Latanoprost is a medication primarily prescribed to manage elevated intraocular pressure, a common factor in conditions like open-angle glaucoma and ocular hypertension. This medication works by increasing the outflow of fluid from the eye, which helps to lower the internal pressure. Latanoprost is also known for a notable side effect: the potential for a gradual and permanent change in eye color. This phenomenon is a recognized characteristic of the drug, leading many individuals to seek understanding about how and why it occurs.
The Mechanism of Iris Color Change
Latanoprost is a prostaglandin F2-alpha analog, a synthetic compound resembling naturally occurring prostaglandins. These analogs interact with specific receptors within the eye, particularly on melanocytes in the iris stroma. Melanocytes are specialized cells that produce melanin, the pigment determining eye color.
The drug stimulates melanogenesis, increasing the production of eumelanin, the brown-black pigment responsible for darker eye colors. This stimulation does not typically cause melanocyte proliferation, but rather enhances the activity of existing cells, increasing their melanin content. The increased melanin density within the iris tissue causes the eye to appear darker.
What to Expect From the Color Change
The eye color change induced by latanoprost primarily affects individuals with mixed-color irises, such as green, hazel, blue-brown, gray-brown, or yellow-brown. Pure brown eyes rarely show a noticeable darkening, and pure blue eyes are less likely to change compared to mixed-color eyes. The alteration is a gradual darkening rather than a complete transformation of color.
Patients may observe brown spots developing in the iris periphery, slowly spreading over time. For instance, blue or green eyes might develop these brown areas, eventually appearing more hazel or light brown. This change typically begins within the first year of treatment, often around 8 months, but can continue to progress for several years. The resulting color change is permanent and does not reverse, even if the medication is discontinued. If treatment is unilateral, the change generally affects only the treated eye, leading to a difference in color between the two eyes.
Likelihood and Other Related Effects
The incidence of iris color change due to latanoprost varies across studies, with reported rates ranging from approximately 10.8% to 22.9%. Higher prevalence in some studies may be attributed to a greater proportion of patients with mixed-color irises, which are more susceptible. This color change is a cosmetic side effect and is not associated with harm to eye health or vision.
Beyond iris darkening, other common cosmetic side effects with prostaglandin analogs like latanoprost include changes to the eyelashes and eyelid skin. Many patients experience hypertrichosis (lengthening, thickening, and darkening of eyelashes). Additionally, darkening of the eyelid skin, known as periocular hyperpigmentation, can occur. While iris color changes are permanent, changes in eyelash and periocular skin pigmentation may be reversible if the medication is stopped.