sclera

n. white fibrous membrane which covers the eye (Anatomy)

The sclera is the opaque (usually white), fibrous, protective layer of the eye containing collagen and elastic fibers. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the old, however, fatty deposits on the sclera can make it appear slightly yellow.The sclera forms the posterior five sixths of the connective tissue coat of the globe. The sclera maintains the shape of the globe, offering resistance to internal and external forces, and provides an attachment for the extraocular muscle insertions. The thickness of the sclera varies from 1mm at the posterior pole to 0.3 mm just behind the rectus muscle insertions.
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Sclera /scle·ra/ pl. scle´rae [L.] the tough white outer coat of the eyeball, covering approximately the posterior five-sixths of its surface, [more]Sclera - Community and Resources

Noun
1. whitish fibrous membrane (albuginea) that with the cornea forms the outer covering of the eyeball
(synonym) sclerotic coat
(hypernym) albuginea
(part-holonym) eye, oculus, optic

the white, dense, fibrous outer coating of the eyeball.
(See Anatomy of the Eye" on the MD Support web site.)