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Luis Lima Pompeo Marinho, Laurence Mireille Occelli, Nate Pasmanter, Andre Tavares Somma, Fabiano Montiani-Ferreira, Simon M Petersen-Jones; Autosomal recessive night blindness with progressive photoreceptor degeneration in a dog model. Invest. Ophthalmol. Vis. Sci. 2019;60(9):465.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the early stages of progression of an unusual autosomal recessive inherited retinal degeneration in dogs (Somma et al 2017. Vet Ophtho 20:450).
Three littermates from a breeding between two dogs with this condition were monitored from birth to 12 months of age by ophthalmoscopic examination, electroretinography (ERG), functional vision testing (VT) and spectral domain optical coherence tomography (SD-OCT).
Scotopic and photopic ERGs from the earliest age examined lacked a b-wave. Initially a-waves of normal amplitudes were present, although they appeared to be slightly delayed. Their amplitudes progressively decreased and threshold of response became elevated over the first year of life. The loss of photopic responses was faster than that of scotopic. Modeling of the a-wave showed that by 9 months of age the Rmax had deteriorated to ~10% of that present at 8 weeks. SD-OCT imaging revealed a progressive thinning of the receptor plus (photoreceptor layer). Furthermore, there was a progressive loss of definition of the layers representing the photoreceptor inner and outer segments. Two of the 3 dogs also developed small focal retinal bullae (detachments) in both eyes starting from as early as 3 months. These disappeared with disease progression. Vision testing showed that in bright conditions dogs were able to exit the vision testing device accurately and rapidly. At lower lighting levels they frequently failed to identify the open exit and took much longer to exit the device. Wild-type dogs choose exits correctly almost 100% of the time at all light levels used and exit rapidly. There was no obvious deterioration in vision testing results over the study period.
The lack of an ERG b-wave indicates either a lack of transmission of the light induced signal to ON bipolar cells, or a lack of function of ON bipolar cells. Such ERG changes are seen in humans with conditions including complete congenital stationary night blindness and congenital cone-rod synaptic disorder. However, unlike human patients with these conditions where progression is rarely reported the dogs in this study had a relatively rapid loss of rod and cone photoreceptor function accompanying a thinning of the outer retina. This represents a new canine model of a congenital night blindness associated with progressive photoreceptor degeneration.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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