Magnetic Resonance Imaging of the Globe-Tendon Interface for Extraocular Muscles: Is There an “Arc of Contact”?

Abstract

Contrary to the "arc of contact" biomechanical model, normal and postsurgical EOMs are significantly non-tangent to the globe at their scleral insertions. The "arc of contact" should be replaced in biomechanical modeling by the experimentally measured angles at tendon insertions. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Revisiting Posterior Fixation Sutures Surgery: Unveiling Novel Approaches for Primary Management of Diverse Esotropia Cases

“…The suggested principle has been to recess the MR bilaterally to correct for the distance esotropia and to use the PFS to correct for the convergence excess. However, the theoretical concept based on the arc of contact and shortening of the lever arm cannot fully explain how PFS alone can achieve good alignment in the primary gaze position [ 30 ]. Additionally, by axial magnetic resonance imaging, Clark et al demonstrated that significant change in extraocular muscle tangency with the globe does not occur after PFS of an extraocular muscle [ 31 ].…”

Revisiting Posterior Fixation Sutures Surgery: Unveiling Novel Approaches for Primary Management of Diverse Esotropia Cases

“…The suggested principle has been to recess the MR bilaterally to correct for the distance esotropia and to use the PFS to correct for the convergence excess. However, the theoretical concept based on the arc of contact and shortening of the lever arm cannot fully explain how PFS alone can achieve good alignment in the primary gaze position [ 30 ]. Additionally, by axial magnetic resonance imaging, Clark et al demonstrated that significant change in extraocular muscle tangency with the globe does not occur after PFS of an extraocular muscle [ 31 ].…”

MR-Eye: High-Resolution Microscopy Coil MRI for the Assessment of the Orbit and Periorbital Structures, Part 2: Clinical Applications

“…Cross-sectional imaging is already in use for orbital abnormalities, 27,36 and MC-MR imaging of the orbits has been previously described but with rather limited clinical application. 2,[42][43][44] However, the high spatial resolution of MC-MR imaging facilitates assessment of lesions and their relationship to normal anatomic structures in detail sufficient to more confidently and accurately guide the therapeutic approach. MC-MR imaging is particularly valuable for depicting tumor invasion of critical small structures such as the tarsal plates and for depicting clean fat planes between important structures or obliteration of these planes due to tumor invasion.…”

Functional anatomy of the orbit in strabismus surgery: Connective tissues, pulleys, and the modern surgical implications of the “arc of contact” paradigm

“…Consider the pulley as the muscle's functional starting point or "origin" (Demer et al, 1995(Demer et al, , 2000. Any recession will permanently modify the torque vector at the globe's surface, decreasing the torque for a given muscle innervation level (Clark & Demer, 2018).…”

“…In light of the discovery of muscle pulleys, these models need reevaluation and reinterpretation. The non‐linear paths resulting from these pulleys provide a more dynamic and intricate understanding of eye movement (Clark et al., 1999 ; Clark & Demer, 2018 ; Demer, 2003 , 2004 , 2006b ; Demer et al., 1995 , 2000 ; Miller, 1989 , 2007 ).…”

“…Recent MRI studies demonstrated that contrary to the arc of contact biomechanical model, standard and postsurgical EOMs are significantly nontangent to the globe during large ipsiversive ductions (Figure 4 ). In most cases, the EOM tendon thickness and post‐insertional curvilinear path combined to create a substantially larger‐than‐predicted angle at tendon insertion with resultant greater‐than‐predicted loss of globe tangency (Clark et al., 1999 ; Clark & Demer, 2018 ).…”

Revisiting Posterior Fixation Sutures Surgery: Unveiling Novel Approaches for Primary Management of Diverse Esotropia Cases

“…The suggested principle has been to recess the MR bilaterally to correct for the distance esotropia and to use the PFS to correct for the convergence excess. However, the theoretical concept based on the arc of contact and shortening of the lever arm cannot fully explain how PFS alone can achieve good alignment in the primary gaze position [ 30 ]. Additionally, by axial magnetic resonance imaging, Clark et al demonstrated that significant change in extraocular muscle tangency with the globe does not occur after PFS of an extraocular muscle [ 31 ].…”

MR-Eye: High-Resolution Microscopy Coil MRI for the Assessment of the Orbit and Periorbital Structures, Part 2: Clinical Applications

