The white part of the eye is called the sclera. It’s a tough, protective outer shell made of collagen fibers that wraps around nearly the entire eyeball, extending from the clear window at the front of your eye (the cornea) all the way to the optic nerve at the back. Despite being only about a millimeter thick, roughly the width of a credit card, the sclera is remarkably strong and gives the eye both its shape and its characteristic white color.
Why the Sclera Looks White
The sclera gets its white appearance from the way its collagen fibers are arranged. These fibers crisscross in a random, overlapping pattern that blocks most light from passing through. This is the opposite of the cornea, where collagen fibers are lined up in perfectly regular rows to let light through clearly. The random stacking in the sclera creates an opaque, white surface instead.
What the Sclera Actually Does
The sclera is the structural wall of your eyeball. It holds everything in place, maintains the eye’s round shape, and shields the delicate internal structures from physical damage. Six small muscles attach directly to the sclera’s surface, and these are the muscles that let you look up, down, and side to side without moving your head.
The sclera isn’t the same thickness everywhere. It’s thinnest near the middle of the eye (around 0.4 mm) and thickest at the back near the optic nerve (closer to 0.9 mm), where it needs to anchor the nerve connection to the brain.
The Conjunctiva: The Layer on Top
What you actually see when you look at someone’s “white of the eye” isn’t the sclera directly. It’s covered by a thin, transparent membrane called the conjunctiva, which contains tiny blood vessels. Those fine red lines you sometimes notice in your eyes are blood vessels in the conjunctiva, not in the sclera itself. When your eyes look bloodshot, those conjunctival vessels have dilated.
Where the Sclera Meets the Cornea
The border where the white sclera transitions into the clear cornea is called the limbus. You can see it as the subtle ring where the white part meets the colored iris. This narrow strip of tissue is more important than it looks: it houses stem cells that continuously regenerate the cornea’s surface, and it contains drainage channels that regulate fluid pressure inside the eye. The limbus also has a ring of circular fibers that help maintain the cornea’s curved shape, which is essential for focusing light properly.
What Color Changes in the Sclera Can Mean
A healthy sclera is white, so noticeable color changes can signal something worth paying attention to.
Yellow Sclera
Yellowing of the whites of the eyes, called scleral icterus, is one of the earliest visible signs of elevated bilirubin, a waste product normally processed by the liver. Bilirubin accumulates so easily in the tissue over the sclera that even slight increases can produce a yellow tint. Common causes include liver conditions (like cirrhosis or hepatitis), gallstones, certain genetic conditions like Gilbert’s syndrome and sickle cell disease, and even some medications including certain antibiotics and steroids. In newborns under two weeks old, mild yellowing is common and usually resolves on its own.
Blue or Gray Sclera
Sometimes the sclera takes on a blue or grayish tint. This happens when the sclera’s collagen fibers thin out enough to let the darker tissue layer underneath (the uvea) show through. In young children, a blue sclera often points to an inherited connective tissue condition. In adults, iron deficiency is a more common explanation.
Red Patches
A bright red spot on the white of the eye is usually a subconjunctival hemorrhage, a small broken blood vessel under the conjunctiva. It looks alarming but is typically harmless and clears up on its own within a week or two.
Inflammation of the Sclera
Two inflammatory conditions affect this part of the eye, and they differ significantly in severity.
Episcleritis is inflammation of the thin tissue layer just on top of the sclera. It causes redness and mild discomfort but rarely leads to complications. Only about 13.5% of people with episcleritis develop any ocular complications, and none in one large study experienced vision loss. It typically responds well to simple anti-inflammatory drops.
Scleritis is inflammation of the sclera itself, and it’s a much more serious condition. Nearly 60% of people with scleritis develop eye complications, and about 16% experience some degree of vision loss. The pain tends to be deep and severe, often waking people at night. Most cases require oral medications to control, and the more aggressive forms need powerful immune-suppressing drugs. People who also have an underlying autoimmune or systemic disease are at higher risk for vision problems, with 27% in that group losing some visual acuity compared to just 3% of those without a systemic condition.