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As I mentioned, one of the fascinating parts about orbital

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imaging is the anatomy. In general,

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we think about the anatomy in separating orbital

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pathology into ocular pathology,

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followed by intraconal and extraconal pathology, and

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therefore we have to know the anatomy

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of these different spaces.

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So let's start with the anatomy of

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the globe or ocular anatomy.

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The globe has an anterior segment which includes the anterior

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portions of the eyeball in front of the iris,

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so that includes the anterior chamber

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and the posterior chamber.

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The posterior segment includes the vitreous and also includes

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the attachment of the optic nerve to the back of the globe and

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the associated ocular membranes, which include the sclera,

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the choroid, and the retina.

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In general, we evaluate the globe in two portions,

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the anterior segment and the posterior segment.

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The anterior segment includes the cornea,

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which is a reflection of the sclera going anteriorly over the eye.

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Behind the cornea, one finds the anterior chamber.

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The anterior chamber has aqueous fluid which should have both

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the density and the signal intensity of cerebrospinal fluid.

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Behind the anterior chamber one comes into

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the iris and the iris is part of the UVEA.

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The UVEA includes the ciliary body,

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which has muscular attachments to the lens to stretch it,

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and it also includes the choroid, which, as you can see,

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communicates with the ciliary body anteriorly.

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The posterior chamber is identified behind the iris

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and is a very small area of anatomy which we do

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not see typically on CT nor on MRI scanning.

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However, we do see this structure, which is the ora serrata.

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The ora serrata is the junction between the retina

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and the choroid process and the ciliary body.

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So this is the communication between

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the retina and the ciliary body.

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The retina does not extend as far anteriorly as

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the choroid does. It stops at the ora serrata.

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We usually say that the ora serrata is at

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about 10 o'clock and 2 o'clock on the globe.

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The posterior segment includes the vitreous humor,

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which is approximately two-thirds of the volume of the globe.