Pigment Dispersion Syndrome

Definition: Pigment dispersion syndrome is characterized by the deposition of iris pigment on the cornea endothelial surface, trabecular meshwork, anterior iris, lens capsule and lens zonule sometimes in association with glaucoma (½ of cases the cases of pigment disperstion syndrome).
History: Sugar and Barbour described pigment dispersion syndrome in 1949.
Incidence/ Prevalence: Pigment dispersion syndrome is associated with myopia, male gender, begins between the ages of 20-45 years, with a reported prevalence of up about ~2.5% in "whites", a population at risk. Familial cases are rare but are inherited in an autosomal dominant pattern. Glaucoma is present in 50% of the cases.
Etiology: In 1979 the concept was proposed that the iris bowed posteriorly in the midperiphery to rub against zonular fibers releasing pigment from the iris (1). The iris may have an irregular pupillary surface (#1 arrow in figure). The evidence for the zonular friction theory is that the anterior chamber in these patients is unusually deep in the midperiphery and that zonular fibers are found in proximity of the iris radial transillumination slits (# 2 red arrows in the gross photograph of the back of the iris). A reverse pupillary block mechanism has been invoked in which aqueous cannot flow into the posterior chamber because of the lens iris contact. The bowing may be worsened during forward movement of the lens as occurs during accommodation although increases in intraocular pressure and pigment dispersion with acccomodation are more controversial.
Pigment dispersion may be associated with a variety of other conditions in which pigment epithelium or uveal melanocytes are injured, such as uveitis (uveitic glaucoma) or uveal melanoma. These conditions are characterized by pigment within the trabecular meshwork and in macrophages littering the angle. The dispersed pigment is presumed to be iris pigment epithelium mechanically rubbed off by contact with lens zonular fibers.
Clinical Findings: There is a mid peripheral iris transillumination defect, iridonesis pigmentation anterior iris surface. Pigmentation on the posterior corneal surface is called Krukenberg’s spindle. There can be pigmentation of the lens (arrow #3), trabecular meshwork, pars plana.The pigmentation may precede the glaucoma by as much as 20 years.

Gross and Histopathology: Pigment is present on the lens zonule (arrow #4 above). Extracellular pigment becomes trapped in the trabecular meshwork (arrow #5). Scattered pigment may be seen lying on the anterior surface of the iris (arrow #6).Intracellular pigment may be found in macrophages lining the uveal cords and/or in endothelium lining the meshwork. Deposition of pigment tends to be mainly inferior on the cornea (arrow #5). Krukenberg’s spindle manifests histologically as pigment laden endothelial cells (arrow 7).
Treatment: Some believe that laser iridotomy may relieve the reverse pupillary block mechanism and reverse the posterior bowing of the iris. A decrease in pigment granules dispersed after laser has been published (2).
References:
1. Campbell DG. Pigmentary dispersion and glaucoma. A new theory. Arch Ophthalmol. 1979;97:1667-72.
2. Küchle M, Nguyen NX, Mardin CY, Naumann GO. Effect of neodymium:YAG laser iridotomy on number of aqueous melanin granules in primary pigment dispersion syndrome.
Graefes Arch Clin Exp Ophthalmol. 2001; 239:411-5.
3. Ritch R et al. Prevalence of pigment dispersion syndrome in a population undergoing glaucoma screening. AJO 1993:115:707.