Pigment dispersion is a fascinating cause of secondary glaucoma; although relatively common, little is understood about its prevalence, and whether damage to the optic nerve can be prevented is unknown. The concept of pigment dispersion in the anterior chamber and its possible link to glaucoma was introduced around 1900, when Krukenberg first described the corneal endothelial pigment that bears his name, and Von Hippel proposed that pigment could obstruct aqueous flow. Over time, the condition came to be defined as a clinical syndrome characterized by pigment deposits on the corneal endothelium (Krukenberg spindle); radial, midperipheral transillumination defects of the iris (Figure 1A); and pigment deposition on the zonules (Scheie stripe) and in the trabecular meshwork (TM). By the mid-20th century, based on the observations of Sugar and Barbour, this syndrome was linked to increased IOP and glaucoma.1

In 1979, David G. Campbell, MD, proposed that pigment is released from the pigment epithelium of the iris when it rubs against the lens and zonules.2 This contact, Campbell argued, is brought about by a posterior bowing of the iris that is not present in most eyes (Figure 2A). Some of the pigment that is released makes its way to the TM and undergoes phagocytosis by the endothelial cells. In certain eyes, this endocytosed pigment does not cause trabecular dysfunction, whereas in others, the TM becomes disorganized and dysfunctional, causing the obstruction of aqueous flow.3

PREVALENCE

The prevalence of pigment dispersion and of pigmentary glaucoma has not been determined in populationbased studies. Ritch et al conducted two population screenings that included slit-lamp examination and detected a 2% to 3% prevalence of glaucoma dispersion in the United States.4 A retrospective study by Siddiqui et al found that the risk of developing pigmentary glaucoma from pigment dispersion syndrome was 10% at 5 years and 15% at 15 years.5

Given the nature of the studies that have looked at risk factors for pigment dispersion, it is not surprising that variability in these estimates exists. In general, however, although pigment dispersion is almost equally likely in men and women, men are two to five times more likely to be diagnosed with pigmentary glaucoma.6 Pigment dispersion is also more likely to be diagnosed in myopic eyes, although it has been found in eyes with a range of refractive errors.

TREATMENT

Like primary open-angle glaucoma, pigmentary glaucoma is managed with a combination of eye drops, laser trabeculoplasty, and incisional surgery. Laser trabeculoplasty should be performed with extra caution on eyes with pigmentary glaucoma due to the increased absorption of laser energy by the pigmented TM. There is also a theoretical reason to consider miotic agents to treat pigmentary glaucoma: miosis may overcome the tendency of the iris to bow posteriorly, thereby preventing the further release of pigment. There are significant downsides to this approach, however, including the induction of myopia and presbyopia in patients who are young and already myopic and the increased rate of retinal detachment in this population.

THE OPTIC NERVE

The potential to prevent optic nerve damage in eyes with pigment dispersion relates to the mechanism of the disease, which seems to be primarily mechanical in nature, suggesting that a surgical solution may be available. In eyes with pigment dispersion syndrome, the normally flat or convex iris (Figure 2B) becomes concave enough to come into contact with structures posterior to it (Figure 2A). In effect, the situation is one of reverse pupillary block in which the pressure anterior to the iris is at least transiently elevated relative to that posterior to the iris. There is evidence that this configuration may be induced both by blinking7 and by accommodation.8 Once the concept of (reverse) pupillary block is invoked, it makes sense to consider iridotomy as a potential way to prevent the abnormal backward bowing of the iris. Since the first iridotomies for pigment dispersion were performed in the early 1980s, there have been several case reports and relatively small case series documenting varying success in altering the configuration of the iris and preventing increases in IOP.9

The case represented in Figure 1 depicts a natural experiment in support of this approach. The patient's right eye has pigment dispersion, and the left eye has large iris defects due to iridocorneal endothelial syndrome and no signs of pigment dispersion. The best evidence available with regard to prophylactic iridotomy, however, is a randomized, controlled trial that found the approach did not prevent progression from pigment dispersion syndrome to pigmentary glaucoma 3 years postoperatively.10

CONCLUSION

Based on currently available information, the best approach to treat pigment dispersion syndrome is vigilance with regard to the clinical examination of patients. Those with the condition must be carefully monitored for elevated IOP and damage to the optic nerve. Future studies are needed to determine whether the abnormal iris configuration and consequent liberation of pigment can be prevented.

Michael V. Boland, MD, PhD, is an assistant professor and director of information technology at the Wilmer Eye Institute, Johns Hopkins University in Baltimore. Dr. Boland may be reached at boland@jhu.edu.

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  2. Campbell DG. Pigmentary dispersion and glaucoma. A new theory. Arch Ophthalmol. 1979;97(9):1667-1672.
  3. Richardson TM, Hutchinson BT, Grant WM. The outflow tract in pigmentary glaucoma: a light and electron microscopic study. Arch Ophthalmol. 1977;95(6):1015-1025.
  4. Ritch R, Steinberger D, Liebmann JM. Prevalence of pigment dispersion syndrome in a population undergoing glaucoma screening. Am J Ophthalmol. 1993;115(6):707-710.
  5. Siddiqui Y, Ten Hulzen RD, Cameron JD, et al. What is the risk of developing pigmentary glaucoma from pigment dispersion syndrome? Am J Ophthalmol. 2003;135(6):794-799.
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