Quick Answer
There are a few possible causes for eyes changing color randomly:
– Heterochromia iridum: A rare condition where the iris in one eye is a different color than the other. This is present from birth.
– Eye freckles: Iris freckles or nevi can cause random darker spots or flecks to appear in the iris. These are benign.
– Fuchs heterochromic iridocyclitis: An inflammatory eye condition that can cause one eye to change to a lighter blue, gray or brown color over time.
– Medications: Certain medications like anti-glaucoma eye drops or chloroquine can deposit pigment in the iris and cause color changes. These are usually temporary.
– Injuries: Trauma to the eye can disrupt the iris and cause permanent color changes in part of the iris.
– Eye tumors: Cancerous and benign tumors in the eye, like iris melanoma or nevi, may alter iris pigmentation in areas.
– Age: The iris may gradually lighten or gain more brown spots as a normal part of aging.
What is the Iris?
The iris is the colored part of the eye that controls the size of the pupil and amount of light that enters the eye. It sits behind the clear cornea and in front of the lens.
The color of the iris comes from the amount and distribution of melanin pigment within the anterior border layer of the iris tissue. More melanin concentrated in one area makes the iris look darker brown. Less melanin results in blue or light colored eyes.
Iris Anatomy
The iris has two layers of tissue:
– Anterior border layer: Composed of collagen and melanocytes which produce melanin pigment granules. The amount and pattern of melanin in this layer gives the eye its color.
– Stroma: Made up of pigment epithelial cells, blood vessels, and the sphincter and dilator muscles that control pupil size. The stroma appears lighter.
The iris has a pupillary zone around the pupil and a ciliary zone between the pupil and white sclera. Crypts, furrows, a wreath pattern, and collarette with flower petal shapes are visible iris surface landmarks.
Causes of Iris Heterochromia
There are several possible reasons why one or both eyes may change color or have different coloration:
Heterochromia Iridum
Heterochromia iridum is a rare condition where the iris in one eye has a different color than the other. This can be:
– Complete: One iris is a distinctly different color, like one brown eye and one blue eye.
– Sectoral: Part of one iris is a different color from the rest.
– Central: A ring around the pupil is a different color.
This type of heterochromia is present at birth or develops in early childhood as the melanin content in each iris is determined. Heterochromia iridum affects about 200,000 people in the United States.
Causes include:
– Genetics: Heterochromia runs in families and may be passed down genetically. The genetics are not fully understood.
– Congenital Horner’s syndrome: A birth condition affecting nerves which control pupil dilation that can cause one iris to have less melanin.
– Waardenburg syndrome: A genetic disorder that can result in differently colored eyes.
– Injury or disease: Any trauma, inflammation, or tumor that affects melanocyte cells in the infant iris early in life can inhibit normal pigmentation.
Eye Freckles
Eye freckles are small areas of increased melanin production in the iris that look like dark spots or flecks in the colored part of the eye. They may appear darker brown, black or yellow. These freckles are also called iris nevi or iris melanosis.
Eye freckles are benign and don’t require treatment. They are similar to freckles on the skin that appear with sun exposure. Causes include:
– Sun damage
– Inflammation
– Normal aging process
Eye freckles tend to develop later in childhood or adulthood. They may run in families. Around 10% of adults have them. Over time, some flecks may increase in size or change color slightly.
Fuchs Heterochromic Iridocyclitis
Fuchs heterochromic iridocyclitis is a chronic inflammatory eye disease that usually only affects one eye. It can cause the iris to gradually change color over months or years due to loss of pigmentation.
In the early stages, the affected eye may look lighter. Eventually it may appear a different color like gray, brown or blue compared to the other eye. Other symptoms include floaters, glaucoma, cataracts and blurred vision.
The exact cause is unknown but risk factors include rubella or toxoplasmosis infection, trauma to the eye, or genetics. It’s believed the inflammation destroys the pigment producing cells in the anterior border layer of the iris. Treatment involves controlling inflammation with eye drops or medication.
Medication Side Effects
Certain prescription eye drops or oral medications can cause an accumulation of pigment granules in the iris stroma that alters the eye color. These medication side effects are usually temporary and the iris color reverts after stopping treatment.
Examples include:
– Anti-glaucoma prostaglandin analog eye drops like latanoprost or bimatoprost. Increased brown pigmentation occurs in 15-50% of those using these types of drops. The more drop used, the longer the use, the darker the change.
– Chloroquine or hydroxychloroquine pills used to treat malaria, rheumatoid arthritis or lupus. These medications can bind to melanin and cause a permanent ring of brown pigment to develop around the pupil. Regular eye exams are needed to monitor for vision changes.
Eye Injuries
Trauma to the eye from an injury that damages the iris can cause permanent heterochromia. Loss of pigmentation occurs in the injured area of the iris due to disruption of the pigment producing cells. Parts of the iris may look lighter or even white where the trauma occurred.
– Chemical burns
– Blunt force trauma
– Penetrating injuries from a foreign object
– Surgical trauma during eye surgery
The amount of color change depends on the severity and location of the injury. Iris repair and regeneration of pigment after trauma is limited.
