In pigment dispersion syndrome, pigment is liberated from the iris pigment epithelium and is deposited throughout the anterior segment. The classic diagnostic triad consists of a Krukenberg spindle, slit-like, mid-peripheral, radial iris transillumination defects and pigment deposition on the trabecular meshwork. The iris tends to have a concave configuration on gonioscopy (bowed posteriorly) and its insertion is typically posterior. Myopia is often present. Mechanical rubbing between the concave posterior iris surface and anterior zonular bundles is responsible for the loss of iris pigment and for the iris transillumination defects. A pressure gradient from the anterior chamber to the posterior chamber is thought to be responsible for the concave iris configuration. Ultrasound biomicroscopy is the only way to fully assess the extent of the iris concavity.
Laser iridotomy can eliminate reverse pupillary block present in this disorder by allowing free movement of aqueous between the anterior and posterior chambers. This causes the iris to flatten. Miotics, such as pilocarpine, produce relative pupillary block and a convex configuration. Both therapies increased iridozonular distance and may play a role in the disease process.
Mid-peripheral, radial, slit-like, iris transillumination defects in pigment dispersion syndrome. The pattern of pigment loss from the iris pigment epithelium is visible during retroillumination or transillumination of the globe.
Dense, homogeneous pigmentation of the trabecular meshwork in pigment dispersion syndrome.
Concave Iris Configuration in Pigment Dispersion Syndrome
In untreated pigment dispersion syndrome, the iris has a concave, or posteriorly bowed, configuration due to the greater pressure within the anterior chamber.
Laser iridotomy allows equilibration of the abnormal pressure gradient present in these eyes by allowing for free communication and flow of aqueous between the anterior and posterior chambers. Following laser iridotomy, the pressure gradient across the iris is eliminated and it assumes a flat (planar) configuration.
Accommodation and Iris Configuration
An increase in the iris concavity can be induced during accommodation (right) when compared to the non-accommodative state (left).