Hereditary visual impairment in a new mutant strain of chicken, GSN/1

Visual pathways of a new mutant of chicken (GSN/1) with hereditary visual impairment were ophthalmologically, electrophysiologically, and histopathologically examined. Clinically, GSN/1 chickens drooped and had decreased locomotor activity. As an indicator of visual acuity, the spatial frequency characteristics of GSN/1 chickens showed poor scores at high frequency. No abnormal findings were observed ophthalmoscopically in the fundus of them. The amplitudes of a and b waves of the electroretinogram in GSN/1 chickens revealed no abnormal findings for xenon flash stimuli with different intensities. However, responses of the visual evoked potential in GSN/1 chickens were insensitive to xenon flash stimuli. Histologically, the retina of GSN/1 chickens was slightly hypoplastic and the retinal ganglion cells decreased in number, although there were no degenerative or reactive changes. The optic tectum, especially the stratum opticum and the stratum griseum et fibrosum superficiale were hypoplastic and contained reduced numbers of optic nerve fibers. The sublayers of the stratum griseum et fibrosum superficiale were disorganized, in which axons of the optic nerve were distributed irregularly. These findings suggest that visual impairment observed in the new mutant GSN/1 chicken may be related to developmental defects in the visual pathways, especially in the optic tectum.