634 THE EYE 



THE SCLERA 



The sclera (sclerotic coat) is a firm opaque connective tissue mem- 

 brane which forms the outermost layer of the posterior segment of the 

 eyeball. It consists of two layers, the thick, firm, substantia propria, 

 and the very thin, innermost, delicate, lamina fusca. 



By reflected light the sclera of the adult is of a lustrous white color. 

 In the child it has a faint bluish tint, due to the presence of pigment in 

 the deeper layers of the child's eye which shows indistinctly through 

 the relatively clear superficial tissues. The anterior portion of the 

 sclera is covered by the bulbar conjunctiva and is familiarly known as 

 the 'white of the eye.' A yellowish patch in the vicinity of the corneal 

 margin, known as the pinguecula, may be present, especially in old 

 age. It is believed to be due to irritation from dust, leading to colloid 

 infiltration of the conjunctival stroma. 



That portion of the sclera which is posterior to the ocular equator 

 is covered by the visceral layer of the capsule of Tenon except at the 

 insertions of the straight and oblique muscles. The tendons of these 

 muscles pierce the capsule and are obliquely inserted into the surface of 

 the sclera in a line nearly corresponding to the equator of the eye. The 

 tendon bundles of the muscles are directly continuous with the fibrous 

 bundles which compose the sclera. 



The Substantia Propria. The collagenous fibrous tissue of the 

 sclera is disposed in bundles which are arranged along meridional and 

 equatorial lines; they interlace with one another to form a dense net- 

 work. A few elastic fibers are interspersed among the bundles of this 

 network. Stellate connective tissue cells, the scleral corpuscles, lie in the 

 interfascicular clefts. Occasional pigmented cells are also sometimes 

 present. 



The Lamina Fusca. The inner surface of the sclera presents a fine 

 gauzy membrane which can be readily detached by teasing. This is the 

 lamina fusca sclerae. It consists of delicate interlacing fibrous bundles 

 and numerous pigmented connective tissue cells. The lamina fusca near 

 the posterior pole is firmly adherent to the scleral substance. 



At the posterior pole of the eye the sclera is pierced by the optic 

 nerve, whose numerous bundles penetrate the coats of the eyeball and 

 give to this portion of the sclera a cribrose appearance. This area of the 

 sclerotic coat is known as the lamina cribrosa sclerce. It is a circular 

 zone whose border is outlined by the entrance of the posterior ciliary 

 arteries and the ciliary nerves. This is the thickest portion of the sclera, 



