Useful Vision in Mice Lacking Photoreceptor Outer-Segments

Abstract

Purpose: : To establish the residual function of Rds deficient photoreceptors and the visual pathogenesis of the Rd2 allele. Mice homozygous for the Rd2 disease causing allele of the Rds gene (Rds-/-) do not develop photoreceptor outer segments and undergo protracted photoreceptor degeneration. Mice heterozygous for this partially dominant allele (Rds-/+) also have morphological disruption of the photoreceptor outer segments. However, the function of the photoreceptors and the state of vision in these mice has not been characterized.

Methods: : Visual capacity was defined by visually guided behavior, electroretinography and retinal morphology in Rds-/-, Rds-/+, and wildtype mice at specified ages.

Results: : Our results show that under elevated illumination 3 month old Rds-/- mice have vision sufficient to guide movement but this is severely reduced at 12 months. At 2-months a weak ERG is recordable only at higher illumination and declines further with age.

Conclusions: : These preliminary results suggest that rod outer-segments are not essential to the rods ability to signal light capture events. The photoreceptors of Rds-/- mice have residual photopigment in the cell body. Therefore the observation of useful vision in young Rds-/- mice suggests elevated illumination can increase the number of light capture events sufficiently for vision, at least early in degeneration. This also shows that residual photoreceptor function enables refinement of visual pathways and suggests the validity of a function restoring or degeneration halting treatment.

Keywords: photoreceptors: visual performance • degenerations/dystrophies • electroretinography: non-clinical