The sclera is the tough white sheath that forms the outer-layer of the eyeball. It is also referred to by other names, including the sclerotic and the sclerotic coat (both of which have the same meaning as the word sclera).
In all cases these names are due to the the extreme density and hardness of the sclera (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 sclera 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 sclera
Although the sclera is commonly described as the 'white of the eye', its colour tends to change somewhat with age. The sclera is thinner and more translucent in children, enabling the underlying tissue to show through enough to give the sclera a slightly 'bluish' hue. As people age, the sclera 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 sclera, which is a condition called scleral melanocytosis.
Structure of the sclera
The sclera 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 sclera is supplied by many nerves and vessels that pass through the posterior scleral foramen, the hole in the sclera formed by the optic nerve. Blood supply to the sclera is via small interlinking capillaries.
For further detail see Gray's Anatomy, which is informative yet inexpensive.
More about Ophthalmology:
This section includes short definitions and descriptions of the parts of the eye.
For other descriptions in this category, choose from the list to the left (but note that this is not a complete / exhaustive list).
Other related sections include:
- A labelled diagram of the eye
- A concise description of the human retina with brief descriptions of the parts of the retina
- Diseases and disorders of the human eye and the human visual system
- Clinical and surgical procedures re. eyes and human visual system
For further information see also our pages of books about ophthalmology.