Foundation Volume 1, Chapter 22. Choroid and Suprachoroid

30 Апр 2014 | Author: | No comments yet »
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The uveal tract is a thin, brown, continuous layer composed primarily of blood vessels, melanocytes, and connective tissue. From anterior to posterior, the uveal tract has three distinct subdivisions: the iris, the ciliary body, and the choroid (Fig. 1 ). The iris and ciliary body are referred to as the anterior uvea. The posterior uvea is synonymous with the choroid.

Fig. 1. Uveal sphere with iris ( arrow ), ciliary body ( bracketed ), and choroid on right. Pupil on left and opening for optic nerve on right. (Courtesy of Stephen Gordon)

The uvea has a spherical shape containing two round openings. The anterior opening, the pupil, is bordered by the iris. The pupil diameter varies from 1 to 8 mm. The iris leaflet is bathed in aqueous humor and separates the anterior compartment into anterior and posterior chambers. The size and character of melanocyte pigment granules determines the iris color. The ciliary body lies between the iris and the choroid, functions during accommodation, and produces the aqueous humor. The iris joins the ciliary body near the recess of the anterior chamber angle. The anterior portion of the ciliary body is the pars plicata. The posterior portion of the ciliary body, the pars plana, merges with the choroid at the ora serrata. The choroid extends posteriorly from the ciliary body without interruption to the posterior opening of the uveal tract, the canal for the optic nerve. The optic canal is surrounded by the choroid and subjacent sclera.

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The uvea is firmly attached to the sclera at three sites: (1) anteriorly at the scleral spur; (2) at the exit of the vortex veins; and (3) posteriorly at the optic nerve. Potential spaces are present between the ciliary body and the sclera and between the choroid and the sclera. These contiguous potential spaces are called the supraciliary and suprachoroidal spaces, respectively. Internally, the entire uvea is lined by two continuous layers derived from the neuroectoderm. These layers serve distinct specialized functions in the three subdivisions of the uvea. The layers are described in segments as the anterior and posterior pigmented epithelium of the iris; the inner nonpigmented and outer pigmented ciliary body epithelium; and the inner neurosensory retina and the subjacent retinal pigment epithelium (RPE) (Fig. 2 ). The outer epithelial layer is separated from the underlying uvea by a continuous basement membrane. The remainder of this chapter will deal with the posterior uvea, the choroid.

Fig. 2. Inner layer ( arrow ) of the optic cup gives rise to the posterior iris pigmented epithelium, ciliary body nonpigmented epithelium, and the neurosensory retina. Outer layer ( arrowhead ) of the optic cup gives rise to the anterior iris pigmented epithelium, ciliary body pigmented epithelium, and the retinal pigment epithelium.

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