The sclera, commonly known as the white of the eye, is a dense layer composed primarily of collagen fibers. It maintains the spherical shape of the eyeball and shields delicate internal structures from injury. The characteristic white appearance results from the irregular arrangement of these collagen bundles, which scatters light rather than allowing it to pass through clearly. Changes in the color of the sclera can signal various conditions, ranging from minor irritation to systemic health concerns.
Understanding Yellow Discoloration
Yellowing of the sclera, or jaundice, occurs due to the excessive accumulation of bilirubin in the bloodstream. Bilirubin is a yellowish pigment, a natural byproduct of the breakdown of old red blood cells. Normally, the liver processes and excretes this bilirubin from the body as a component of bile.
When the eyes turn yellow, it indicates that this normal metabolic process has been disrupted, leading to a buildup of unconjugated bilirubin. Liver diseases, such as hepatitis, cirrhosis, and alcohol-related liver damage, can impair the liver’s ability to efficiently process bilirubin. This results in a form of jaundice where the liver cells themselves are compromised.
Another common reason for bilirubin accumulation is an obstruction of the bile ducts, the drainage pathways for bile. Blockages caused by gallstones, tumors, or inflammation prevent the bile, and therefore the bilirubin, from reaching the small intestine. This obstructive jaundice causes bilirubin to back up into the bloodstream. While newborns often experience temporary jaundice as their livers mature, the sudden onset of yellow eyes in an adult warrants immediate medical evaluation.
Causes of Red or Bloodshot Eyes
Redness in the sclera is caused by the dilation and congestion of the tiny, superficial blood vessels. This vascular response is often a sign of inflammation or irritation of the conjunctiva, the thin membrane covering the sclera. Conjunctivitis, or pink eye, is a common cause, where blood vessels swell due to a viral, bacterial, or allergic infection. Viral conjunctivitis typically presents with a watery discharge, while bacterial forms often produce a thicker, pus-like discharge.
Allergies trigger redness when the immune system releases histamine, causing blood vessels to expand and leak fluid, resulting in diffuse redness, itching, and tearing. Environmental factors like eye strain, insufficient sleep, dry air, or contact lens overuse can also lead to chronic irritation and mild, persistent bloodshot eyes.
A different type of redness is a subconjunctival hemorrhage, which appears as a single, bright-red patch on the sclera. This occurs when a small blood vessel breaks beneath the conjunctiva, often due to a sudden increase in pressure from coughing, sneezing, vomiting, or straining. Although alarming, it is usually painless, harmless, and resolves on its own as the blood is reabsorbed, similar to a bruise.
Pigmentation, Thinning, and Other Color Changes
The sclera can display colors other than yellow or red due to changes in its structure or the presence of pigment. A blue or grayish tint occurs when the sclera is thinner than normal, allowing the dark color of the underlying choroid layer to show through. This thinning is natural in infants whose sclera has not fully matured, but it can also signal certain connective tissue disorders. Genetic conditions such as Osteogenesis Imperfecta (brittle bone disease) affect collagen production, reducing the sclera’s normal thickness and opacity.
In adults, localized brown or gray spots may be visible, which are typically benign accumulations of melanin pigment, known as scleral melanosis. These spots are similar to freckles on the skin and are often present from birth or early childhood. Certain medications, such as long-term use of minocycline, can also cause a diffuse blue-gray discoloration as the drug deposits in the tissue. While most pigmentation changes are benign, any new or rapidly changing dark spot on the eye should be examined by an eye care specialist.
Seeking Professional Medical Guidance
Any sustained change in the color of the sclera should be monitored, as it can indicate a health issue. A healthcare provider should evaluate yellow discoloration immediately, particularly if accompanied by symptoms like abdominal pain, fever, or unexplained weight loss, signaling a serious liver or gallbladder condition. Persistent redness accompanied by eye pain, sudden changes in vision, extreme light sensitivity, or a thick discharge requires prompt medical attention. These symptoms can suggest an infection, inflammation, or an acute increase in eye pressure, which could threaten vision. If a subconjunctival hemorrhage does not begin to fade after a week or recurs frequently, it should be investigated to rule out underlying issues like high blood pressure or a bleeding disorder.