The Function of the Sclera in a Human Eye

The sclera of the eye is better known as the white of the eye. The word "sclera" comes from the Greek word "skleros," which means hard. The plural of sclera is sclerae.

Diagram showing the structures of the human eye / Getty Images

The Sclera

The sclera is tough and fibrous, protecting the interior components of the eye from injury, and makes up the exterior coating of the eye. The sclera forms the entire visible white exterior of the eye, while the iris is the colored portion inside the anterior chamber of the eye.

Although we can only see the visible portion of the sclera, it actually surrounds the entire eye and provides structure for the internal contents of the eye, which are mostly made up of a thick liquid called the vitreous humor.

The sclera is composed of four layers. The inside layer is called the endothelium, followed by the stroma, the lamina fusca, and the episclera on the outside.

The Color of the Sclera

The sclera begins to turn yellow in individuals experiencing liver failure. This condition is called jaundice and indicates that the liver is no longer filtering the blood well.

In rare cases, the sclera can turn blue. This can be caused by long-term use of some medications, a rare condition called osteogenesis imperfecta (brittle bone disease), ingesting silver, and conditions that cause the sclera to be thin, which allows the blue color of veins to show through.

If you notice a color change in the sclera, you should seek advice from a healthcare professional.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. About Jaundice. Cleveland Clinic. July 2018.

  2. Siddiqui AA, Eghrari AO. Blue Sclera in Schmidt-Erfurth U, Kohnen T. (eds). Encyclopedia of Ophthalmology. Springer. 2014.

By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.