Abstract
This case report investigated the cause of visual impairment at night in Beagle dogs in a family of 12 individuals. Four related adult male Beagles with impaired night vision and eight related Beagles (three females, five males) underwent a complete ophthalmological examination at the ophthalmology service. Electroretinography was performed on four dogs with impaired night vision after dark adaptation to evaluate retinal function. Retinoscopy was performed in 12 dogs in a standing or sitting position to assess refraction. Axial globe measurements were conducted using B-scan ultrasonography in nine dogs. In total, twelve adult Beagles (nine males, three females) from four generations were evaluated, with nine dogs showing impaired night vision. Ophthalmic examinations revealed no abnormalities that could explain the visual impairment. Electroretinography showed normal retinal function. In total, 83.3% (10/12) of the dogs were myopic, with refractive errors ranging from -1.25 to -6.25 diopters (D). All dogs with night vision impairment were significantly more myopic (median: -4.88 D) than those without impairment (median: -1.25 D). In two myopic dogs, the insertion of contact lenses improved navigation in the dark maze test. Myopic dogs showed a significantly greater vitreous body depth (10.1 mm; range 9.7-10.3 mm) compared to emmetropic dogs (9.5 mm; range: 9.4-9.6 mm). These findings suggest that in dogs with night vision impairment, retinoscopy should be included in the ophthalmological exam to exclude myopia as a potential cause. Further research is needed to determine the cause of myopia in the tested Beagles and to investigate possible genetic factors.