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E.-O. Ropstad, K. Narfsröm, E. Bjerkås, R. Bragadottir; Retinal pigment migration in the Standard Wire Haired Dachshund with early onset cone-rod dystrophy caused by a mutation in the NPHP4 gene. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4505.
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To describe morphologic retinal changes in Standard Wire Haired Dachshunds (SWHD) affected by early onset cone-rod dystrophy (crd) caused by a mutation in the NPHP4 gene.
5 dogs homozygous for the NPHP4 mutation were subjected to fundoscopic imaging and Optical Coherence Tomography (OCT) examination at ages 3, 20(2), 33 and 56 months. All dogs were sedated during the entire OCT procedure by the use of medetomidine hydrochloride (0.033 mg/kg IM; Domitor vet® 1mg/ml, Orion Corp, Turku, Finland). Tropicamide (Mimins Tropicamide 0.5%, Chauvin Pharmaceuticals Ltd, Surrey, UK) was installed bilaterally at least 20 minutes prior to OCT examination in order to achieve pupil dilation. A macula scanning program (Stratus OCT, Carl Zeiss Meditec Inc, Germany) was used, resulting in 6 sectional images from each eye. Unaffected age matched dogs of same breed were used as controls. Retinal specimen from 2 crd-affected dogs, aged 3 and 20 months, sacrificed in close proximity with the OCT examination, were evaluated by use of light- and electron microscopy. Retinas from age matched unaffected dogs served as controls.
OCT images from crd-affected dogs aged 20 months and up showed intra-retinal hyper-reflectivity in the non-tapetal part of the retina, consistent with pigment migration, findings that corresponded to fundoscopic images. Pigment migration into the subretinal space was evident upon light- and electron microscopic examination of specimens from the 20 months old dog. No evidence of pigment migration was evident upon OCT examination of the youngest crd affected dog, in correspondence with morphological and fundoscopic findings. None of the control dogs showed evidence of pigment migration upon OCT, morphologic and fundoscopic examination.
OCT is a valuable diagnostic method for documenting retinal pigment migration in vivo. Early onset crd in SWHD is characterized by a marked pigment migration in the inferior (non-tapetal) fundus already at early stage of disease, a finding not previously documented in canine models for early onset retinal dystrophies.
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