Visualization of Sliding and Deformation of Orbital Fat During Eye Rotation

Body Mass Index Is Associated With Orbital Pulley Degeneration Syndrome, Including Sagging Eye Syndrome

PURPOSE

Sagging eye syndrome (SES), esotropia with high myopia including heavy eye syndrome, and age-related esotropia (ARE)-collectively termed orbital pulley degeneration syndrome (OPDS)-are characterized by strabismus with orbital pulley lateral rectus-superior rectus band impairment. Herein, we examined body mass index (BMI) in OPDS to determine SES-associated anthropometric characteristics.

DESIGN

Retrospective cohort study.

METHODS

We compiled and analyzed the BMI of patients aged ≥50 years who underwent strabismus surgery at a single center in Shizuoka, Japan, between July 2020 and March 2023. BMI (kg/m2) was categorized into 4 groups: <18.5, 18.5 to 21.9, 22 to 24.9, and ≥25. As the boundary between OPDS and SES is ambiguous, we assumed a pure SES group by excluding patients with ARE and esotropia with high myopia from the OPDS group. Overall, 204 patients (age: 67.7 ± 9.7 years) were included in the study.

RESULTS

There were 78/126 and 49/119 patients in the OPDS/non-OPDS and SES/non-SES groups (age: 70.4 ± 9.5/66.0 ± 9.6 years, P = .002 and 75.0 ± 6.0/66.6 ± 9.5 years, P < .001; BMI: 21.2 ± 3.3/23.2 ± 3.0 kg/m2, P < .001 and 21.2 ± 3.3/23.1 ± 3.0 kg/m2, P = .003), respectively. In the BMI-stratified analysis, OPDS and SES were more prevalent in the <18.5 BMI group than in the 22 to 24.9 and ≥25 BMI groups (P < .001 and P = .006, respectively). Logistic regression analysis, adjusted for age and sex, showed that lower BMI was associated with a higher prevalence of OPDS and SES.

CONCLUSIONS

Patients with OPDS, including SES, had lower BMI than other patients with strabismus. Therefore, BMI may be a clinical clue to SES.

Magnetic Resonance Imaging of Globe Translation in Abducens Palsy

PURPOSE

It has been supposed that rectus muscle paralysis would cause proptosis due to the reduction in active posterior tension. This study aimed to test this proposition by evaluating globe translation during horizontal duction in patients with abducens palsy.

DESIGN

Prospective, single-center, fellow-eye controlled, case series.

METHODS

Horizontal globe rotation and translation were quantified using orbital magnetic resonance imaging of patients with isolated unilateral abducens nerve palsy without other ocular motility disorders. Unaffected fellow eyes served as the control group. Digital image analysis was performed.

RESULTS

The study included 5 female and 2 male patients with a mean ± standard deviation age of 52 ± 15 years. The average esotropia was 39.0 ± 9.6 diopters. Mean adduction was similar at 54.9 ± 10.4° in palsied eyes and 52.0 ± 7.1° in fellow eyes. However, abduction in palsied eyes was significantly less at 11.4 ± 7.1° than 37.1 ± 11.4° in fellow eyes (P = .0023). Average anterior translation in adduction was 0.46 ± 0.42 mm in palsied orbits, similar to 0.35 ± 0.47 mm in fellow orbits (P = .90). Anterior translation in abduction averaged 0.17 ± 0.53 mm in palsied orbits, similar to 0.27 ± 0.73 mm in fellow orbits (P = .80). Average medial translation in adduction at 0.32 ± 0.23 mm in palsied orbits was statistically similar to 0.12 ± 0.44 mm in fellow orbits (P = .54). Average lateral translation in abduction at 0.19 ± 0.18 mm in palsied orbits was similar to 0.33 ± 0.15 mm in control orbits (P = .38).

CONCLUSION

Abducens palsy does not alter normal eye translation during horizontal duction.

