Primary lens luxation is an inherited abnormality of the eye affecting Jack Russell terriers. It is characterized by dislocation of the lens in the eye due to the breakage of the ligaments (called zonules) that hold the lens in place. The age of onset is variable depending on whether a dog has one or two copies of the Mutation, but affected dogs typically present between 2 to 8 years of age with sudden signs of eye irritation. Symptoms of lens luxation include excessive blinking, squinting and tearing of the eye. Dislocation of the lens can occur in both the forward and backward position within the eye, but dislocation in the forward position is more common and serious. If not treated immediately, lens dislocation can lead to Glaucoma and vision loss.