Many systemic diseases may affect the eye and often the first sign of a systemic disease occurs in the eye. When discussing
ocular manifestations of systemic disease (OMSD) with clients broad categories may be used such as metabolic, neoplastic and
infectious since the majority of diseases that we see fall into these categories. Most textbooks use more detailed etiologic
divisions to include congenital, developmental, acquired, neoplastic, nutritional, toxicity, and miscellaneous.
Congenital anomalies are not that common in the general dog and cat population. The ocular abnormality and deafness associated
with white coat color is one form of congenital abnormality. The dwarfism noted in Labrador retrievers and Samoyeds is another;
this is also associated with ocular abnormalities. Hydrocephalus in both dogs and cats may result in deviation of the globes
in a ventrolateral direction and rarely may elicit papilledema.
Developmental diseases include tyrosinemia which is an inborn error of intermediary metabolism. Lysosomal storage diseases,
consisting of ceroid lipofuscinosis, fucosidosis, galactocerebrosidosis, gangliosidosis, and mucopolysaccharidosis, are very
uncommon. Ceroid lipofuscinosis is seen in both dogs and cats. Tibetan terriers and English setters tend to be affected as
adults, with Tibetan terriers experiencing a late onset. Decreased vision, especially in dim light is one of the presenting
signs. Other behavioral abnormalities follow. ERG testing reveals decreased retinal activity although the waveforms are not
flat. Histopathology reveals retinal abnormalities and cellular inclusions. At this time there is no treatment.
Acquired diseases are the most common type of OMSD. Hypertension often presents with blindness as the first abnormal sign.
The hemorrhage and, with progression, retinal detachment seen with hypertension results from vasoconstriction, followed by
vessel occlusion and ischemia. Subretinal fluid may develop leading to retinal detachments. Primary and secondary etiologies
may occur; renal disease, hyperadrenocorticism, pheochromocytoma, primary aldosteronism, hypothyroidism, and hyperthyroidism
are all possible etiologies. Intraocular hemorrhage or effusive retinal detachments should include a blood pressure as part
of the diagnostic plan. Treatment is focused on treating the hypertension as well as the underlying cause. Even when the primary
disease is treated anti-hypertensive medications may still be necessary as part of the long term treatment plan.
Thrombocytopenia may lead to ocular changes. Infectious disease, neoplasia, drug-induced reactions, and immune-mediated disease
are all common etiologies. Infectious diseases include arthropod-borne organisms: Babesia, Borrelia, Cytauxzoon, Dirofilaria, Ehrlichia spp., Leishmania, Rickettsia, etc.; viruses, including canine distemper virus, herpesvirus, parvovirus, adenovirus; fungal and bacterial organisms, including
Candida, Histoplasma, Leptospira spp., etc. Neoplastic etiologies include lymphoma, leukemia, and multiple myeloma. Medications that impair platelet production
or lead to platelet destruction include chloramphenicol, azathioprine, cyclophosphamide, doxorubicin, etc. Thrombocytopenia
may present as both periocular and intraocular hemorrhage and petechiation. Therapy is directed at the underlying cause.
Other hematologic diseases with possible ocular involvement include anemia, hyperlipidemia, hyperviscosity syndrome, icterus,
intravenous fluid overload, and polycytemia. Anemia may be associated with pale retinal vasculature and retinal hemorrhages.
The pathogenesis of the hemorrhages may be from vessel wall hypoxia resulting from the anemia. In cats, FeLV infection may
be associated with anemia and retinal hemorrhages. Mycoplasma haemofelis infection may also lead to anemia in cats. Hyperlipidemia may be associated with lipid-laden retinal vasculature, lipid-laden
aqueous uveitis, lipid keratopathy and corneal arcus lesions. Work-up should include fasting CBC and Chemistry, urinalysis
and thyroid panel. A dietary history is also important in diagnosis and treatment. Treatment is planned based on diagnostic
testing results. Hyperviscosity syndrome and polycythemia may lead to retinal detachments, hemorrhage and uveitis. Treatment
is described in many internal medicine texts. Icterus may lead to changes in iris and tapetal coloration. Lastly, i.v. fluid
overload may be associated with bullous retinal detachments which resolve once the fluid overload is addressed.