• Background Sensitivity: mice no longer display the spotting phenotype when backcrossed from a CAST/EiJ background onto a C57BL/6 background (J:85459)

• Background Sensitivity: 19% of mice do not display the spotting phenotype on a CAST/EiJ mixed background

• retinal pigment epithelium vacuolation

• nonimflammatory retinal degeneration is observed in the inner and outer nuclear layers, the outer plexiform layer and photoreceptor outer segments

• appearance of retinal lesions or spots is variable

• fundus lesions(spots) coalesce to form diffuse lesions or large patches and are visible by histological examination as early as 6 weeks of age

• retinal pigment epithelium vacuolation

• mice exhibit large, irregularly shaped spots concentrated in the inferior nasal quadrant of the fundus as early as week 3 that correspond to retinal folds and pseudorosettes

• retinal thinning in both the inner and outer segment is observed

• Muller cells exhibit increased electron density and cytoplasmic strands that are more easily traced through the plexiform layer than in wild-type mice

• the photoreceptor lamellae breaks down

• in the region of focal degeneration photoreceptors are lost

• the photoreceptor inner segments lose their orderly arrangement

• by 5 months the inner segment approaches the retinal pigment epithelium

• swelling occurs in portions of the inner segments

• at 4 weeks the photoreceptor inner segments are 25% shorter

• by week 10 the outer segment begins to fragment

• by 5 months only a few outer segment fragments remain

• the photoreceptor outer segments are shortened

• the external limiting membrane in the retina is fragmented and disorganized at 2 weeks and is more severe at 4 weeks

• in older mice, the retinal outer nuclear layer is reduced to a single row of nuclei

• Muller cells exhibit increased electron density and cytoplasmic strands that are more easily traced through the plexiform layer than in wild-type mice

• the photoreceptor lamellae breaks down

• in the region of focal degeneration photoreceptors are lost

• the photoreceptor inner segments lose their orderly arrangement

• by 5 months the inner segment approaches the retinal pigment epithelium

• swelling occurs in portions of the inner segments

• at 4 weeks the photoreceptor inner segments are 25% shorter

• by week 10 the outer segment begins to fragment

• by 5 months only a few outer segment fragments remain

• the photoreceptor outer segments are shortened