Scanning electron micrographs of photoreceptor outer segments taken from animals at 3, 6, 12 and 24 months of age.

<p>In each case the right hand panel is a higher magnification of that on the left and the orientation is such that the RPE would be to the top and the outer nuclear layer to the bottom. Even at 3 months of age deposits can be found on outer segments, however they are more common towards the tip of the outer segment than the base. They are largely spherical in morphology or have rounded edges. By 6 months, their coating has increased and the deposits are present along the length of the outer segment. At 12 months the deposits have thickened, but also appear to have changed qualitatively (See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013127#pone-0013127-g007" target="_blank">Figure 7</a>). At 24 months while thick deposits remain the tips of many outer segments have enlarged and those that remain are shorter making direct comparison with earlier stages difficult.