Opto-mechanical self-adjustment model of the human eye

The eye has specific optical and biomechanical properties that jointly regulate the eye's quality of vision, shape, and elasticity. These two characteristics are interdependent and correlated. Contrary to most currently available computational models of the human eye that only focus on biomechanical or optical aspects, the current study explores the inter-relationships between biomechanics, structure, and optical properties. Possible combinations of mechanical properties, boundary conditions, and biometrics were specified to ensure the opto-mechanical (OM) integrity to compensate for physiological changes in intraocular pressure (IOP) without compromising image acuity. This study evaluated the quality of the vision by analyzing the minimum spot diameters formed on the retina and drew how the self-adjustment mechanism affects the eye globe shape by adopting a finite element (FE) model of the eyeball. The model was verified by a water drinking test with biometric measurement (OCT Revo NX, Optopol) and tonometry (Corvis ST, Oculus).

Distinctive Features of Orbital Adipose Tissue (OAT) in Graves' Orbitopathy

Depot specific expansion of orbital-adipose-tissue (OAT) in Graves' Orbitopathy (GO) is associated with lipid metabolism signaling defects. We hypothesize that the unique adipocyte biology of OAT facilitates its expansion in GO. A comprehensive comparison of OAT and white-adipose-tissue (WAT) was performed by light/electron-microscopy, lipidomic and transcriptional analysis using ex vivo WAT, healthy OAT (OAT-H) and OAT from GO (OAT-GO). OAT-H/OAT-GO have a single lipid-vacuole and low mitochondrial number. Lower lipolytic activity and smaller adipocytes of OAT-H/OAT-GO, accompanied by similar essential linoleic fatty acid (FA) and (low) FA synthesis to WAT, revealed a hyperplastic OAT expansion through external FA-uptake via abundant SLC27A6 (FA-transporter) expression. Mitochondrial dysfunction of OAT in GO was apparent, as evidenced by the increased mRNA expression of uncoupling protein 1 (UCP1) and mitofusin-2 (MFN2) in OAT-GO compared to OAT-H. Transcriptional profiles of OAT-H revealed high expression of Iroquois homeobox-family (IRX-3&5), and low expression in HOX-family/TBX5 (essential for WAT/BAT (brown-adipose-tissue)/BRITE (BRown-in-whITE) development). We demonstrated unique features of OAT not presented in either WAT or BAT/BRITE. This study reveals that the pathologically enhanced FA-uptake driven hyperplastic expansion of OAT in GO is associated with a depot specific mechanism (the SLC27A6 FA-transporter) and mitochondrial dysfunction. We uncovered that OAT functions as a distinctive fat depot, providing novel insights into adipocyte biology and the pathological development of OAT expansion in GO.

Dynamic Imaging of the Eye, Optic Nerve, and Extraocular Muscles With Golden Angle Radial MRI

Purpose

The eye and its accessory structures, the optic nerve and the extraocular muscles, form a complex dynamic system. In vivo magnetic resonance imaging (MRI) of this system in motion can have substantial benefits in understanding oculomotor functioning in health and disease, but has been restricted to date to imaging of static gazes only. The purpose of this work was to develop a technique to image the eye and its accessory visual structures in motion.

Methods

Dynamic imaging of the eye was developed on a 3-Tesla MRI scanner, based on a golden angle radial sequence that allows freely selectable frame-rate and temporal-span image reconstructions from the same acquired data set. Retrospective image reconstructions at a chosen frame rate of 57 ms per image yielded high-quality in vivo movies of various eye motion tasks performed in the scanner. Motion analysis was performed for a left-right version task where motion paths, lengths, and strains/globe angle of the medial and lateral extraocular muscles and the optic nerves were estimated.

Results

Offline image reconstructions resulted in dynamic images of bilateral visual structures of healthy adults in only ∼15-s imaging time. Qualitative and quantitative analyses of the motion enabled estimation of trajectories, lengths, and strains on the optic nerves and extraocular muscles at very high frame rates of ∼18 frames/s.

Conclusions

This work presents an MRI technique that enables high-frame-rate dynamic imaging of the eyes and orbital structures. The presented sequence has the potential to be used in furthering the understanding of oculomotor mechanics in vivo, both in health and disease.