Like all other ruminants, the pupil is oval shaped with the horizontal axis being the longer one. The difference comes with structures called 'iridic granules' or 'corpora nigra'. These are dark lumpy masses coming off the iris at the top and/or bottom of the pupil margins. They are thought to shade the eye from bright sunlight.
Horses only have these on the top pupillary margin and they are more rounded. Cattle and sheep have more rounded iridic granules like horses, but on both sides (top and bottom) of the pupil.
Llamas have iridic granules on the top and bottom of the pupil as well, however, they are more elongated than rounded. In bright sunlight these iridic granules can actually interdigitate to completely cover the centre of the pupil. This leaves just two holes open on either end of the pupil.
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