The cornea is the clear, dome-shaped tissue at the front of the eye that covers the iris, pupil, and anterior chamber, and its transparency is essential for its primary function: focusing light. Corneal pigmentation is the deposition of colored material within the layers of this structure. This discoloration can range from a faint, asymptomatic line to a dense opacity that severely affects eyesight. The deposited material may originate from sources like iron, copper from systemic processes, or external substances such as medication or tattoo ink. Identifying the source and location of the pigment is crucial for distinguishing between a harmless sign of aging and a potentially serious underlying health condition.
Pigmentation Related to Normal Aging
Some forms of corneal pigmentation occur naturally over time and are generally not a cause for concern.
The Hudson-Stahli line is one of the most frequently observed types, appearing as a thin, horizontal, brownish-yellow line in the lower third of the cornea. This pigmentation is caused by the deposition of iron particles, specifically hemosiderin, within the corneal epithelium, likely due to the pooling and evaporation of the tear film. The line is common, increases with age, and typically does not cause symptoms or require treatment.
Another common age-related change is the Limbal Girdle of Vogt, characterized by a thin, whitish-yellow band near the edge of the cornea, separated from the limbus by a clear zone. This change relates to elastotic degeneration, similar to changes seen in sun-exposed skin. Like the Hudson-Stahli line, the Limbal Girdle of Vogt is a benign finding that poses no threat to visual acuity.
Axenfeld’s Loop is a benign pigmented area marking where a long posterior ciliary nerve loops forward before re-entering the sclera. Although found very close to the corneal edge, it is not strictly on the cornea. It appears as a small, grey or dark spot. This anatomical variant is normal and harmless, though it can sometimes be mistaken for a foreign body.
Pigmentation Signifying Systemic Disease
Corneal pigmentation can signal a serious metabolic or genetic disorder affecting other organ systems. The most clinically significant example is the Kayser-Fleischer (KF) ring. These rings are bilateral, golden-brown, or greenish-brown copper deposits located in the Descemet membrane, the innermost layer of the cornea.
The presence of KF rings strongly indicates Wilson’s Disease, a rare, inherited disorder where the body cannot properly excrete excess copper. This leads to toxic copper accumulation in the liver, brain, and eyes. The rings typically appear first at the top of the cornea, then the bottom, eventually forming a complete ring around the iris.
While the rings rarely impair vision, their discovery necessitates immediate systemic evaluation and treatment to prevent life-threatening liver failure or neurological damage. Diagnosis requires blood and urine tests to measure copper levels. Timely anti-copper therapy, using medications like zinc acetate or chelating agents, can halt disease progression and may cause the KF rings to fade or disappear. Similar corneal pigmentation has also been reported in patients with severe cholestatic liver diseases where bile flow is impaired.
Pigmentation from Local or External Causes
Corneal pigmentation can result from external factors, such as pharmaceutical drugs, or from localized events within the eye, like trauma.
Drug-Induced Pigmentation (Vortex Keratopathy)
Drug-induced pigmentation, known as vortex keratopathy or cornea verticillata, is a common side effect of certain systemic medications, most notably the antiarrhythmic drug Amiodarone. The pigment appears as fine, brownish-yellow, whorl-like deposits in the corneal epithelium, radiating outward from a central point. These deposits are found in nearly all patients taking Amiodarone long-term.
While they rarely cause significant vision loss, they can lead to visual disturbances such as seeing halos around lights or blurred vision. This pigmentation is generally reversible, with deposits slowly clearing months after the medication is discontinued. Other drugs, including certain antimalarials and phenothiazines, can also cause similar epithelial pigment deposition.
Corneal Blood Staining
A more serious localized cause is corneal blood staining, which follows a significant hyphema (blood collection in the anterior chamber), typically due to blunt eye trauma. When intraocular pressure is elevated, hemoglobin from the trapped red blood cells breaks down and impregnates the corneal stroma layers. This process leaves a dense, brown or dark yellow opacity due to hemosiderin deposition, which can severely compromise vision.
Clearing of this staining is a slow process that can take many months or years, starting from the periphery as the pigment is metabolized by corneal cells. The risk of this staining is higher with total hyphemas and when high pressure persists for several days.
Keratopigmentation (Corneal Tattooing)
Deliberate corneal pigmentation, known as keratopigmentation or corneal tattooing, involves injecting colored pigment into the corneal layers. This procedure is sometimes performed for reconstructive cosmetic purposes, such as masking a dense white scar or reducing glare from a damaged iris. The practice of corneal tattooing purely for aesthetic reasons to change eye color carries significant risks, including infection, inflammation, and potential vision loss. Injected pigments, especially those containing iron, may change color over time, often shifting to an undesirable golden-brown hue years after the initial procedure.
Identifying and Treating Corneal Pigmentation
Identifying corneal pigmentation relies heavily on a specialized eye examination using a slit lamp biomicroscope. This instrument allows the eye care professional to visualize the cornea under high magnification and determine the exact location, shape, color, and depth of the deposits. The appearance alone often suggests the cause; for example, a whorl-like pattern points toward drug toxicity, while a peripheral golden ring indicates copper deposition.
If a systemic cause like Wilson’s Disease is suspected, the eye examination is followed by blood work, urine tests, and sometimes genetic testing to confirm the diagnosis and assess organ involvement. For drug-induced pigmentation, management involves consulting the prescribing physician to determine if the medication can be safely reduced or replaced. Since most drug-related deposits and benign age-related lines do not affect vision, the primary intervention is careful monitoring.
Treatment is generally directed at the underlying cause rather than directly removing the pigment. A corneal transplant may be necessary in cases of severe corneal blood staining that fails to clear spontaneously and causes profound vision loss, or when a dense scar requires correction. For the vast majority of corneal pigmentations, the most appropriate course of action is observation and addressing the systemic issue to protect overall health and vision.