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Topic

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Floor of orbit

The floor of the orbit forms the inferior boundary of the orbital cavity and separates the orbital contents from the maxillary sinus below. It is a thin, delicate bony plate that supports the globe and extraocular muscles while transmitting neurovascular structures through specific grooves and canals.

Anatomically, the orbital floor slopes gently upward from posterior to anterior and plays a critical role in orbital support, ocular alignment, and facial skeletal integrity. Due to its thinness, it is an important structure in radiologic evaluation of orbital anatomy and trauma.

Synonyms

  • Inferior wall of the orbit

  • Orbital plate of the maxilla

Location and Structure

  • Forms the inferior wall of the orbit

  • Separates the orbit from the maxillary sinus

  • Slopes upward and medially toward the orbital apex

  • Thin and smooth, especially in the central portion

Bony Components

  • Maxilla (orbital surface): Major contributor to the orbital floor

  • Zygomatic bone: Contributes to the anterolateral portion

  • Palatine bone (orbital process): Small posterior contribution

Relations

  • Superiorly: Orbital contents (globe, inferior rectus, inferior oblique muscles, orbital fat)

  • Inferiorly: Maxillary sinus

  • Anteriorly: Infraorbital margin

  • Posteriorly: Inferior orbital fissure

  • Medially: Lacrimal bone and ethmoid bone

  • Laterally: Zygomatic bone

Key Anatomical Features

  • Infraorbital groove: Runs posteriorly on the floor

  • Infraorbital canal: Continuation of the groove, transmitting infraorbital nerve and vessels

  • Inferior orbital fissure: Separates the floor from the lateral wall of the orbit

Function

  • Provides structural support to the globe and orbital contents

  • Protects the maxillary sinus from orbital structures

  • Forms a conduit for infraorbital neurovascular structures

  • Maintains orbital volume and ocular alignment

MRI Appearance

T1-weighted images:

  • Cortical bone: Very low signal (black)

  • Bone marrow (thin): Minimal, may show faint intermediate signal

  • Orbital fat above the floor: Bright signal

  • Maxillary sinus air below: Very low signal

  • Infraorbital canal: Linear low-signal cortical margins with surrounding fat

T2-weighted images:

  • Cortical bone: Low signal

  • Orbital fat: Intermediate-to-bright

  • Extraocular muscles: Intermediate signal

  • Maxillary sinus air: Signal void

  • Infraorbital canal: Well-defined dark cortical outline

STIR:

  • Cortical bone: Dark

  • Normal marrow: Intermediate-to-dark

  • Orbital fat: Suppressed

  • Extraocular muscles: Intermediate signal

  • Clean delineation between orbit and sinus due to fat suppression

T1 Fat-Saturated Post-Contrast:

  • Bone cortex: No enhancement

  • Normal marrow: Mild homogeneous enhancement if present

  • Orbital soft tissues: Uniform enhancement of vessels and muscles

  • Infraorbital canal margins: Non-enhancing cortical boundaries clearly seen

CT Appearance

Non-Contrast CT:

  • Orbital floor: Thin, sharply defined high-density bony plate

  • Maxillary sinus: Air-filled low-density cavity below the floor

  • Infraorbital canal: Clearly visualized as a tubular bony canal

  • Zygomatic and maxillary contributions easily differentiated

  • Best modality for detailed bony anatomy and thickness assessment

Post-Contrast CT:

  • Bone: No intrinsic enhancement

  • Orbital soft tissues: Homogeneous enhancement of vessels and muscles

  • Clear visualization of infraorbital canal relative to enhancing soft tissues

X-Ray Appearance

  • Waters (occipitomental) view:

    • Orbital floor seen as a smooth, curved radiopaque line forming the inferior orbital margin

    • Maxillary sinus appears as a radiolucent cavity beneath the floor

  • Caldwell view:

    • Partial visualization of orbital margins and inferior orbital contours

  • Lateral view:

    • Overlapping orbital structures with limited floor detail

CT image

Floor of orbit CT anatomy labelled image-img-00000-00000