The appearance of a grey or bluish tint in the whites of the eyes, known medically as the sclera, often raises questions about eye and general health. The sclera is the dense, opaque outer layer of the eyeball, primarily composed of collagen fibers. Its typically bright white color is a sign of its thickness. When the sclera changes to a subtle blue or grey, it signals an alteration in the underlying tissue or the presence of foreign pigment.
Is It Simply Natural Pigmentation?
A greyish tint in the sclera is not always an indication of a medical problem, as natural variations in pigmentation can account for the appearance. Individuals with darker skin tones may naturally exhibit a darker or speckled sclera due to benign melanin deposition. Melanin, the pigment responsible for skin and hair color, can create harmless, slate-grey or brownish patches on the white of the eye, a condition sometimes called scleral melanocytosis. These spots are usually stationary and do not affect vision. In older adults, localized greyish-yellow patches called senile scleral plaques can appear near the edges of the cornea, representing benign, age-related calcification of the scleral tissue.
The Mechanism of Scleral Thinning
The most frequent physical cause for a uniformly grey or blue sclera is a reduction in its normal thickness. The sclera is typically a robust, opaque layer of connective tissue, but when it becomes abnormally thin or translucent, it no longer effectively masks the dark layer beneath it. Directly underneath the sclera lies the choroid, a vascular layer rich in dark brown pigment and blood vessels. When the sclera thins, the dark color of the choroid shows through the translucent tissue. This thinning occurs naturally in infants because their sclera is not yet fully developed, with the blue tint typically resolving by six months of age. Acquired scleral thinning can occur later in life due to chronic conditions like iron deficiency anemia or long-term use of certain medications, such as corticosteroids, which affect collagen metabolism.
Systemic Connective Tissue Conditions
A persistent blue or grey sclera can indicate a systemic disorder affecting the body’s connective tissue, specifically its collagen structure. Osteogenesis Imperfecta (OI), often known as brittle bone disease, is caused by a genetic defect in the production of Type I collagen. Since Type I collagen is a major structural component of both bone and the sclera, a flaw in this protein results in fragile bones and a thinner, more transparent sclera. The blue tint in OI, particularly Type I, is a characteristic sign, frequently appearing alongside recurrent bone fractures, short stature, and hearing loss.
Ehlers-Danlos Syndrome (EDS) is another group of genetic disorders that impairs collagen synthesis and structure. The faulty collagen in EDS leads to hypermobile joints and unusually elastic, fragile skin, compromising the structural integrity of the sclera. The resultant thinning allows the underlying pigmented layers to become visible, manifesting as a blue or grey hue.
Drug and Metabolic Pigmentation
Discoloration of the sclera can sometimes be due to the deposition of foreign substances or metabolic waste products rather than thinning. A notable drug-induced cause is the long-term use of the antibiotic Minocycline, which can lead to blue-grey hyperpigmentation. The drug’s breakdown products bind to collagen in the sclera, resulting in a localized, slow-to-resolve discoloration. This pigmentation is often cosmetic and harmless to the eye’s function.
Rare metabolic disorders can also cause distinct pigmentation changes in the sclera. Ochronosis, an inherited condition linked to alkaptonuria, involves a lack of the enzyme homogentisate oxidase. This causes homogentisic acid to accumulate in connective tissues. The acid polymerizes into a dark pigment that deposits in the sclera, ears, and cartilage, leading to a dark grey or brownish-black discoloration.
When to Consult an Eye Doctor
While some scleral discoloration is benign, a professional evaluation is necessary to rule out underlying systemic issues. Consult an eye doctor if the grey or blue tint appears suddenly in adulthood or is noticeably worsening over time. Any change in the sclera’s color that is asymmetrical, appearing in only one eye or unevenly between them, warrants attention.
Consultation is important if the discoloration is accompanied by other physical symptoms. These signs include new or frequent bone fractures, unexplained joint pain or hypermobility, hearing loss, or changes in vision such as blurriness or pain. A comprehensive eye examination can determine the exact cause of the discoloration and establish whether medical management is required.