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Choroid

The choroid is a vascular layer of the eye located between the retina and the sclera. Rich in blood vessels and connective tissue, it provides essential nutrients and oxygen to the outer layers of the retina. The choroid plays a crucial role in ocular health and visual function, and its evaluation is important in various ophthalmic and neurological conditions. On imaging, particularly MRI and CT, the choroid exhibits characteristic appearances that help distinguish it from surrounding ocular structures.

Synonyms

  • Uveal layer (when combined with ciliary body and iris)

  • Vascular tunic (of the eye)

  • Choroidea

Function

  • Provides oxygen and nourishment to the outer retina

  • Acts as a light-absorbing layer to prevent internal reflection within the eye

  • Contributes to temperature regulation and waste removal in retinal tissues

  • Part of the blood-ocular barrier

  • Supports the metabolic needs of photoreceptor cells

MRI Appearance

  • T1-Weighted (T1W):

    • The choroid appears as a thin, slightly hyperintense or isointense band compared to vitreous humor

    • Distinct from the hypointense sclera and hyperintense intraocular fat

  • T2-Weighted (T2W):

    • The choroid demonstrates moderate hypointensity compared to vitreous

    • May appear less well-defined due to partial volume averaging with retina and sclera

    • Hyperintense in pathologies with increased fluid content (e.g., choroidal effusion)

  • STIR (Short Tau Inversion Recovery):

    • Signal suppression of intraorbital fat enhances visualization

    • The choroid appears as a thin hypointense band

    • Useful in detecting abnormal thickening, edema, or choroidal tumors

CT Appearance

  • On non-contrast CT, the choroid is not well visualized due to its thinness and similarity in attenuation to adjacent ocular structures

  • With contrast-enhanced CT, the choroid may show mild enhancement due to its vascularity

MRI images

Choroid mri sagittal t2 image