Before and After Latanoprost Eye Color Change: What to Expect

Latanoprost, a medication for glaucoma and ocular hypertension, has an unusual side effect—gradual eye color changes. This occurs due to increased melanin production in the iris, leading to a darker appearance over time. While harmless, the change is irreversible and may concern some individuals using or considering the medication.

Mechanism Of Iris Pigment Alteration

Latanoprost, a prostaglandin F2α analog, alters iris color by stimulating melanogenesis within stromal melanocytes. Unlike other pigmentation processes that involve melanocyte proliferation, this medication enhances the activity of existing melanocytes, prompting them to produce more melanin. This results in a gradual darkening, particularly in individuals with mixed-color irises, such as green-brown or blue-brown combinations.

The drug interacts with prostaglandin receptors, specifically the FP receptor subtype in ocular tissues. Activation of these receptors upregulates tyrosinase, a key enzyme in melanin biosynthesis, increasing melanin production. This effect is most pronounced in the anterior iris stroma, where melanocytes are more responsive to prostaglandin signaling.

Histological studies confirm that latanoprost-induced pigmentation is localized rather than systemic. Biopsies show a higher density of melanin granules within iris melanocytes without inflammatory infiltration or structural damage. Electron microscopy further demonstrates an increase in mature melanosomes, reinforcing that latanoprost enhances pigment production rather than altering cellular composition.

Timeline And Extent Of Color Change

Iris pigmentation changes with latanoprost occur gradually over months to years. Clinical data indicate that noticeable changes typically appear within three to six months of continuous treatment, though subtle shifts may begin earlier. The rate and degree of pigmentation vary based on baseline iris composition, treatment duration, and individual melanocyte responsiveness.

Longitudinal studies show the darkening effect is most pronounced in the first year, then slows. A study in Ophthalmology found that after 24 months, about 33% of individuals with mixed-color irises exhibited noticeable darkening. The process eventually plateaus, suggesting a saturation point in melanin production.

The color shift is not uniform across the iris. Darkening often begins around the pupillary margin before extending outward. High-resolution imaging shows the peripupillary region darkens first, likely due to a higher prostaglandin receptor density. Over time, pigmentation may spread evenly or remain mottled, depending on the original iris structure. Blue or gray eyes, with lower melanin content, are far less susceptible to these changes, while green-brown or hazel irises are most affected.

Differences Among Baseline Eye Shades

Latanoprost’s impact on eye color depends on baseline pigmentation. Hazel or green-brown irises experience the most noticeable darkening due to the presence of both eumelanin and pheomelanin. Under latanoprost treatment, eumelanin increases, overshadowing lighter pheomelanin tones and leading to a deeper brown hue.

In contrast, blue and gray eyes, which contain minimal melanin, show little to no response. Their coloration results from light scattering rather than melanin deposits, making any pigment increase negligible. Clinical observations confirm that patients with purely blue irises rarely report visible changes.

Brown irises, already rich in eumelanin, exhibit minimal change. While some individuals may notice a slight deepening of their eye color, the difference is often subtle. The most apparent transformations occur in those with lighter brown or mixed-color irises, where increased melanin density shifts the balance between shades, making the eye appear darker overall.

Reported Patterns In Clinical Observations

Ophthalmologists have documented distinct trends in latanoprost-induced iris pigmentation. Early stages may present asymmetrically, especially in individuals who started treatment in one eye before using it bilaterally. This can result in noticeable differences in iris coloration, which persist even after both eyes are treated.

Photographic comparisons from clinical trials show pigmentation changes are not uniform across the iris. High-resolution imaging and anterior segment optical coherence tomography (AS-OCT) scans reveal that darkening often begins in the peripupillary region before radiating outward. The outer periphery may retain more of its original hue, creating a gradient effect that varies depending on baseline eye color and individual responsiveness.