Noninvasive imaging of the tree shrew eye: Wavefront analysis and retinal imaging with correlative histology

• Published in: Experimental eye research 2019-08, Vol.185, p.107683-107683, Article 107683
• Main Authors: Sajdak, Benjamin S., Salmon, Alexander E., Cava, Jenna A., Allen, Kenneth P., Freling, Susan, Ramamirtham, Ramkumar, Norton, Thomas T., Roorda, Austin, Carroll, Joseph
• Format: Article
• Language: English
• Subjects: Aberrometry; Adaptive optics; Animals; Cell Count; Cone photoreceptors; Corneal Wavefront Aberration - physiopathology; Megamitochondria; Microscopy, Electron, Transmission; Ophthalmoscopy; Optical coherence tomography; Optical Imaging; Refraction, Ocular - physiology; Refractive Errors - physiopathology; Retina - diagnostic imaging; Retina - physiopathology; Retinal Cone Photoreceptor Cells - cytology; Retinal Cone Photoreceptor Cells - physiology; Tomography, Optical Coherence - methods; Tree shrew; Tupaia
• ISSN: 0014-4835; 1096-0007; 1096-0007
• DOI: 10.1016/j.exer.2019.05.023

Tree shrews are small mammals with excellent vision and are closely related to primates. They have been used extensively as a model for studying refractive development, myopia, and central visual processing and are becoming an important model for vision research. Their cone dominant retina (∼95% cones) provides a potential avenue to create new damage/disease models of human macular pathology and to monitor progression or treatment response. To continue the development of the tree shrew as an animal model, we provide here the first measurements of higher order aberrations along with adaptive optics scanning light ophthalmoscopy (AOSLO) images of the photoreceptor mosaic in the tree shrew retina. To compare intra-animal in vivo and ex vivo cone density measurements, the AOSLO images were matched to whole-mount immunofluorescence microscopy. Analysis of the tree shrew wavefront indicated that the optics are well-matched to the sampling of the cone mosaic and is consistent with the suggestion that juvenile tree shrews are nearly emmetropic (slightly hyperopic). Compared with in vivo measurements, consistently higher cone density was measured ex vivo, likely due to tissue shrinkage during histological processing. Tree shrews also possess massive mitochondria (“megamitochondria”) in their cone inner segments, providing a natural model to assess how mitochondrial size affects in vivo retinal imagery. Intra-animal in vivo and ex vivo axial distance measurements were made in the outer retina with optical coherence tomography (OCT) and transmission electron microscopy (TEM), respectively, to determine the origin of sub-cellular cone reflectivity seen on OCT. These results demonstrate that these megamitochondria create an additional hyper-reflective outer retinal reflective band in OCT images. The ability to use noninvasive retinal imaging in tree shrews supports development of this species as a model of cone disorders. •Highlights: Noninvasive imaging of the tree shrew eye: wavefront analysis and retinal imaging with correlative histology.•Tree shrew optics are well-matched to their cone mosaic topgraphy•Tree shrews are highly amenable to high-resolution retinal imaging in vivo.•Retinas shrink by ∼4–5% during fixation, affecting cone density measurements.•Megamitochondria affect the appearance of optical coherence tomography images.