What is "Ishon"?
Rashi: It is the black of the eye; sight depends on it. It is called Ishon due to the blackness; it is an expression of darkness. Hashem made a guard for it, the eyelid, which constantly covers it. Radak - it is called Ishon because the form of an Ish (man) is seen in it. The [suffix] Vov Nun diminishes, because the image [of the man] is small. Also Vov Nun in Shabbaton, which refers to added Kedushah 1 . Also Vov Nun of "ha'Aminun" diminishes (Amnon's important).
He said that Vov Nun diminishes! Perhaps it is added Kedushah, but it is less Kadosh than Shabbos itself. (PF)
Why does it say "Ishon" and "Bas"?
Radak: Ishon is Samuch to Bas. Bas is a noun - the eyeball, from which is sight. Ishon is an adjective.
