Extraocular connective tissues: a role in human eye movements?

Area of Science:

• Ophthalmology and Anatomy
• Connective tissue research
• Musculoskeletal system

Background:

• Previous MRI studies hypothesized specific connective tissues couple extraocular muscles (EOMs) to the pulley system.
• The precise anatomical structure and function of orbital connective tissues surrounding human EOMs remain incompletely understood.
• The active pulley hypothesis (APH) relies on specific interpretations of EOM attachments.

Purpose of the Study:

• To conduct a detailed anatomic analysis of the connective tissues surrounding human horizontal EOMs.
• To specifically investigate the orbital connective tissues previously assumed to couple EOMs to the pulley.
• To clarify the anatomical basis for observed findings in MRI studies.

Main Methods:

• Preparation of serial 5-micrometer sections from paraffin-embedded human lateral and medial rectus muscles and surrounding tissues.
• Masson's trichrome staining for light microscopic examination.
• Distinguishing muscle fibers (red) from connective tissues (blue) to analyze their structural relationships.

Main Results:

• Orbital connective tissues form a collagenous bridge, identified as the check ligament (CL), between the distal EOM and orbital periosteum.
• The CL invests orbital muscle fibers, maintaining their alignment, and forms a tubelike sheath with the reflected bulbar fascia.
• This sheath integrates into the muscle belly posteriorly and blends into Tenon's capsule anteriorly.

Conclusions:

• All rectus EOM fibers contribute to eye rotation.
• The CL is the structure observed in MRI scans, not the orbital layer insertion proposed by the active pulley hypothesis (APH).
• The APH requires re-evaluation, with alternative theories incorporating established neurophysiological and anatomical principles proposed.