Hereditary Tapetal Abnormality in the Beagle

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Abstract
Beagles having no ophthalmoscopically visible tapetum and a uniform reddish-brown fundus reflex are occasionally encountered. Two Beagles with this ocular variant were acquired in order to assess its reproducibility and its usefulness in fundus fluorescein angiography. A mating of these Beagles resulted in a litter of 7 female and 2 male puppies, none of which showed any ophthalmoscopic evidence of a tapetum when examined at 7, 12, and 26 weeks of age. Fluorescein angiography, performed on two puppies when approximately 13 weeks of age, produced angiograms superior in quality to those obtained from normal dogs. However, retinal capillary definition was less than the optimal obtained in nontapetal primates. Light microscopy revealed a normal layering of tapetal cells between the retinal pigment epithelium/choriocapillaris and the choroid. Electron microscopy revealed irregularly spaced and abnormal intracellular inclusions instead of the normal regularly spaced tapetal rodlets. There was present in these eyes sparse pigmentation of the pigment epithelium of the ciliary body, iris, and peripheral retina.

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