As I understand Genjutsu is, affecting the opponent's chakra network with your own chakra through some medium, and create illusions in their mind. It's basically 'Yin Release' through some medium. Incase of Sharingan users, it's done through eyesight. They can cast Genjutsu when the opponent see the caster's Sharingan. That way they imply their chakra into the opponent's body.
Incase of Sage Toads and Tayuya, It's through sound. So, whoever is within the range could be affected by the Genjutsu.
The question is, Is there any other way to cast Genjutsu ? How come Kurunei is able to cast Genjutsu? Is it through eyes?