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E.–O. Ropstad, K. Narfstrom, E. Bjerkaas; Clinical Characterization of Early Onset Cone–Rod Dystrophy in the Wire Haired Dachshund . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5790.
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To characterize the clinical changes in early onset cone–rod dystrophy (crd) in a strain of Wire Haired Dachshunds (WHDs) and evaluate whether these changes can be used for diagnosis.
A colony of WHDs segregating for crd has been established by back crossing the founder with his daughters. A total of 75 dogs were included in the present study. The diagnosis of crd was based on bilateral full field ERG (ETi–020i, Scanditronics Medical AB, Uppsala, Sweden) findings using a standardized protocol for evaluation of rod and cone function. Unrelated age matched WHDs were used as controls. The dogs were tested in an indoor maze under scotopic and photopic conditions. The pupillary light reflexes (PLRs) were evaluated subjectively by using a focal light source ( Heine 6–21–301, Germany). The dogs (5–304 weeks) were divided into 3 age groups and PLRs recorded as normal, delayed, pulsating, pin–point or dilated/incomplete. Fundoscopic and biomicroscopic examinations were also performed.
Evaluation of PLRs showed that in affected dogs the majority were abnormal with pin–point sized pupils in the youngest age group. Older affected dogs displayed delayed or dilated/incomplete PLRs. It was not possible to differentiate affected dogs from normal controls using the maze test. ERG recordings showed that the cone system was more affected than the rod system. Significant differences in photopic a–wave and flicker amplitudes between control and affected dogs were found already in the youngest age group.
Early abnormalities in PLRs are a valuable diagnostic parameter. However, maze testing is not a good method for detecting early signs of crd in WHDs. ERG was found to be the most consistent and reliable clinical diagnostic tool. Further research includes morphologic and molecular genetic investigations. None
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