Incomplete Maturation of Iridal Pigment in Heterochromia Iridum

Abstract

Heterochromia is an abnormality of iridal pigmentation characterized by marked differences in the color of the two irides or in segments of one iris. The affected areas are pale blue to grayish white. The condition is known to be present in a variety of species including man, dog, mouse, rabbit, cat, pig, and horse. In some species heterochromia has been transmitted as an autosomal dominant trait. It is also a dominant characteristic in Waardenberg's oculo-dermato-auditive syndrome. In several breeds of dogs heterochromia is associated with merle (or harlequin or dappled) coat color which is controlled by an autosomal dominant gene. Other factors are involved in Fuch's heterochromic cyclitis.The present study resulted from the spontaneous occurrence of 5 cases of heterochromia in a large colony of beagles produced to study the long-term effects of low doses of radiation administered at various ages. When ten weeks old (3 or 4 weeks after the dog eye has attained adult characteristics), the affected dogs were anesthetized with pentobarbital sodium. The eyes were extirpated and quickly hemisected dorsoventrally. One calotte was fixed in cold glutaraldehyde-acrolein for 90 minutes. Representative blocks through the iris were cut and stored in phosphate buffer (pH 7. 3) overnight, washed in veronal-acetate buffer, pH 7.3, and post-fixed in 2% OsO4 in veronal-acetate buffer. Further processing was by standard techniques. The sections were stained with uranyl acetate and lead citrate. The other calotte was fixed for 24 hours in 6.25% glutaraldehyde for light microscopy. The calotte was rinsed in phosphate buffer, pH 7.3., embedded in paraffin, sectioned at 6μ and stained with hema-toxylin and eosin.