When you think of systemic diseases that you’ll encounter as a vet, you probably envision diagnosing those conditions on the basis of a thorough physical exam, screening blood tests, and other body-wide diagnostics. In some cases, however, a thorough ophthalmologic exam will be all that is needed to provide you with a strong suspicion of a systemic disease. 

While there are many systemic diseases that may present with ocular manifestations, these 7 conditions should always be on your radar when dealing with unexpected ocular disease.

1. Diabetes Mellitus

Approximately 60% of dogs that are diagnosed with diabetes mellitus have cataracts at the time of diagnosis.⁽¹⁾ This makes diabetes mellitus the canine systemic disease that most commonly presents with ocular manifestations. When you see a dog with a recent onset of cataracts, think diabetes. Cats, in contrast, rarely develop cataracts with diabetes; cataracts in cats are typically caused by other factors.⁽²⁾

The development of diabetic cataracts in dogs may be accompanied by a number of additional ophthalmic abnormalities. Affected pets may develop lens-induced uveitis (a common sequela of cataracts), as well as other issues such as corneal endothelial abnormalities, tear film abnormalities, and retinal vascular damage.⁽¹⁾ 

2. Hypertension

Hypertension is another common cause of ocular disease, especially in cats. In many cats, the sudden onset of blindness is the first sign of systemic hypertension, caused by retinal detachment.⁽¹⁾  When an older cat presents for an acute onset of blindness, assess the cat’s blood pressure.

Other signs of hypertension that may be noted on ophthalmic exam include tortuous retinal vessels, optic nerve edema, and retinal/vitreal hemorrhage.^(1,2) Retinal degeneration may also occur, caused by retinal ischemia and inflammation.⁽²⁾

3. Cushing’s Disease

Cushing’s disease in dogs is associated with a number of ophthalmologic abnormalities, including corneal abnormalities (such as corneal degeneration and ulceration), keratoconjunctivitis sicca, lipemia of the aqueous humor and/or retina, and hypertensive chorioretinopathy.⁽²⁾ While none of these conditions are diagnostics for Cushing’s, you may want to consider Cushing’s in dogs with multiple ocular abnormalities and other supporting clinical signs. 

Dogs with Cushing’s disease are also at a higher risk of developing sudden acquired retinal degeneration syndrome (SARDS).⁽²⁾ Therefore, the possibility of Cushing’s disease should be considered in any dog presenting for SARDS.

4. Hypothyroidism

Dogs with hypothyroidism are prone to lipidemia.⁽²⁾ Elevated circulating lipid levels can lead to a number of ocular abnormalities, caused by lipid deposition within the eye. Lipids may deposit on the cornea (causing corneal lipidosis), in the anterior chamber (causing aqueous lipidosis), or within the retinal vessels (causing lipemia retinalis).⁽³⁾

Additionally, dogs with hypothyroidism are predisposed to retinal hemorrhage, retinal detachment, and nonhealing corneal ulcers.⁽²⁾

5. Tick-Borne Diseases

Tick-borne diseases are associated with a number of ocular manifestations, most commonly observed in dogs. Up to 37% of dogs with ehrlichiosis develop ocular signs, which may include uveitis, chorioretinitis, and optic neuritis.⁽¹⁾  Anaplasmosis is associated with steroid-responsive uveitis, while Rocky Mountain Spotted Fever is typically associated with conjunctivitis, chemosis, uveitis, hyphema, and retinal edema/vasculitis.⁽¹⁾ 

The effects of tick-borne disease on the eye are largely caused by vasculitis and thrombocytopenia. Tick-borne disease should be considered in any pet with inflammatory eye disease. These eye lesions typically resolve with doxycycline treatment.⁽¹⁾ 

6. Feline Immunodeficiency Virus, Feline Leukemia Virus

If you think that feline herpes virus is the only virus that causes eye lesions in cats, you are incorrect. While herpes is certainly the most common viral cause of feline ocular disease,⁽¹⁾ other viruses can also play a role. 

Feline immunodeficiency virus can cause a number of eye lesions in infected cats, including conjunctivitis, uveitis, and precipitates on the lens and in the vitreous.⁽¹⁾  Feline leukemia virus, in contrast, is often associated with spastic pupil syndrome and anisocoria; kittens born with feline leukemia may also have retinal dysplasia and diffuse uveitis.⁽¹⁾  In FeLV-infected cats that go on to develop lymphoma, lymphocytes may spread into the eye and lead to uveitis and secondary glaucoma.⁽¹⁾ 

7. Toxoplasmosis 

Up to 79% of cats with uveitis are seropositive for Toxoplasma gondii.⁽²⁾ Although the organism is rarely isolated within the uvea, both dogs and cats with toxoplasmosis are predisposed to ocular abnormalities that are thought to be associated with the immune response to this organism.

While cats with toxoplasmosis may present for chorioretinitis, dogs may develop additional signs such as scleritis, uveitis, retinitis, choroiditis, optic neuritis, and extraocular myositis.⁽¹⁾ 

Although it is rarely possible to diagnose a systemic disease based solely on an ophthalmic exam, it’s important to keep these systemic diseases in mind as you evaluate your patients for ocular disease! 

References

1. Hyman, J. 2009. Ocular Manifestations of Systemic Diseases. DVM360. 
2. Kaese, H. 2013. It’s All in the Eyes: A Look at Ocular Signs of Disease. DVM360.
3. Fife, T. 2011. Ocular Manifestations of Systemic Disease - When the Eye is Not the Primary Disease.