Eye disorders can occur because of diseases affecting other parts of the body. They can occur with inherited, infectious, degenerative, and cancerous disorders. Often, discovering a change in the eyes can help uncover the systemic disorder sooner than if eyes had not been examined. Diseases affecting the blood vessels or nervous system are likely to produce changes in the eyes. If your dog has a disease that affects both eyes, your veterinarian will often look for diseases in the rest of the body.
In dogs, eye diseases, such as retinal dysplasia, small eye size (microphthalmia), and cataracts, have been associated with other types of birth defects. Infections by viruses, bacteria, fungi, protozoa, algae, or parasites can cause inflammation of the eye. Metabolic diseases associated with eye diseases in the dog include diabetes, low blood calcium levels, Cushing disease, and low thyroid levels (hypothyroidism). Blood and blood vessel disorders and metastatic cancer can also show signs in the eyes.
Also see professional content regarding ophthalmic manifestations of systemic diseases Ophthalmic Manifestations of Systemic Diseases in Animals Ophthalmic manifestations can occur with inherited, infectious, degenerative, parasitic, toxic, nutritional and neoplastic disorders in animals. Often, ophthalmic examinations can assist in... read more 
.
