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Topic

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Eyeball

The eyeball (globe) is a spherical sensory organ housed within the orbit, responsible for vision. It consists of three layers—fibrous, vascular, and neural—and contains optical structures including the cornea, lens, aqueous humor, vitreous body, and the retina.

The globe measures approximately 24 mm in transverse diameter and is suspended within the orbit by extraocular muscles, fascial sheaths, and fat. It maintains constant intraocular pressure and precise optical alignment, allowing accurate light refraction and image formation on the retina.

Synonyms

  • Globe

  • Bulbus oculi

Location and Structure

  • Position: Occupies the anterior two-thirds of the orbit

  • Shape: Spherical anteriorly with slight posterior taper

  • Layers:

    • Fibrous layer: Sclera and cornea

    • Vascular (uveal) layer: Choroid, ciliary body, iris

    • Neural layer: Retina

  • Internal chambers:

    • Anterior chamber (aqueous humor)

    • Posterior chamber (aqueous humor)

    • Vitreous chamber (vitreous humor)

  • Optical structures: Cornea, lens, retina, optic nerve head

Relations

  • Anteriorly: Conjunctiva, eyelids, cornea

  • Posteriorly: Optic nerve, short ciliary nerves and vessels

  • Superiorly: Superior rectus and levator palpebrae superioris

  • Inferiorly: Inferior rectus, orbital floor

  • Medially: Medial rectus, ethmoid sinus

  • Laterally: Lateral rectus, lacrimal gland

Attachments

  • Six extraocular muscles insert into the sclera

  • Tenon’s capsule surrounds the globe

  • Optic nerve attaches posteriorly at the optic disc

  • Ciliary zonules suspend the lens

Function

  • Vision: Receives, refracts, and focuses light onto the photoreceptive retina

  • Accommodation: Lens changes curvature for near/far focus

  • Light regulation: Iris controls pupil size

  • Protection: Sclera and cornea shield internal components

  • Image transmission: Retina converts light signals to electrical impulses via optic nerve

MRI Appearance

T1-weighted images:

  • Vitreous: Very low signal (dark)

  • Lens: Low signal; defined biconvex structure

  • Cornea/Sclera: Low signal rim encasing the globe

  • Choroid/Retina: Thin intermediate-signal layer

  • Orbital fat: Bright, providing strong contrast against globe structures

T2-weighted images:

  • Vitreous: Very bright hyperintense fluid signal

  • Lens: Dark, non-signal-producing

  • Sclera: Dark rim; choroid mildly hyperintense

  • Aqueous humor: Bright, similar to CSF

  • Extraocular muscles: Intermediate-to-dark signal adjacent to globe

STIR:

  • Vitreous: Bright, though slightly suppressed compared to T2

  • Extraocular muscles: Intermediate signal

  • Orbital fat: Suppressed (dark), increasing contrast of globe boundaries

  • Sclera: Dark, clearly defined

3D T2 (SPACE / CISS / DRIVE):

  • Vitreous: Uniformly bright

  • Lens and sclera: sharply dark, well-demarcated

  • Retina/choroid complex: Visible as thin layered structures

  • Optic nerve sheath complex: Excellent delineation with high-resolution multiplanar reconstructions

T1 Fat-Saturated Post-Contrast

  • Globe interior (normal): No enhancement

  • Choroid: Mild uniform enhancement (vascular layer)

  • Optic nerve head: Subtle enhancement due to vascularity

  • Sclera and cornea: No enhancement

  • Enhances well the adjacent soft tissues, muscles, and orbital vessels

CT Appearance

Non-Contrast CT:

  • Globe: Homogeneous near-fluid attenuation

  • Lens: Hyperdense biconvex structure

  • Sclera: Thin hyperdense rim

  • Vitreous chamber: Low attenuation similar to water

  • Calcified structures: Scleral plaques may be seen in elderly

  • Excellent for detecting foreign bodies, fractures, and orbital emphysema

Post-Contrast CT:

  • Globe (normal): No intravitreal enhancement

  • Choroid and retinal circulation: Subtle thin enhancement around inner globe

  • Extraocular muscles and optic nerve sheath: Moderate enhancement

  • Helps delineate orbital soft tissues, lacrimal system, and vascular structures

MRI image

Eyeball MRI axial image-img-00000-00000

CT image

Eyeball CT image