Editing Eyes of the Emperor (section)

=Gene-seed=
The Occulobe of the Eyes of the Emperor is one of the most potent among all of the Legiones Astartes, but it has a high risk of rejection. More of their Neophytes suffer from a problem with this organ's implantation than any other. These unfortunates suffer from "The Mark of the Vardhana" - permanent blindness and strange hallucinations which render them unfit even for use as Serfs. It is a closely-kept secret among the Apothecaries of the Legion that Neophytes struck down with the Mark are used for cultivating gene-seed before being euthanised.

Some speculate that the terrible effects of the Mark are a consequence of the psychically-energising effects of the Vardhana's gene-seed.  Certainly, the Primarch himself was an extraordinarily potent psyker and Master Silence's prowess is well-known.  However, if the Legion's Librarus as a whole was skilled and loyal, it was not overly large and there were no reported cases of an aspirant without psychic potential becoming a psyker as a result of the gene-seed.