Multiple congenital ocular anomalies

Veterinary advice should be sought before applying any treatment or vaccine.

Multiple Congenital Ocular Anomalies

Anterior Segment Dysgenesis, MCOA Syndrome

MCOA syndrome is a heritable eye disorder that predominately affects silver colored horses. Horses inherit MCOA syndrome as an incompletely dominant trait. 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.

Complications of MCCA

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
  • Cataracts
  • 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.


Appears "pop-eyed'
Cloudy eye
Abnormal position of the lens
Translucent, fluid filled cysts


  • History
  • Clinical Signs
  • Physical exam



Treatment of eye disorders

Scientific Research

General Overviews

Risk Factors

  • Genetics

Commonly Affected Breeds

Morgan iconRocky Mountain Horse icon