Eye Tumors
Rarely, cancerous or benign tumors arising in the eye can alter melanin content and cause iris heterochromia:
– Uveal melanoma: Melanoma of the iris pigment cells is rare but can appear as a heterchromic brown or yellow nodule that changes the color in part of the iris.
– Iris nevus: A benign freckle-like growth that develops on the colored part of the eye, often in childhood. They appear as flat, well-defined dark spots on the iris surface due to increased melanocyte cells. Larger nevi may have cysts and fluid-filled gaps that make the iris appear darker brown or multicolored in that area.
– Iris cysts: Can displace normal iris tissue and alter local pigmentation.
– Metastatic cancer: If melanoma, breast cancer or other cancers spread to the eye, they can disrupt the iris.
Aging
As people age, the iris may gradually change color or gain pigmentation spots due to natural changes in melanin concentration in the border layer cells.
– The overall iris may lighten slightly over decades as melanin degrades. Blue eyes in particular can develop brown spots and appear to change to hazel or brown later in life.
– Brown eyes may develop darker spots or concentric rings of deeper brown. The pupil may also appear to dilate less with age due to collapse of the iris surface architecture.
– The limbal ring at the edge of the iris may fade with age.
These subtle age-related shifts in iris color happen very slowly and are normal.
Other Causes of Eye Discoloration
Some other causes of eye color changes not related to the iris itself include:
Corneal Opacity
Scarring, injury, infection or deposits in the clear cornea can block light from entering the eye and make the overall eye appear darker or cloudy. Causes include:
– Corneal scars
– Keratitis infection
– Fuchs dystrophy
– Corneal tattooing procedures
Cataracts
With age, the lens inside the eye can become cloudy and discolored with cataracts. As cataracts develop, they can make the eye take on a yellow, brown or grayish hue. Cataract removal surgery is the treatment.
Vitreous Hemorrhage
Bleeding into the jelly-like vitreous inside the eye from injury or eye disorders makes the overall eye appear red or bloodshot. The bloody color persists until the vitreous hemorrhage is absorbed.
Eye Makeup
Cosmetic colored contact lenses, iris implants, or tattooing the sclera of the eye with ink can be done to deliberately alter eye color. These artificial cosmetic modifications are either temporary or permanent.
Diagnosing the Cause of Iris Heterochromia
If you notice one eye changing color or one eye looking different than the other, see an ophthalmologist (eye doctor) to determine the cause.
They will examine the eyes with a slit lamp microscope and use eye drops to dilate the pupils. Imaging tests might include:
– Photographs to document iris color, patterns and surface changes
– Ultrasound to look deeper at iris tissue and eye structures
– OCT scan to visualize the iris layers
– Fluorescein angiography to examine iris blood vessels
Based on the exam and imaging, the doctor can diagnose the type and cause of heterochromia. Eye freckles, Fuchs heterochromic iridocyclitis, cancer and other disorders can be identified.
Sometimes the reason for the color difference is not clear. Monitoring every 6-12 months may be recommended to ensure no worrisome changes.
Table of Differential Diagnosis of Heterochromia
| Cause | One or Both Eyes Affected | Onset and Progression | Other Symptoms |
|---|---|---|---|
| Heterochromia iridum | One eye only (usually) | Present from birth | None |
| Iris freckles | One or both eyes | Develops later in life, gradual | None |
| Fuchs heterochromic iridocyclitis | One eye (usually) | Gradual color change over months/years | Floaters, cataract, glaucoma |
| Medication side effects | One or both eyes | Begins after starting medication | None |
| Eye injury | One eye | Sudden after trauma | History of eye injury |
| Eye tumor | One eye | Gradual | Vision loss, eye pressure change |
| Aging | One or both eyes | Gradual lightening over decades | None |
Treatment for Abnormal Iris Color Changes
Treatment depends on the underlying cause:
– Heterochromia iridum – No treatment necessary since it is a benign congenital condition. Cosmetic contact lenses can be used if desired to make eye colors match.
– Eye freckles – Also benign so no treatment needed. Larger or suspicious looking iris nevi may be biopsied or removed.
– Fuchs heterochromic iridocyclitis – Topical corticosteroid eye drops to reduce inflammation. Treatments to prevent cataract and glaucoma.
– Medication side effects – Stop the medication causing discoloration or reduce dose. Color change may persist for months after stopping the drug.
– Eye injury – No treatment to reverse trauma-induced color defects. Surgery may remove disfiguring iris scars.
– Eye tumor – Treated based on tumor type which may include radiation, laser, surgery, chemotherapy or biopsy.
– Aging – No treatment for gradual age-related color change which is not harmful.
Conclusion
Random or asymmetric color changes in one or both eyes are usually harmless effects of medications, benign iris tumors, normal aging or congenital conditions like heterochromia.
However, acquired iris discoloration that arises later in life can also indicate serious inflammatory disorders, trauma or cancers in the eye.
Seeing an ophthalmologist promptly when you notice a new difference in eye color will allow the cause to be determined. Treatment can then be directed at the underlying condition, if needed, to protect vision.
