Sclerotic

The sclerotic is another word for the sclera, which is also known as the the sclerotic coat.

The sclerotic is the tough white sheath that eyeball.

In all cases these names are due to the the extreme density and hardness of the sclerotic (sclerotic layer). It is a firm fibrous membrane that maintains the shape of the eye as an approximately globe shape. It is much thicker towards the back / posterior aspect of the eye than towards the front / anterior of the eye.

The white sclerotic continues around the eye, most of which is not visible while the eyeball is located in its socket within the face / skull. The main area of the eye that is not covered by the area is the front part of the eye that is protected by the transparent cornea instead.

Colour of the sclerotic

Although the sclerotic is commonly described as the 'white of the eye', its colour tends to change somewhat with age. The sclerotic is thinner and more translucent in children, enabling the underlying tissue to show through enough to give the sclerotic a slightly 'bluish' hue. As people age, the sclerotic of their eyes tend to take on a slightly yellow hue. In some cases very small blue-grey flecks or spots can appear on the sclerotic, which is a condition called scleral melanocytosis.

Structure of the sclerotic

The sclerotic is composed of white fibrous tissue intermixed with fine elastic fibers and corpuscles of flattened connective-tissue. These fibers are grouped together in bundles.

The sclerotic is supplied by many nerves and vessels that pass through the posterior scleral foramen, the hole in the sclerotic formed by the optic nerve. Blood supply to the sclerotic coat is via small interlinking capillaries.

For further detail see Gray's Anatomy, which is informative yet inexpensive.