Sclera

The sclera is 5% of the dense fibrous membrane of the eye and performs a protective and skeletal function, ie, it determines and ensures the shape of the eye. It is opaque, has a shiny white, tendon-like appearance.

The sclera consists of a dense collagenous tissue and elastic fibers, especially a lot of them in places where the muscles of the eye attach. Cellular elements of the sclera are poor, however, pigment cells are found in it, which are grouped mainly around the vessels and nerves passing through the sclera and sometimes are noticeable on the outer surface in the form of dark spots. The sclera is devoid of its own epithelial and endothelial integument.

Outside, the surface layers of the sclera are loose, they form a thin layer of the episclera, which merges with an even friable subconjunctival tissue of the eyeball. From the front, the sclera passes into the cornea, from behind its surface layers merge with the hard shell of the optic nerve.

The thickness of the sclera in different places varies between 0.4 and 1.2 mm. Slight thickness of the sclera in the region of the equator of the eye (up to 0.4 mm) and ahead of the attachment of the eye rectus muscles is insignificant. In the place of attachment of the eye muscles and especially in the circumference of the optic nerve, where its hard shell is woven into the sclera, the thickness of the sclera reaches 1.2 mm.

Sclera is poor in blood vessels and nerves. She receives blood from the anterior and posterior ciliary vessels, which form the episcleral network, which gives twigs to the sclera; sensitive nerves go in the sclera from long and short ciliary nerves. Through the sclera (near the optic nerve, in the equator, near the cornea), there are numerous arteries, veins and nerves for feeding and innervation of the cornea and the vascular tract of the eye. In the sclera there is less water than in the cornea, 10% protein and mucopolysaccharides.

The stroma of the sclera consists of collagen beams of various sizes and shapes that are not oriented as ordered as in the cornea.

The inner layer of the sclera (lamina fusca) passes into the suprachoroidal and supraciliary layers of the uveal tract.

The front of the epicler consists of a dense vascular connective tissue that lies between the superficial scleral stroma and the tenon capsule.

The front surface of the sclera is covered by three vascular layers.

1. Vessels of the conjunctiva are the most superficial layer; arteries are convoluted, veins are straight.
2. The vessels in the Tenon capsule have a straight path with a radial configuration. In episcleritis, the greatest stagnation of blood occurs in this vascular plexus. When palpated, it shifts over the surface of the sclera. The tenon capsule and episcler are infiltrated by inflammatory cells, and the sclera itself does not swell directly. The instillation of phenylephrine causes blanching of the conjunctiva and partly of the tenon capsule, allowing us to consider the subject of the sclera.
3. The deep vascular plexus is located in the surface layers of the sclera, and the maximum stasis associated with sclerites is associated with it. At the same time, some injection of surface vessels is inevitable, but it is insignificant. The instillation of phenylephrine does not affect the dilated vessels of this plexus. To locate the maximum injection level, a daylight inspection is necessary. The stroma of the sclera is mostly avascular.

[1], [2], [3], [4], [5], [6], [7], [8], [9]