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Bjorn Ekesten, Suvi Mäkeläinen, Ulrika Kjellstrom, Tomas F Bergström; Fundus autofluorescence and foveal appearance in Labrador Retriever dogs with an ABCA4 loss-of-function mutation.. Invest. Ophthalmol. Vis. Sci. 2020;61(7):665.
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We have recently reported on an ABCA4 loss-of-function mutation in Labrador Retrievers (LRs) causing a slowly progressive retinal degeneration and visual impairment (Mäkeläinen & al. PLoS Genetics, 2019). Here we study fundus autofluorescence (FAF) and foveal morphology in LRs heterozygous or homozygous (STGD) for this mutation.
FAF- and infrared (IR) cSLO images and foveal OCTs were obtained from 6 LRs (11 to 128 months old) homozygous for the mutation, 5 heterozygotes (11-149 months old) and 7 wildtypes (13-141 months old) using a Heidelberg Spectralis HRT + OCT. Pupils were dilated using tropicamide and corneas were kept moist with artificial tears. LRs were lightly sedated with medetomidine and butorphanol during imaging.
On IR cSLO, the fovea was outlined by a hypo- and sometimes hyperreflective ring in the youngest STGD LRs, whereas the hyporeflectivity extended into the surrounding area centralis and along the visual streak in middle-age dogs. Eventually, the entire tapetal fundus appeared mottled in old STGD LRs. The fundus of young carriers appeared normal, but in middle-aged and older carriers, the appearance of the foveal area was similar to the youngest STGD LRs.Decreased FAF was restricted to the foveal area in young STGD LRs, but spread along the visual streak in older affected dogs. The fovea was surrounded by a more hyperreflective ring. In old STGD LRs, increased FAF could also be seen in the non-tapetal area. Young and middle-aged carriers appeared normal, whereas increased foveal FAF was seen in an old carrier.OCT showed significant thinning of the outer nuclear layer (ONL) in STGD LRs compared to wildtype, whereas foveal and parafoveal ONL thickness in carriers ended up inbetween affected and wildtype. Foveal ONL thinning was evident already in the youngest STGD LRs. The ONL, both foveal and parafoveal, was even more reduced in older STGD LRs.
cSLO and FAF indicate that the ABCA4 loss-of-function mutation leads to damage and loss of retinal pigment epithelial cells/RPE in LRs already before 1 year of age. The abnormal appearance spreads from the cone-rich areas to more peripheral parts of the retina. Older carriers may show a mild phenotype. OCT shows reduction of foveal photoreceptor nuclei already in young STGD LRs, which progresses and spreads with increasing age. Hence, the foveal area seems to be affected first in STGD LRs.
This is a 2020 ARVO Annual Meeting abstract.
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