The appearance of a grey tint or spot in the white of the eye, known as the sclera, often causes concern for those who notice it. The sclera is the tough, opaque outer layer that covers most of the eyeball, providing protection and maintaining the eye’s spherical shape. While a perfectly white sclera is generally associated with health, temporary or permanent changes in color are common and can result from benign conditions or signal an underlying health issue. The causes of grey discoloration generally fall into two major categories: structural thinning that allows underlying tissue to show through, and the accumulation of foreign pigments or deposits within the tissue itself.
Why the Sclera Appears White
The sclera maintains its white color due to its unique structural composition. This protective layer is made up predominantly of collagen fibers, which are strong proteins also found in skin and bone. These collagen fibers are arranged in an irregular, crisscrossing pattern, which causes light to scatter randomly instead of passing straight through. This scattering effect, called opacity, is what makes the tissue appear white. The sclera’s primary functions are to provide a sturdy attachment point for the eye muscles and to act as a resilient barrier against injury. The white appearance is a consequence of this dense fiber arrangement, which effectively blocks the view of the darker structures inside the eye.
Grey Discoloration Due to Scleral Thinning
When the sclera’s integrity is compromised, it can become thinner or more translucent, allowing the dark underlying layers to become visible. This phenomenon often presents as a blue-grey discoloration, as the pigmented choroid—the vascular layer beneath the sclera and retina—shows through the weakened connective tissue. This structural change is referred to as “blue sclera” and is not caused by an added color, but rather by increased visibility of the eye’s natural internal pigment.
Scleral thinning is frequently associated with conditions that involve defects in collagen production. Osteogenesis Imperfecta (OI), sometimes called brittle bone disease, is a classic example where a genetic mutation affects the formation of Type I collagen, a major component of the sclera. In individuals with OI, the collagen fibers in the sclera are abnormally formed or reduced, leading to tissue that is more transparent than normal. Ehlers-Danlos Syndrome, a group of inherited disorders affecting connective tissues, can also result in a thinner, more fragile sclera due to structural collagen issues.
Less commonly, thinning may be acquired rather than congenital. Severe iron deficiency or long-standing anemia can impair the body’s ability to synthesize healthy collagen, which may lead to a reduced scleral thickness. Chronic inflammation, such as from certain types of uveitis, can also cause localized or diffuse weakening of the tissue over time. In infants, a mildly blue sclera can be a normal finding because their scleral tissue is naturally thinner and matures, becoming opaque, during the first year of life.
Grey Discoloration Due to Pigmentation and Deposits
The second major cause of grey sclera involves the localized accumulation of foreign or excess material within the tissue. Unlike the thinning mechanism, this discoloration is due to the presence of actual pigment or deposits. Ocular melanosis or a scleral nevus represents a common form, appearing as a slate-grey or bluish patch on the white of the eye. These are essentially freckles on the eye, caused by a higher concentration of melanin-producing cells within the sclera or episclera.
Scleral nevi are typically benign, congenital, and do not affect vision, but they require monitoring because they arise from the same cells that can potentially lead to melanoma. Another common cause is the long-term use of certain medications, particularly the antibiotic minocycline, often prescribed for acne or rosacea. Minocycline can cause a diffuse, often permanent, blue-grey or slate-grey discoloration of the sclera, as the drug’s metabolites deposit in the connective tissue.
This pigmentation is usually bilateral and not associated with vision loss, but it can also affect the skin, teeth, and nails. In rare cases, systemic metabolic or environmental factors lead to deposit accumulation. Ochronosis, a feature of the metabolic disorder Alkaptonuria, causes a dark, grey-brown pigment to build up in connective tissues, including the sclera. Argyrosis is a rare condition resulting from prolonged ingestion or exposure to silver compounds, causing silver particles to accumulate and manifest as a permanent, diffuse blue-grey discoloration.
When Grey Sclera Signals a Health Concern
While many causes of grey sclera are benign, such as a stable nevus or drug-induced pigmentation, any new or progressive change in eye color warrants professional evaluation. The most concerning signs are those that suggest an active or systemic disease process. If the grey discoloration is accompanied by sudden changes in vision, persistent eye pain, or significant redness and inflammation, consultation with an ophthalmologist is necessary.
Further medical attention is indicated if the discoloration is paired with other systemic symptoms, such as joint pain, easy bruising, hearing loss, or unexplained bone fractures. These symptoms may point toward a connective tissue disorder like Osteogenesis Imperfecta. When the grey color is new and localized, a comprehensive eye exam can differentiate a harmless pigment deposit from a potentially malignant lesion. For new or changing discoloration, a thorough evaluation is necessary to determine the underlying cause and ensure no sight- or life-threatening condition is present.