The white part of the eye, known as the sclera, is a tough, protective outer layer composed primarily of dense collagen fibers. This layer maintains the eyeball’s shape and shields its delicate internal structures. When the sclera is not pure white, it can be concerning, as discoloration may represent a wide range of underlying issues. Changes in the sclera’s color are common and can signal anything from minor irritation to a serious systemic health condition requiring medical attention.
Systemic Causes: Why Eyes Turn Yellow
A generalized yellowing of the sclera is a sign of jaundice, which results from an excessive buildup of the yellow pigment bilirubin in the bloodstream. Bilirubin is a natural byproduct of the body’s process of breaking down old red blood cells. Normally, the liver filters bilirubin from the blood and processes it into bile, which is then excreted.
When the liver is unable to filter bilirubin effectively or its excretion pathway is blocked, the pigment accumulates in the body’s tissues, including the sclera. Underlying issues are often related to the liver, gallbladder, or bile ducts. For example, hepatitis causes inflammation of the liver tissue, impairing the liver cells’ ability to process bilirubin.
Blockages in the bile ducts, the small tubes that transport bile, also lead to bilirubin back-up and jaundice. Gallstones are a common cause of obstruction, as they can migrate to block the narrow ducts. Liver diseases like cirrhosis replace healthy liver tissue with scar tissue, severely limiting the organ’s function. If the entire sclera appears yellow, it indicates a systemic problem that must be evaluated by a healthcare professional.
Common Localized Changes: Redness and Irritation
The most frequent reason eyes appear not white is localized redness, which occurs when small blood vessels covering the sclera become dilated and more visible. This response is typically due to irritation, allergy, or infection affecting the conjunctiva, the thin membrane over the sclera. Conjunctivitis, commonly known as pink eye, is a cause of redness and inflammation resulting from viral, bacterial, or allergic triggers.
Another common change is a subconjunctival hemorrhage, which appears as a concentrated spot of bright red blood on the white of the eye. This is caused by a small blood vessel breaking beneath the conjunctiva, often due to a forceful cough, sneeze, or strain. Despite its appearance, this condition is harmless and resolves spontaneously as the body reabsorbs the blood over one to two weeks.
Persistent, generalized redness accompanied by a gritty or burning sensation may indicate dry eye syndrome. Dry eyes occur when the tear glands do not produce enough tears or when tears evaporate too quickly, leading to surface irritation. Environmental factors like prolonged screen time, wind, or dry air can exacerbate this condition, making blood vessels more prominent.
Benign Pigmentation and Scleral Growths
Not all discoloration is a sign of disease; some changes result from natural pigmentation or chronic exposure. Brown or gray patches on the sclera are often due to an excess of the dark pigment melanin, a condition called physiologic melanosis. These spots are essentially eye freckles, are more frequently observed in individuals with darker skin tones, and are generally present from birth or early childhood.
Long-term exposure to ultraviolet (UV) light and environmental irritants can lead to specific growths on the sclera. A pinguecula is a yellowish, slightly raised bump that forms on the conjunctiva, usually closer to the nose. If a pinguecula progresses, it can develop into a pterygium, a fleshy, wedge-shaped growth that may eventually extend over the cornea.
While both pinguecula and pterygium are non-cancerous, pterygium can cause vision problems if it grows over the central visual axis. Congenital pigment conditions, such as Nevus of Ota, can cause the sclera to display a gray or bluish discoloration. These pigmentations involve the deeper layers of the eye tissue and, while benign, require monitoring by an eye care specialist due to a small risk of melanoma.
Warning Signs: When to Seek Immediate Care
While many forms of eye discoloration are benign, certain accompanying symptoms necessitate immediate medical evaluation to protect vision. Any sudden and significant change in vision, such as blurriness, distortion, or the appearance of a dark curtain, is an emergency. These visual changes can signal serious issues like retinal detachment or an acute spike in eye pressure.
Severe eye pain, especially when combined with redness, light sensitivity, or blurred vision, suggests a serious inflammatory or infectious process, such as uveitis or acute glaucoma. If eye yellowing is accompanied by systemic symptoms, it could indicate a serious liver or biliary condition. Systemic symptoms include fever, unexplained fatigue, dark urine, or abdominal pain. A rapid increase in the number or size of floaters or new flashes of light also warrants urgent attention from an eye care professional.