In addition to the complete absence of outer segments, Crx-/- retinas exhibited three other notable pathologies in the outer segment layer. First, an abnormal deposition of matrix of unknown identity was noted (Figure 3A, mx). Second, sporadically displaced nuclei were found residing in the space abutting the PE. Occasionally, these nuclei appeared pyknotic (Figure 3A, n); but, more frequently exhibited the heterochromatin pattern typical of photoreceptors (data not shown), strongly suggesting that they belonged to ectopic photoreceptors. The third pathological entity noted in the outer segment layer were numerous small vesicles (Figure 3A arrow) 100 to 200 nm in diameter. They appeared to be emerging from the inner segments, as scanning electron microscopic images showed spherical structures budding from the inner segments (Figure 3C, arrow).