Manifestations of systemic disease in the retina and fundus of cats and dogs

“

TL;DR

This review catalogs retinal and fundic changes in cats and dogs that signal underlying systemic diseases, ranging from pathognomonic signs (e.g., lipemia retinalis, vitamin E deficiency spots) to nonspecific findings (e.g., hemorrhages, detachments). It emphasizes that funduscopy is a noninvasive window to vasculature and nervous tissue, enabling early diagnosis and monitoring of conditions such as hypertension, infections, metabolic disorders, and neoplasia. Clinically, recognizing these ocular manifestations can expedite diagnosis, guide treatment, and improve outcomes in companion animal practice.

Full summary

5,100 CHARS

**Background** The fundus is unique because it allows noninvasive, uninterrupted visualization of vasculature and nervous tissue. Retinal venules and arterioles can reveal changes in color, diameter, outline, and tortuosity, while the retina and optic nerve may show alterations in thickness, inflammatory infiltrates, hemorrhages, or detachments. Some retinal manifestations are pathognomonic for systemic diseases, and fundus examination is an essential part of the comprehensive physical examination in companion animals. This review focuses on naturally occurring systemic illnesses in cats and dogs that manifest in the fundus, using the DAMNIT-V classification (Degenerative/Developmental, Anomalous, Metabolic, Neoplastic, Nutritional, Inflammatory, Toxic, Traumatic, Vascular).

**Methods** The authors conducted a comprehensive literature review of systemic diseases reported to produce retinal or fundic abnormalities in cats and dogs. They describe normal species- and breed-related variations (e.g., tapetal color, optic nerve myelination, retinal vasculature patterns) and then systematically present each disease category with representative clinical findings, diagnostic approaches, and treatment implications. The review is not exhaustive but covers the most clinically relevant conditions.

**Key Results** - **Degenerative**: Progressive retinal atrophy (PRA) is a group of inherited retinal degenerations causing tapetal hyperreflectivity, vascular attenuation, and optic atrophy. Syndromic forms (e.g., Bardet-Biedl syndrome in dogs) may include obesity, renal abnormalities, and sperm defects. Lysosomal storage diseases (e.g., mucopolysaccharidoses, gangliosidoses) are rare but can cause retinal mottling, pigmentary changes, and atrophy. - **Developmental**: Oculoskeletal dysplasia in Labrador Retrievers and Samoyeds (mutations in COL9A2/COL9A3) presents with short-limbed dwarfism, cataracts, retinal dysplasia, and detachment. Heterozygotes show multifocal retinal folds. - **Anomalous**: Retinal dysplasia in cats is often due to perinatal feline panleukopenia or FeLV infection. Merle ocular dysgenesis in dogs (SILV gene mutation) causes chorioretinal colobomas, optic nerve colobomas, and hearing deficits in homozygous animals. - **Metabolic**: Lipemia retinalis (peach-cream discoloration of retinal vessels) is pathognomonic for hyperlipoproteinemia/hypertriglyceridemia. Diabetic retinopathy occurs in ~21% of dogs after phacoemulsification (median onset 1.4 years post-DM diagnosis); 20% of dogs develop signs within 2 years. Hypertensive retinopathy is common: 62% of hypertensive dogs (systolic BP >160 mmHg) have at least one ocular sign. - **Nutritional**: Taurine deficiency in cats causes feline central retinal degeneration (FCRD), a progressive condition starting as ellipsoidal hyperreflectivity in the area centralis. Vitamin E deficiency in dogs produces pathognomonic small light-brown rounded spots (lipofuscin accumulation) and is responsive to supplementation. - **Neoplastic**: Metastatic neoplasms (e.g., lymphoma, mammary carcinoma) cause choroidal involvement, subretinal hemorrhages, and retinal detachment. Angioinvasive pulmonary carcinoma in cats (lung-digit syndrome) presents with wedge-shaped ischemic chorioretinopathy and is pathognomonic. - **Inflammatory**: Optic neuritis (e.g., from meningoencephalitis of unknown origin) presents with loss of optic nerve margins, hemorrhages, and blindness; 69.4% of treated dogs remained blind. Infectious causes include systemic mycoses (blastomycosis, cryptococcosis, histoplasmosis), tick-borne diseases (ehrlichiosis, anaplasmosis, Rocky Mountain spotted fever), viral (FIP, canine distemper), protozoal (toxoplasmosis, leishmaniasis), and parasitic (Cuterebra larval migrans with crisscrossing retinal tracts). - **Toxic**: Enrofloxacin can cause permanent retinal degeneration in cats. Ivermectin toxicity (especially in ABCB1 mutant dogs) may cause blindness with retinal edema and folds. - **Vascular**: Retinal hemorrhages are nonspecific but most commonly due to systemic hypertension. Hyperviscosity (from gammopathies) causes dilation and tortuosity of both arteries and veins, while hypertension primarily affects arteries. Anemic retinopathy in cats (e.g., from haemobartonella) shows pale vessels and hemorrhages.

**Clinical Implications** Funduscopy is a powerful, noninvasive tool for detecting systemic disease in cats and dogs. Pathognomonic findings (e.g., lipemia retinalis, vitamin E deficiency spots, FCRD, lung-digit syndrome lesions) can directly guide diagnosis. Nonspecific findings (e.g., hemorrhages, detachments) warrant thorough workup for hypertension, coagulopathy, infection, or neoplasia. Early recognition improves prognosis (e.g., hypertensive retinopathy can be reversible with prompt treatment). Genetic testing is available for many inherited retinal diseases and can inform breeding decisions. The authors stress that familiarity with normal variations and the ability to distinguish active from static lesions are essential for accurate interpretation.