In sanskrit & kannada, 'Eesha' / '
Isha' means 'Lord' oftenly refered to lord 'Eeshwara'.
Gramatical usage:-
Gana + Eesha /
Isha=
Ganesha Maha + Eesha/
Isha =
Mahesha Ravi + Eesha /
Isha= Ravisha / Raveesha < Lord of Sun>
Venkata + Eesha/
Isha = Venkatesha
Rama + Eesha/
Isha =
Ramesha < Lord /husband of Godess
Sita >
Uma+
Esha/
Isha = Umesha < Lord
Shiva / Husband of Uma/Parvathi>
etc. This modification of name is an example of 'Guna sandhi' 'a' kaara + 'i' kaara = e' kaar .
But, in English as it is very flexible we will tend to use 'E' , ''EE' and 'I' interchangeably according to regional pronunciation and practice.