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Topic

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Sclera

The sclera is the dense, fibrous, opaque outer layer of the eyeball, commonly referred to as the “white of the eye.” It provides structural support and protection to the eye, maintaining its shape and serving as an attachment site for extraocular muscles. The sclera is continuous with the cornea anteriorly and merges with the optic nerve sheath posteriorly. Its toughness and resilience help protect the delicate intraocular components from injury and deformation.

Synonyms

  • White of the eye

  • Tunica fibrosa oculi (outer fibrous tunic of the eye)

  • Ocular sclera

  • Sclerotic coat

Function

  • Provides structural integrity and maintains the shape of the globe

  • Acts as a protective barrier against physical and infectious insults

  • Serves as an attachment point for the extraocular muscles, facilitating eye movement

  • Supports intraocular pressure and prevents globe collapse

  • Separates intraocular components from the orbital cavity

MRI Appearance

  • T1-Weighted Images (T1):

    • Sclera appears hypointense (dark) due to its dense collagenous composition and low water content.

  • T2-Weighted Images (T2):

    • Sclera remains markedly hypointense (very dark) compared to surrounding orbital fat and intraocular structures, as it is relatively avascular and has low hydrogen proton density.

  • STIR (Short Tau Inversion Recovery):

    • Sclera appears hypointense (dark) as STIR sequences suppress fat and highlight tissues with higher water content, while the sclera’s low water composition causes it to stay dark.

CT Appearance

  • On CT scans, the sclera is seen as a thin, hyperdense (bright/white) outer rim of the globe, easily distinguished from the relatively hypodense intraocular contents and orbital fat.

MRI images

sclera mri t2 sagittal image