# What is the tunics of the eye?

Gray’s Anatomy (1918) describes the tunics of the eye as follows: From without inward the three tunics are: (1) A fibrous tunic, consisting of the sclera behind and the cornea in front; (2) a vascular pigmented tunic, comprising, from behind forward, the choroid, ciliary body, and iris; and (3) a nervous tunic, the retina.

## What it means

- From without inward the three tunics are: (1) A fibrous tunic, consisting of the sclera behind and the cornea in front; (2) a vascular pigmented tunic, comprising, from behind forward, the choroid, ciliary body, and iris; and (3) a nervous tunic, the retina. The Fibrous Tunic ( tunica fibrosa oculi ).
- —The sclera and cornea form the fibrous tunic of the bulb of the eye; the sclera is opaque, and constitutes the posterior five-sixths of the tunic; the cornea is transparent, and forms the anterior sixth. The Sclera. —The sclera has received its name from its extreme density and hardness; it is a firm, unyielding membrane, serving to maintain the form of the bulb. It is much thicker behind than in front; the thickness of its posterior part is 1 mm.
- Its external surface is of white color, and is in contact with the inner surface of the fascia of the bulb; it is quite smooth, except at the points where the Recti and Obliqui are inserted into it; its anterior part is covered by the conjunctival membrane.
- Its inner surface is brown in color and marked by grooves, in which the ciliary nerves and vessels are lodged; it is separated from the outer surface of the choroid by an extensive lymph space ( spatium perichorioideale ) which is traversed by an exceedingly fine cellular tissue, the lamina suprachorioidea. Behind it is pierced by the optic nerve, and is continuous through the fibrous sheath of this nerve with the dura mater.
- Where the optic nerve passes through the sclera, the latter forms a thin cribriform lamina, the lamina cribrosa scleræ; the minute orifices in this lamina serve for the transmission of the nervous filaments, and the fibrous septa dividing them from one another are continuous with the membranous processes which separate the bundles of nerve fibers. One of these openings, larger than the rest, occupies the center of the lamina; it transmits the central artery and vein of the retina.
- Around the entrance of the optic nerve are numerous small apertures for the transmission of the ciliary vessels and nerves, and about midway between this entrance and the sclerocorneal junction are four or five large apertures for the transmission of veins ( venæ vorticosæ ).

## Sources

- [Gray's Anatomy of the Human Body (1918)](https://www.bartleby.com/lit-hub/anatomy-of-the-human-body/1c-1-the-tunics-of-the-eye/)

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