated 29 days postoperatively and examined for evidence of scarring. The tensile strength of both treated and untreated muscles was measured. Two additional rabbits received no surgery but had their eyes enucleated to serve as controls for tensile strength measurements. A significant reduction (P = 0.0001) in the amount of scarring was noted in eyes treated with 5-FU. A reduction in the tensile strength of both operated groups compared with the unoperated groups (P = 2.72 x 10(-12)) was noted, with a small but significant difference between the two operated groups (P = 0.0423). This study suggests that 5-FU may be a useful adjunctive therapy in strabismus surgery, especially when extensive postoperative scarring is expected.

Management of Diplopia Limited to Down Gaze

Objective: To evaluate the usefulness of various optical and surgical treatment modalities in the treatment of patients who were symptom free in the primary position of gaze yet had symptomatic diplopia in the reading position (down gaze at near). Patients and Methods: A retrospective chart review was conducted to identify all patients with presbyopia I have treated who were symptom free in the primary position but had diplopia in down gaze associated with vertically incomitant strabismus. Of 51 patients identified, 32 were symptomatic in down gaze due to a hypertropia associated with a unilateral inferior rectus muscle underaction. Twenty-two of these patients had previously undergone recession of the affected inferior rectus muscle for treatment of thyroid eye disease; four patients, for correction of entrapment secondary to blow-out orbital fracture; and four patients, for treatment of superior oblique muscle palsy. Two patients had undergone prior surgery for superior oblique myokymia. Eight patients had horizontal diplopia associated with anApattern, and eight patients had horizontal diplopia associated with aVpattern. Three patients had vertical and horizontal diplopia after partial recovery from third-nerve palsy. Results: The treatment modalities were varied and individualized. Treatment consisted of optical management (20 patients), surgical management (21 patients), or a combination of both (10 patients). These treatment modalities resulted in comfortable single binocular vision for reading in 41 of the 51 patients. Successful optical treatment consisted of Fresnel prisms (four patients), slab-off prisms (two patients), single-vision readers (seven patients), switch to nonprogressive bifocal lenses (three patients), and a high bifocal segment (16 patients). Successful surgical modalities included posterior fixation of the contralateral inferior rectus muscle (10 patients), surgery forA- orV-pattern strabismus (five patients), or bilateral inferior rectus muscle recession (six patients). Conclusion: Diplopia in the reading position frequently can be alleviated with a systematic approach that includes both optical and surgical modalities.

Management of diplopia limited to down gaze.

To evaluate the usefulness of various optical and surgical treatment modalities in the treatment of patients who were symptom free in the primary position of gaze yet had symptomatic diplopia in the reading position (down gaze at near). A retrospective chart review was conducted to identify all patients with presbyopia I have treated who were symptom free in the primary position but had diplopia in down gaze associated with vertically incomitant strabismus. Of 51 patients identified, 32 were symptomatic in down gaze due to a hypertropia associated with a unilateral inferior rectus muscle underaction. Twenty-two of these patients had previously undergone recession of the affected inferior rectus muscle for treatment of thyroid eye disease; four patients, for correction of entrapment secondary to blow-out orbital fracture; and four patients, for treatment of superior oblique muscle palsy. Two patients had undergone prior surgery for superior oblique myokymia. Eight patients had horizontal diplopia associated with an A pattern, and eight patients had horizontal diplopia associated with a V pattern. Three patients had vertical and horizontal diplopia after partial recovery from third-nerve palsy. The treatment modalities were varied and individualized. Treatment consisted of optical management (20 patients), surgical management (21 patients), or a combination of both (10 patients). These treatment modalities resulted in comfortable single binocular vision for reading in 41 of the 51 patients. Successful optical treatment consisted of Fresnel prisms (four patients), slab-off prisms (two patients), single-vision readers (seven patients), switch to nonprogressive bifocal lenses (three patients), and a high bifocal segment (16 patients). Successful surgical modalities included posterior fixation of the contralateral inferior rectus muscle (10 patients), surgery for A- or V- pattern strabismus (five patients), or bilateral inferior rectus muscle recession (six patients). Diplopia in the reading position frequently can be alleviated with a systematic approach that includes both optical and surgical modalities.

Horizontal canal input to cat extraocular motoneurons

Synaptic potential were recorded in identified extraocular motoneurons in the anesthetized cat, following stimulation of the horizontal canal nerve (HCN). Weak stimulation of the HCN evoked disynaptic EPSPs in ipsilateral medial rectus (i-MR), contralateral lateral rectus (c-LR) and disynaptic IPSPs in i-LR motoneurons. Weak stimulation of the HCN produced longer latency IPSPs (probably trisynaptic) in c-MR motoneurons. It is suggested that the HCN projects to an excitatory interneuron in the vestibular nucleus whose axon in turn projects to a third order inhibitory interneuron in the IIIrd nucleus which finally projects to c-MR motoneurons. Essentially there is no influence of the HCN stimulation on bilateral superior rectus (SR), inferior rectus (IR), superior oblique (SO) and inferior oblique (IO) motoneurons.