Unexpected Retinal Abnormalities in the Cone-Dominant Northern Tree Shrew

The cone-dominant northern tree shrew has been used in a wide range of vision research studies. Given the similarity of their visual system to primates, there have been extensive in vivo and ex vivo studies of the visual system from retina to cortex. Tree shrews have long been used to study myopia and more recently, experimental models of glaucoma and diabetic retinopathy have become available. They are also amenable to various noninvasive imaging methods-previous studies have established their retinal structure and function through scanning laser ophthalmoscopy, optical coherence tomography, and adaptive optics scanning light ophthalmoscopy. In this study, we characterized abnormal retinal findings in a cohort of presumed normal tree shrews via noninvasive imaging. In 31 tree shrews, 15 were found to have one of three distinct retinal phenotypes. The first (n = 10) is the presence of hypo-reflective and hypo-autofluorescent foci nasal to the optic nerve across the horizontal meridian. The second phenotype (n = 4) is a mottled fundus appearance with disrupted outer retinal laminations in a region temporal to the optic nerve. The last observed phenotype (n = 1) appeared as widespread patches of decreased near-infrared reflectance and short-wavelength autofluorescence intensity which aligned with regions observed to have inner retinal layer thinning and disrupted cone mosaic. With the growing use of the tree shrew as an animal model in vision research, it is essential to determine the etiology of the observed abnormalities, through future genetic testing, blood chemistry panels, histology, and/or longitudinal imaging.