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Purpose: To verify whether central muscle sag actually induces excessive recession after recession of the rectus muscle in rabbit models., Methods: Twenty-four eyes of 12 rabbits were divided into two groups. In the right eyes (the muscle sagging group), half of the width of the original insertion was used to create a scleral suture during a 4-mm superior rectus muscle (SRM) recession and a central muscle sag of 2 mm was generated. Conventional 4-mm SRM recessions were performed in the left eyes (control group). At postoperative weeks 1, 2, and 4, the distances between the locations of the new insertion and the original insertion were measured at the center and nasal and temporal poles., Results: At postoperative week 4, the difference between the two groups at center was 1.38 ± 1.17 mm (P = .008). The mean extent of the recession at the nasal edge of the insertion was 5.21 ± 0.94 mm in the muscle sagging group, which showed posterior migration and slippage relative to the mean extent of the recession in the control group (4.29 ± 0.50 mm; P = .014). The mean extent of the recession at the temporal edge of the insertion was 5.50 ± 0.74 mm in the muscle sagging group and 4.50 ± 0.77 mm in the control group (P = .005)., Conclusions: Overcorrection that occurred in cases of central muscle sag in the rabbit models resulted from posterior migration of recessed muscle that occurred in conjunction with slippage of its nasal and temporal edges., (Copyright 2013, SLACK Incorporated.)

Background: Previous studies have indicated that axial length determination is important in strabismic patients for defining the limit for a safe maximum recession of the medial rectus. Also, the response to strabismus surgery may be, in part, a function of axial length. We previously published a formula for predicting axial length based on age and refractive error; however, its accuracy has not been tested in a patient population that is different from the one used to generate the formula. The purpose of this study is to test a formula for estimating axial length, given age and refractive error, in a population that is different from that from which it was generated., Method: We measured axial length using A-scan ultrasonography in 163 consecutive patients undergoing strabismus surgery. Twenty-nine patients were younger than 18 months of age; 134 patients were between 18 months and 10 years of age. We compared the measured axial length determination with the axial length value estimated by a formula generated from our previous published series., Results: For patients younger than 18 months of age, the equation estimated axial length within 0.5 mm in 41.4% of patients, within 1.0 mm in 79.3% of patients, and within 1.5 mm in 93.1% of patients. For patients between 18 months and 18 years of age, the formula estimated axial length within 0.5 mm in 37.3% of patients, within 1.0 mm in 73.1% of patients, and within 1.5 mm in 87.3% of patients., Conclusions: The formula may be useful for the strabismus surgeon in estimating axial length when A-scan ultrasonography is not available in an operating room setting, particularly in congenital esotropes who require larger recessions in small eyes. If, however, A-scan ultrasonography is available, it is preferable to using the formula. The formula is not sufficiently accurate for use for calculating intraocular lens power.

Background: Ocular motility dysfunction following strabismus surgery may be the result of postoperative scarring or the formation of adhesions. Mitomycin C (MMC) has been used with encouraging results as an adjunct to standard treatment of hypertrophic conjunctival scars after strabismus surgery. It has been demonstrated that MMC does not inhibit muscle reattachment and might inhibit adhesions and scar formation in the rabbit. We investigated in a rabbit model effectiveness of MMC in reducing the formation of postoperative adhesions following reoperations and the tensile strength of the new musculo-scleral junction., Methods: A prospective, masked-observer, controlled study was performed in rabbits. Symmetrical bilateral recessions of the superior and inferior rectus muscles were performed on each rabbit. A reoperation was performed 6 weeks later, in which the muscles were advanced back to their original insertion. During the reoperation, one eye served as the control while the other was treated with a 5-minute intraoperative exposure to topical mitomycin., Results: Mitomycin reduced the formation of adhesions and the amount of postoperative scarring. The tensile strength of the musculo-scleral junction was reduced in the mitomycin-treated eyes but exceeded the force generated during extraocular ductions., Conclusion: MMC may be an effective adjunctive therapy in the treatment of strabismus associated with pre-existing adhesions or scarring.

We have used a rabbit model to study insertion movement, rotational forces, disinsertion forces, and histology of the surgically created insertion site after recession of the inferior rectus (IR) using a conventional (CONV) or suspension (SUS) technique combined with an ipsilateral superior rectus (SR) resection. During the 5-week observation period, the CONV and SUS recessed IR showed an initial posterior movement followed by an anterior movement while all resected SR had an initial posterior movement which remained stable. SR rotational forces increased and IR remained constant throughout the 5-week observation period. There were no rotation force differences between the SUS and CONV recession techniques. Disinsertion forces showed an initial large decrease in force followed by a gradual increase to preoperative levels by 3 postoperative weeks. Disinsertion force differences between the CONV and SUS recessions were observed for 5 weeks after surgery. Histologic analysis showed a delayed inflammatory response on the SUS recession compared to the CONV recession and at the middle of the insertion compared to the poles which was minimized by 3 weeks after surgery.

A synthetic polypentapeptide sleeve was placed around the superior rectus muscle of five New Zealand white rabbits in hopes of preventing postoperative fibrous scarring. Two forms of the polypentapeptide were used. No significant inflammation or scarring occurred with either form of the polypentapeptide when compared to controls. One form elicited a fibrous membrane surrounding the sleeve within 2 weeks. The other elicited no such reaction after 2 months. The latter form of the polypentapeptide may be useful in preventing scarring following strabismus surgery.

In 581 strabismus operations, the distances between the limbus and the scleral insertions of the rectus muscles were measured, as well as the distances between the anterior end of the insertions of the superior and the inferior obliques and the temporal end of the insertion of the superior rectus and the inferior end of the one of the lateral rectus, respectively. In the case of the rectus muscles, smaller values than the classical ones were found. With the obliques, the measurements were similar to those of Fink. The differences with age or refraction were not statistically significant. We concluded that these parameters are not important in the determination of the amount of recession of an extraocular muscle in strabismus operations in patients over the age of six months.

Several different artifacts can induce errors in measurements obtained during strabismus surgery. Fixating the severed rectus muscle stump with forceps during strabismus surgery can result in a temporary anterior displacement of the insertion. This may result in inaccuracies in determining the site to which the muscle is to be recessed. This displacement was quantified in a prospective masked manner and was found in some patients to result in as much as 1 mm of error. It can be prevented by measuring the recession prior to fixating the insertion stump with forceps; however, it cannot always be prevented by measuring from the limbus, which also introduces other artifacts due to geometric principles. An "advancement effect" occurs during a rectus muscle recession due to the mechanics of suture placement in the muscle. It was quantified in a masked manner and found to be approximately .5 mm in most cases. A "V" shaped deformity of the insertion stump may occur immediately adjacent to the forceps. This deformity frequently distorts the insertion by as much as several millimeters.