Tapetal dysplasia in a Swedish Vallhund dog

Objective: To describe the gross, histopathological, and ultrastructural findings in a dog with bilateral tapetal dysplasia.

Procedures: The globes of a 15-year-old neutered male Swedish Vallhund dog with a ventrally displaced tapetum in both eyes were fixed in 10% formalin and submitted to the Comparative Ocular Pathology Laboratory of Wisconsin for histological evaluation. Sections were stained with hematoxylin and eosin, Masson's trichrome, and Melan-A immunohistochemistry (IHC), and tissues were subsequently processed for transmission electron microscopy.

Results: Bilateral fundic and gross examination revealed a tapetal fundus inferior to the optic nerve head (ONH) and a nontapetal fundus with mild scattering of tapetal tissue superior to the ONH. Histologically, there was decreased pigmentation of the retinal pigment epithelium with only a few melanin granules in the peripheral retina. The affected tapetum was relatively acellular and fibrous with occasional tapetal cells scattered throughout the inner choroid or displaced into the vascular outer choroid. Special stains revealed that the tapetum was mostly composed of collagen (Masson's trichrome) and failed to express Melan-A (IHC) unlike a normal canine control tapetum. Ultrastructurally, the tapetum was markedly dysplastic both superior and inferior to the ONH with no uniformly arranged tapetal cells. The few cells identified within the tapetum contained irregularly arranged and disorganized electron-dense structures within their cytoplasm, which were interpreted as dysplastic tapetal rodlets.

Conclusions: Based on microscopic and ultrastructural findings, this is the first report of tapetal dysplasia in a dog.