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Topic

design image
Cornea

The cornea is the transparent, avascular, dome-shaped anterior part of the eye that covers the iris, pupil, and anterior chamber. Acting as the primary refractive surface of the eye, the cornea contributes significantly to focusing incoming light onto the retina. Its structural clarity and curvature are essential for normal vision. Composed of five distinct layers—epithelium, Bowman’s layer, stroma, Descemet’s membrane, and endothelium—the cornea is continuous with the sclera at the limbus and is bathed anteriorly by the tear film and posteriorly by the aqueous humor.

Synonyms

  • Anterior transparent layer of the eye

  • Transparent eye covering

  • Ocular window

  • Corneal membrane

Function

  • Acts as the primary refractive medium of the eye, responsible for approximately two-thirds of the eye's total optical power

  • Protects the inner ocular contents from external injury, dust, and microorganisms

  • Filters ultraviolet (UV) light, providing some degree of protection to intraocular structures

  • Contributes to the structural integrity and shape of the globe

  • Maintains a moist environment via the tear film, essential for its transparency and function

MRI Appearance

  • T1-weighted (T1W) MRI:

    • The cornea appears hypointense (dark) relative to the surrounding orbital fat and vitreous.

    • Margins may be difficult to distinguish due to thinness and lack of contrast.

  • T2-weighted (T2W) MRI:

    • The cornea appears hypointense (dark) or isointense relative to the vitreous, as it is a highly organized, relatively dehydrated collagenous structure.

    • May be more easily differentiated from the hyperintense (bright) aqueous and vitreous humor.

  • STIR (Short Tau Inversion Recovery):

    • The cornea remains hypointense (dark) on STIR images.

    • The technique is useful in suppressing orbital fat and can improve delineation of the cornea against the suppressed fat signal, but the cornea itself does not show significant signal change.

CT Appearance

  • On CT (Computed Tomography):

    • The cornea is seen as a thin, hyperdense (bright) curvilinear structure at the anterior aspect of the globe.

    • Due to its small thickness and high density compared to the aqueous and vitreous, it is best appreciated on high-resolution axial and coronal reconstructions.

MRI images

Cornea mri image