Heterochromia - Causes, Types, Manifestations, and Management

What Do You Mean by Heterochromia of the Eye?

Heterochromia is defined as the difference in color in the two eyes' iris. It is also known as heterochromia iridium. The eye color changes initially after birth, with the maximum number of changes occurring between three to six months after birth. In patients suffering from heterochromia, the color of the eyes remains different.

What Is the Iris of the Eye?

The eye's iris is the pigmented component between the transparent part of the eye (cornea) and the lens. The iris comprises two layers; the anterior layer of the iris or the iris stroma. It consists of the pupillary sphincter, blood vessels, and nerves, while the posterior layer is the pigmented epithelium layer. The stromal layer of the iris contains melanocytes that produce melanin.

What Is the Mechanism Involved Behind Eye Color?

The color of the eyes depends mainly on the melanin produced by the melanocytes in front of the iris. The color of the eye color depends on the amount, type, and location of the melanin pigment.

There are mainly two types of stain:

• Eumelanin is responsible for the brown to black color of the eyes.

• Pheomelanin imparts red to yellow color to the eyes.

Genes also play an essential role in determining eye color. Brown is the most dominant color, followed by green and blue.

How Common Is Heterochromia?

The incidence of acquiring heterochromia of the eyes is significantly less, it mostly occurs in association with some other disease. Therefore, heterochromia is a rare condition of the eyes.

What Are the Causes That Are Associated With Heterochromia of the Eyes?

Heterochromia of the eyes can be caused by congenital and acquired factors.

1. Congenital Causes That Cause Heterochromia Are:

• Horner's syndrome.

• Parry-Romberg syndrome.

• Sturge-Weber syndrome.

• Neurofibromatosis I.

• Iris ectropion syndrome.

2. Acquired Causes That Cause Heterochromia Are:

• Neuroblastoma.

• Trauma.

• Foreign body in the eye.

• Contact lenses.

• Iris tumors.

• Prostaglandin eye drops.

What Are the Factors That Are Linked to Color of the Eye?

Several factors contribute to the heterochromia of the eye. These factors are:

• Injury or trauma to the iris also leads to a difference in eye color.

• The difference in the size of the pupil also contributes to heterochromia.

• The presence of benign tumors in the iris causes heterochromia.

• Lighting conditions also affect the color and affect the appearance of the eye.

• Optical phenomena like Rayleigh and Tyndall scattering also play a vital role in developing heterochromia of the eye.

What Is the Mechanism Involved Behind the Development of Heterochromia in the Eyes?

The color of the eyes depends on the amount of melanin produced and the number of melanocytes present in the iris's stroma. In turn, the iris stroma is governed by the sympathetic nervous system. Any lesion or condition disrupting the sympathetic supply to the iris leads to heterochromia. Diseases of the melanocyte of the iris also cause heterochromia. For example, in patients suffering from Horner's syndrome before the age of two, the color of the iris in the affected eye is lighter than the normal eye.

What Are the Different Types of Heterochromia?

Heterochromia of the eyes is mainly categorized into three types:

• First, complete heterochromia of the eye is characterized by the complete change in color between the two eyes.

• Second, partial heterochromia is defined as a change in the color iris along the outer borders of the pupil. It is the most common type.

• Thirdly, the sectoral or segmental heterochromia. It affects most of the iris. It clinically manifests as an irregular spot on the iris of the eyes.

What Are the Clinical Manifestations of the Heterochromia of the Eye?

The main clinical feature of heterochromia of the eye is the presence of differences in eye color. The change in the eye color may be present from birth, or it may occur gradually with the acquisition of other diseases.

What Are the Different Methods Used to Diagnose People With Heterochromia?

Patients suffering from heterochromia are diagnosed based on their history and clinical examination of the eye. Isolated or benign cases of heterochromia are diagnosed clinically.

• Complete history, including the onset, duration, trauma history, presence of any other ocular symptoms, and medical history, are acquired from the patients.

• The slit-lamp technique conducts the physical evaluation of the iris and the surrounding structures of the eye. Ophthalmologists mainly look for signs of Horner's syndrome.

• Computed tomography (CT) of the chest and abdomen and urinary catecholamine administration is performed in children and infants to rule out Horner's syndrome.

• CT angiogram is done to investigate the internal carotid artery in congenital Horner's syndrome.

What Are the Different Approaches Used in Treating Heterochromia of the Eyes?

Heterochromia is a sign, not a disease. Hence the treatment approaches followed are aimed at treating the underlying cause. Congenital heterochromia does not require any treatment.

Some patients can opt for colored contact lenses to improve their esthetics.

What Are the Conditions That Present Clinically With Heterochromia of the Eyes?

Since heterochromia of the eye is a clinical sign, many conditions present with similar clinical manifestations. Conditions presenting with heterochromia of the eye include:

• Isolated heterochromia.

• Congenital Horner's syndrome.

• Iris and ciliary body inflammation (iridocyclitis).

• Fuchs heterochromic iridocyclitis.

• Melanoma.

Can Heterochromia Lead To Any Complication of the Eye?

Isolated or benign heterochromia is a clinical sign. It does not cause any complications. However, if the heterochromia is associated with another condition, the underlying tumor or lesion can cause further complications in the eye. For example, Fuchs iridocyclitis can cause glaucoma.

What Is the Prognosis of Heterochromia of the Eyes?

The prognosis of heterochromia depends on the underlying cause. In the case of lesions or tumors affecting the sympathetic chain, or congenital Horner's syndrome in children and infants, the prognosis of the condition is poor. For example, Fuch's iridocyclitis is also a vision-threatening condition. On the other hand, isolated heterochromia has an excellent prognosis.

Conclusion

Heterochromia iridum of the eye is a rare and benign condition of the eye. Isolated cases of the state do not cause any severe complications. However, there is a need to determine any inapparent cause of the disease. An ophthalmologist referral is needed to manage the associated conditions. Overall, heterochromia enjoys an excellent prognosis.