Morphological Differences in the Inferior Oblique Muscles from Subjects with Over-elevation in Adduction

The influence of orbital architecture on strabismus in craniosynostosis

PURPOSE

To better characterize the correlation of bony orbital dysmorphology with strabismus in craniosynostosis.

METHODS

The medical records of patients with craniosynostosis with and without strabismus seen at Rady Children's Hospital (San Diego, CA) from March 2020 to January 2022 were reviewed retrospectively in this masked, case-control study. Computed tomography scans of the orbits were analyzed to obtain dimensions of the orbital entrance and orbital cone. Primary outcome was correlation of strabismus with orbital measurements.

RESULTS

A total of 30 orbits from 15 patients with strabismus and 15 controls were included. Craniofacial disorders included in the study were nonsyndromic craniosynostosis (63%), Crouzon syndrome (13%), Apert syndrome (13%), and Pfeiffer syndrome (10%). Orbital index (height:width ratio) (P = 0.01) and medial orbital wall angle (P = 0.04) were found to differ significantly between the strabismus and control groups.

CONCLUSIONS

In our small cohort, bony orbital dimensions, including the ratio of orbital height to width and bowing of the medial orbital wall, were associated with strabismus in craniosynostosis.

Outcomes of inferior oblique myectomy versus recession combined with lateral rectus recession in V-pattern exotropias

PURPOSE

To compare outcomes of bilateral lateral rectus recession (BLRc) paired with either bilateral inferior oblique myectomy (BIOm) or bilateral inferior oblique recession (BIOc) to correct V-pattern exotropia.

METHODS

The medical records of children (≤18 years) who underwent BLRc with BIOm or BIOc (10 mm) for V-pattern intermittent exotropia between December 2020 and May 2022 and who had at least 6 months' postoperative follow-up were reviewed. Outcomes included horizontal alignment, bilateral inferior oblique action, stereopsis, postoperative exotropia control score, and additional strabismus surgeries. Analysis was stratified by preoperative V pattern into subgroups of 10Δ-14Δ and ≥15Δ.

RESULTS

Fifty patients underwent BLRc with BIOm (n = 26) or BIOc (n = 24), with no difference in age, sex, or follow-up length. Preoperatively, there were no differences in stereopsis, horizontal or vertical deviations in primary position, strabismus control, or inferior oblique overaction (IOOA). The BIOc group had greater preoperative V pattern than the BIOm group (18.1 ± 6.8 D vs 14.3 ± 7.0 D, resp. [P = 0.03]). There was no difference in BLRc surgical dose. At final follow-up (mean, 448 ± 189 days), both groups showed a postoperative decrease in horizontal deviation, amount of V pattern, and IOOA. For patients with ≥15Δ V pattern, BIOm decreased V pattern amount at distance (P = 0.02) and IOOA (P = 0.0035) more than BIOc, and BIOm patients had better control of residual strabismus at distance (P = 0.03) compared with the BIOc group overall, as well as for both V pattern subgroups. Two patients with BIOm and one with BIOc underwent additional strabismus surgery.

CONCLUSIONS

BIOm or BIOc in combination with BLRc decreased the angle of exotropia and improved control. However, BIOm, especially with large V patterns, had a greater effect on decreasing the V pattern and IOOA and showed better control of residual strabismus.

Spontaneous Recovery of Inferior Oblique Overaction in Three Saudi Children: A Case Report

The inferior oblique muscle overaction (IOOA) results in eye elevation on adduction, head tilt, difficulty in reading/writing, and changing ocular alignments in different gazes. Surgical correction is the management. We present two cases of bilateral and one case of unilateral IOOA that resolved spontaneously, and surgery differed. There was no IOOA six months after diagnosis. A sustained resolution IOOA following correction of hyperopia, improvement of vision, and esotropia correction possibly leading to rebalancing and maturing of extraocular muscles. Ophthalmologists should refer all IOOA cases to strabismologists, should not hurry to operate, counsel parents, and monitor a child's ocular movements.

Differences in Inferior Oblique Muscle Satellite Cell Populations between Primary and Secondary Inferior Oblique Muscle Overaction

INTRODUCTION

The aim of the study was to compare the number of paired box 7 (PAX7)-positive, myogenic differentiation 1 (MyoD1)-positive, and neural cell adhesion molecule-1 (NCAM)-positive satellite cells in human primary versus secondary inferior oblique muscle overaction (IOOA).

METHODS

This prospective observational study enrolled patients who underwent inferior oblique muscle myectomy at the Department of Pediatric Ophthalmology and Strabismus in Tianjin Eye Hospital between January 2020 and November 2020. The muscle specimens were processed. Immunohistochemistry and immunofluorescence were used to quantify inferior oblique muscle fiber diameter and PAX7-positive, NCAM-positive, and MyoD1-positive satellite cells.

RESULTS

Thirty-eight patients with inferior oblique overaction were enrolled: 18 with primary IOOA and 20 with secondary IOOA. The participants were significantly younger in the secondary IOOA group than in the primary IOOA group (2.8 ± 1.2 vs. 9.0 ± 3.2 years, p < 0.001). The muscle fiber diameter between the two groups was not significantly different (13.5 ± 1.4 vs. 13.8 ± 0.7 µm, p = 0.530), but PAX7+ (3.3 ± 2.8 vs. 1.8 ± 0.6, p < 0.001), NCAM+ (3.6 ± 1.5 vs. 1.7 ± 0.2, p < 0.001), and MyoD1+ (4.8 ± 1.9 vs. 2.7 ± 0.5, p < 0.001) cell counts were higher in primary IOOA than in secondary IOOA.

CONCLUSIONS

PAX7pos, MyoD-1pos, and NCAMpos cell counts per laminar nucleus were almost 2-fold higher in the primary IOOA group than in the secondary IOOA group.

Effect of Fibroblast Growth Factor 2 on Extraocular Muscle Structure and Function

Purpose

Mutations in the fibroblast growth factor (FGF) receptor can result in strabismus, but little is known about how FGFs affect extraocular muscle structure and function. These were assessed after short-term and long-term exposure to exogenously applied FGF2 to determine the effect of enhanced signaling.

Methods

One superior rectus muscle of adult rabbits received either a series of three injections of 500 ng, 1 µg, or 5 µg FGF2 and examined after 1 week, or received sustained treatment with FGF2 and examined after 1, 2, or 3 months. Muscles were assessed for alterations in force generation, myofiber size, and satellite cell number after each treatment.

Results

One week after the 5 µg FGF2 injections, treated muscles showed significantly increased force generation compared with naïve controls, which correlated with increased myofiber cross-sectional areas and Pax7-positive satellite cells. In contrast, 3 months of sustained FGF2 treatment resulted in decreased force generation, which correlated with decreased myofiber size and decreased satellite cells compared with naïve control and the untreated contralateral side.

Conclusions

FGF2 had distinctly different effects when short-term and long-term treatments were compared. The decreased size and ability to generate force correlated with decreased myofiber areas seen in individuals with Apert syndrome, where there is sustained activation of FGF signaling. Knowing more about signaling pathways critical for extraocular muscle function, development, and disease will pave the way for improved treatment options for strabismus patients with FGF abnormalities in craniofacial disease, which also may be applicable to other strabismus patients.