Collie eye anomaly (CEA), also known as choroidal hypoplasia (CH), is an inherited disease affecting several dog breeds. The choroid is the layer of tissue in the eye responsible for supplying blood and nutrients to the retina. In dogs affected with CEA, the choroid does not develop properly and is therefore thinner than normal often leading to retinal detachment and subsequent blindness. The severity of the condition can vary from dog to dog. Mildly affected dogs may have thinning of the choroid with normal vision, while severely affected dogs may have additional eye problems, such as colobomas, retinal detachment, intraocular hemorrhage, and significant vision loss including complete blindness. Because both mild and severe forms of CEA are associated with the same NHEJ1 gene mutation, predicting the potential severity of the disease in an affected dog is difficult e.g., a mildly affected dog may produce offspring that are severely affected.