Pigment Dispersion Syndrome (PDS) is characterized by the abnormal release of melanin pigment granules from the back surface of the iris, the colored part of the eye. This pigment floats freely within the eye’s internal fluid, known as the aqueous humor. The loose pigment collects on various structures within the eye’s anterior chamber. PDS is often bilateral, affecting both eyes, and is a significant precursor to a specific form of secondary glaucoma.
Defining the Syndrome and its Mechanism
The mechanism of Pigment Dispersion Syndrome involves a mechanical rubbing action within the eye. The iris often has a concave configuration, meaning it bows backward toward the lens. Constant movement causes the iris’s back surface (the pigmented epithelium) to brush against the zonules, the fibers holding the lens in place. This friction, occurring naturally with pupillary movement, sheds microscopic pigment granules into the aqueous humor.
These melanin granules are carried by fluid currents throughout the anterior chamber. A characteristic sign of this pigment dispersion is the Krukenberg spindle, a vertical deposition of pigment adhering to the inner surface of the cornea. The most problematic site of deposition is the trabecular meshwork, a sieve-like structure responsible for draining the aqueous humor out of the eye. Pigment accumulation here significantly impedes the eye’s natural drainage system, leading to complications.
Risk Factors and Who is Affected
PDS typically presents in young to middle-aged adults, generally between the ages of 20 and 40. Males are disproportionately affected and have a higher propensity to develop glaucoma compared to females. The syndrome also shows a higher prevalence among individuals of Caucasian descent.
PDS is strongly associated with high myopia, or nearsightedness. Myopic eyes often possess a deeper anterior chamber and the concave iris configuration. This configuration facilitates friction between the iris and the lens zonules. A family history suggests a genetic predisposition, with cases sometimes following an autosomal dominant inheritance pattern.
The Progression to Pigmentary Glaucoma
Pigment Dispersion Syndrome carries a substantial risk of progressing to Pigmentary Glaucoma (PG). This transition occurs when pigment clogging the trabecular meshwork compromises its function. The impaired drainage causes the intraocular pressure (IOP) within the eye to rise significantly, a condition known as ocular hypertension.
Sustained elevation of IOP damages the delicate nerve fibers of the optic nerve, leading to Pigmentary Glaucoma. This damage is progressive and results in irreversible loss of peripheral vision, which can advance to central vision loss if left untreated. The distinction between PDS (the syndrome) and PG (the resulting disease) is important for clinical management. Approximately one-third of individuals with PDS will eventually develop this form of secondary glaucoma.
Symptoms, Diagnosis, and Initial Management
Many people with PDS are asymptomatic. Some individuals may experience transient episodes of blurred vision or see colored halos around lights following strenuous exercise. These temporary symptoms result from a sudden “pigment shower,” where physical activity increases pigment release and causes a short-lived spike in IOP.
Diagnosis is primarily made by an ophthalmologist using specialized tools. Gonioscopy is a necessary procedure that allows the eye doctor to directly visualize the drainage angle and confirm the heavy, uniform pigmentation of the trabecular meshwork. Other findings include the Krukenberg spindle and characteristic spoke-like defects in the peripheral iris, visible with transillumination. Intraocular pressure is measured with tonometry. If glaucoma is suspected, a visual field test assesses for peripheral vision loss, while optical coherence tomography (OCT) evaluates the optic nerve head for damage.
Initial management of PDS without elevated IOP involves close, regular monitoring for the onset of ocular hypertension or glaucoma. If IOP begins to rise, treatment typically starts with prescription eye drops to help lower the pressure and protect the optic nerve. A laser procedure known as laser peripheral iridotomy may also be performed. This involves creating a small opening in the iris to equalize pressure between the chambers, causing the iris to flatten and reducing the mechanical rubbing that causes pigment release.