Free-floating melanin particles in the anterior chamber: a normal finding in African eyes?

Purpose: Pigment dispersion syndrome (PDS) is a well-described entity with Krukenberg's spindle, heavy trabecular pigmentation and retroilluminating iris defects. We have observed a group of patients in mesoendemic onchocercal communities of Kaduna State, Nigeria, with significant amounts of free-floating melanin in the anterior chamber, normal angle pigmentation and absence of iris defects. A pseudo-Krukenberg spindle forms when the patients are asked to maintain a 2 min head-down posture as is often done when examining eyes for the presence of anterior chamber microfilaria. This spindle gradually disappears (tumbles back) after about 2 min of return to the erect posture. This paper describes this finding, which does not appear to fit into accepted notions of pigment dispersion.

Methods: As part of the seventh annual ivermectin dosing exercise during which evidence of optic nerve damage was sought, 455 patients were examined for the presence of microfilaria in the anterior chamber. A total of 352 had been selected for signs of optic nerve disease during an earlier screening exercise, while 103 belonged to a random sample of 5 years and above. Signs of onchocerciasis were sought, while gonioscopy and intraocular pressure measurements were carried out.

Results: Of the 455 (11%) individuals examined, 53 demonstrated this phenomenon. Within the random sample, the prevalence was 20%. These tumbling Krukenberg positive (TK+) individuals are significantly younger than TK- individuals and the prevalence, highest in the first decade, dropped steadily to zero levels over the age of 75. Sex distribution was about equal. There was no difference in intraocular pressure, cup-disc ratio and angle pigmentation. Distributions of sclerosing keratitis and chorioretinitis were not statistically different. Optic nerve disease was more common in TK- but this was attributable to the older age distribution. Five TK+ were re-examined after a period of 7 years and had not developed PDS or glaucoma. Four of the five remained TK+. A familial tendency was noted and hereditary factors may be at play, possibly autosomal recessive. The same phenomenon was noted in two of 44 patients in an ophthalmic clinic in Abuja, Nigeria, an urban, non-endemic city south of Kaduna.

Conclusions: This phenomenon does not fit into accepted notions of PDS and may well be a normal finding.