QS Study

Middle Vascular Coat of the Eyeball

The eye is the organ of sight. The vascular layer of the eye lies underneath the fibrous layer. It consists of the choroid, the ciliary body, and the iris.

The vascular layer or uveal tract makes up the vascular pigmented coat. It contains blood vessels that transmit blood throughout the eye.  The middle vascular coat or uveal tract of eyeball consists of the following three parts.

(A) Anterior: Iris. A free circular diaphragm with a central opening called a pupil. The diameter of the pupil is altered by smooth muscle fibers within the iris, which are innervated by the autonomic nervous system. It regulates the amount of light entering the eye by increasing or decreasing depending on the light intensity.

(B) Intermediate: Ciliary body. The ciliary muscle consists of a collection of smooth muscles fibers. The ciliary body controls the shape of the lens, and also contributes to the formation of aqueous humor.

(C) Posterior: Choroid. It provides nourishment to the outer layers of the retina.

Middle Vascular Coat of the Eyeball 1

Fig: Parts of Middle Vascular Coat of the Eyeball


  • Its major functions are oxygen supply and nutrition for the eye.
  • The iris with the pupil controls the amount of light entering the eye.
  • The ciliary body secrets aqueous humor and contains smooth muscles, responsible for changing the shape of the lens during accommodation.
  • The choroid, a vascular layer provides blood supply to the retinal pigment epithelium and the outer half of the sensory retina.
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