Occasionally chickens can either hatch blind or without eyes, or can go blind as a result of disease or injury to one or both eyes. Like with people, blindness can make things more challenging, however there are many blind chickens who are able to live happy, healthy lives. Chickens that are born with or acquire disabilities should not be so quickly cast aside---as there are many people who have kept and continued to care for blind chickens.
Diseases associated with blindness in chickens include:
How to tell if a Chicken is Blind
- Avian encephalomyelitis: Avian encephalomyelitis (AE) is an important infectious disease affecting young chicks that is reported to be fairly common in backyard chickens. The disease is caused by the picornavirus, avian encephalomyelitis virus (AEV). Chicks that recover from AE have an increased risk of developing cataracts later in life resulting in blindness in one or both eyes.
- Marek's disease: Marek’s disease is one of the most common diseases found in backyard chicken flocks worldwide. MD is caused by Marek's disease virus (MDV), or Gallid herpesvirus 2 (GaHV-2) and presents as several different forms. One form, referred to as the Ocular (eye form), can cause chickens to develop gray, often misshapen, shrunken or unequally-shaped pupils that progress to blindness in one or both eyes.
- Chronic sinusitis: Chickens which develop chronic sinusitis (inflammation of the infraorbital sinuses) have a high risk of developing 'sunken sinus' which is where the globe of the eye retreats into its socket, giving the chicken the appearance of 'losing its eye', which can often result in blindness without proper treatment.
One of the most obvious, externally obvious clinical signs that a chicken is likely blind is the appearance of a gray or bluish cloudy eye color and irregularly shaped pupil. When only one eye is affected, the pupils are often different sizes as well. A quick and easy test that can be performed, to check whether a chicken is blind, is to slowly (don't use rapid movements because otherwise they can feel the airflow and sense the motion) move your finger towards the affected eye. A chicken that does not blind or try to move out of the way is likely blind.
In 2006, University of Florida scientists developed a gene therapy that helped restore sight to chicks with a certain genetic defect that were usually born blind. The genetic defect was associated with the Rhode Island Red chicken breed, that carry a defect preventing them from producing an enzyme essential for site. The condition is very similar to Leber congenital amaurosis type 1, or LCA1, a genetic defect in humans that causes blindness.