Equine Multiple Congenital Ocular Anomalies (MCOA) syndrome is a heritable eye disorder that predominately affects silver colored horses. Extensive breeding of horses for their desirable silver coat color has lead to a high frequency of MCOA syndrome in the Rocky Mountain horse breed. This silver coat trait is characterized by the dilution of black pigment in the horse's hair and is most visible in the mane and tail. Cases of MCOA have also occurred also in other horse breeds--Icelandic Horse, Shetland Pony, Exmoor Pony, American Miniature Horse, Belgian Draft and Morgan Horse, Kentucky Mountain Saddle Horse, and the Mountain Pleasure Horse.
Horses inherit MCOA syndrome as an incompletely dominant trait. Horses with the MCOA-phenotype are at particular risk of developing a number of eye anomalies, including, but are not restricted to:
- Uveal cysts
- Cornea globosa
- Iris stromal hypoplasia
- Abnormal pectinate ligaments
- Iris hypoplasia
Horses may suffer from impaired vision, and difficulties in adapting to changing light conditions. Some individuals have more severe impairment of their vision, causing abnormal behavior and an inability to perform.