There is a black structure called the granula iridica or pupillary ruff that extends into the pupillary opening in the iris of the alpaca. It has upper and lower sharply fringed portions which interdigitate in bright sunlight and eliminate the pupillary opening. The upper portion is more prominent than the lower portion. This structure probably serves a protective function for the deeper structures of the eye against UV light damage, especially at high altitude in the native countries of alpacas in South America. The pupillary opening is horizontally oriented and is roughly oval in shape
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