“…Cross-sectional imaging is already in use for orbital abnormalities, 27,36 and MC-MR imaging of the orbits has been previously described but with rather limited clinical application. 2,[42][43][44] However, the high spatial resolution of MC-MR imaging facilitates assessment of lesions and their relationship to normal anatomic structures in detail sufficient to more confidently and accurately guide the therapeutic approach. MC-MR imaging is particularly valuable for depicting tumor invasion of critical small structures such as the tarsal plates and for depicting clean fat planes between important structures or obliteration of these planes due to tumor invasion.…”

Functional anatomy of the orbit in strabismus surgery: Connective tissues, pulleys, and the modern surgical implications of the “arc of contact” paradigm

“…Consider the pulley as the muscle's functional starting point or "origin" (Demer et al, 1995(Demer et al, , 2000. Any recession will permanently modify the torque vector at the globe's surface, decreasing the torque for a given muscle innervation level (Clark & Demer, 2018).…”

“…In light of the discovery of muscle pulleys, these models need reevaluation and reinterpretation. The non‐linear paths resulting from these pulleys provide a more dynamic and intricate understanding of eye movement (Clark et al., 1999 ; Clark & Demer, 2018 ; Demer, 2003 , 2004 , 2006b ; Demer et al., 1995 , 2000 ; Miller, 1989 , 2007 ).…”

“…Recent MRI studies demonstrated that contrary to the arc of contact biomechanical model, standard and postsurgical EOMs are significantly nontangent to the globe during large ipsiversive ductions (Figure 4 ). In most cases, the EOM tendon thickness and post‐insertional curvilinear path combined to create a substantially larger‐than‐predicted angle at tendon insertion with resultant greater‐than‐predicted loss of globe tangency (Clark et al., 1999 ; Clark & Demer, 2018 ).…”

Revisiting Posterior Fixation Sutures Surgery: Unveiling Novel Approaches for Primary Management of Diverse Esotropia Cases

“…The suggested principle has been to recess the MR bilaterally to correct for the distance esotropia and to use the PFS to correct for the convergence excess. However, the theoretical concept based on the arc of contact and shortening of the lever arm cannot fully explain how PFS alone can achieve good alignment in the primary gaze position [ 30 ]. Additionally, by axial magnetic resonance imaging, Clark et al demonstrated that significant change in extraocular muscle tangency with the globe does not occur after PFS of an extraocular muscle [ 31 ].…”

MR-Eye: High-Resolution Microscopy Coil MRI for the Assessment of the Orbit and Periorbital Structures, Part 2: Clinical Applications

“…Cross-sectional imaging is already in use for orbital abnormalities, 27,36 and MC-MR imaging of the orbits has been previously described but with rather limited clinical application. 2,[42][43][44] However, the high spatial resolution of MC-MR imaging facilitates assessment of lesions and their relationship to normal anatomic structures in detail sufficient to more confidently and accurately guide the therapeutic approach. MC-MR imaging is particularly valuable for depicting tumor invasion of critical small structures such as the tarsal plates and for depicting clean fat planes between important structures or obliteration of these planes due to tumor invasion.…”

Functional anatomy of the orbit in strabismus surgery: Connective tissues, pulleys, and the modern surgical implications of the “arc of contact” paradigm

“…Consider the pulley as the muscle's functional starting point or "origin" (Demer et al, 1995(Demer et al, , 2000. Any recession will permanently modify the torque vector at the globe's surface, decreasing the torque for a given muscle innervation level (Clark & Demer, 2018).…”

“…In light of the discovery of muscle pulleys, these models need reevaluation and reinterpretation. The non‐linear paths resulting from these pulleys provide a more dynamic and intricate understanding of eye movement (Clark et al., 1999 ; Clark & Demer, 2018 ; Demer, 2003 , 2004 , 2006b ; Demer et al., 1995 , 2000 ; Miller, 1989 , 2007 ).…”

“…Recent MRI studies demonstrated that contrary to the arc of contact biomechanical model, standard and postsurgical EOMs are significantly nontangent to the globe during large ipsiversive ductions (Figure 4 ). In most cases, the EOM tendon thickness and post‐insertional curvilinear path combined to create a substantially larger‐than‐predicted angle at tendon insertion with resultant greater‐than‐predicted loss of globe tangency (Clark et al., 1999 ; Clark & Demer, 2018 ).…”