Distribution and amount of pigment within the ciliary body and iris of dogs with blue and brown irides.

OBJECTIVE

Compare the amount and distribution of pigment in normal canine eyes with blue and brown irides.

ANIMAL STUDIED: Eighteen mixed-breed dogs euthanized for population control.

PROCEDURES: Intact globes were removed immediately following euthanasia. Iris color was noted, and globes were evaluated histologically to determine the distribution of pigment. High magnification (x400) digital images were taken of the dorsal and ventral ciliary processes (CP) of 13 eyes with blue irides and 13 eyes with brown irides. Low magnification (x20) images were taken of the dorsal and ventral portions of the ciliary body (CB) of 14 eyes with blue irides and 14 eyes with brown irides. The images were digitally analyzed to determine the percent of the CP and CB that were pigmented in the high and low magnification images, respectively.

RESULTS

Eyes with brown irides contained abundant melanin pigment around the CB musculature. This pigment was absent in eyes with blue irides, and the difference was statistically significant (P = 0.001) when digitally analyzed using the low magnification images. Iris color did not have a significant (P = 0.34) impact on the amount of melanin within the CP, as determined using the high magnification images.

CONCLUSIONS

Compared to eyes with brown irides, eyes with blue irides lack pigment around the CB musculature, but contain comparable amounts of pigment in the CP.